Thursday, December 11, 2008
We started out with the pack and just tried to cruise the initial downhill and subsequent climb, which became steeper eventually. David kept telling me I was pushing too hard, and he was right of course—with a heart rate in the mid 160s, I couldn’t sustain that pace the whole way, but I was going to do my best to meet the first cutoff at Bear Gulch (18.9 km, 2:50). We did fine, running up the hills, and slowing to a walk when necessary, and made it to the first aid station (King’s Mtn) about ten minutes faster than I had estimated. I had added an antioxidant tablet (vitamins A, C, and E) and Nuun (for electrolytes) to my water bottle on the way up. (Apparently all the oxidative stress from running generates free radicals that deplete plasma peroxide neutralizing capacity—See for example, the review “Vitamin C for preventing and treating the common cold,” a review of 29 trials involving some 11,000 participants which, while finding minimal effects in general populations, found significant benefit of Vitamin C supplementation in “persons exposed to brief periods of severe physical exercise and/or cold environments.” See also, “Antioxidant supplementation prevents exercise-induced lipid peroxidation, but not inflammation, in ultramarathon runners.”) I added Conquest to the mix at the aid station and guzzled some Coke (for the caffeine and sugar), and tried to choke down a couple of Cliff blocks. There followed the undulating Skyline Trail, deceptively difficult and seemingly unending, before reaching Bear Gulch aid station in 2:30 (well ahead of the cutoff time—I was so thrilled, since our training runs were not so successful). I used one Gu before this aid station, though it’s unclear whether it did any good. By this time, the speedy 35K runners who started 30 minutes after we did had started to pass us—showing us how it is supposed to be done.
The descent into Wunderlich was an enjoyable respite, even though the trail is rough in places and my quads were starting to complain after we’d descended about 1000 feet. We met the front runners heading back up, smiling and making it look easy, and I just tried to keep it steady and not trip or sprain an ankle or something. I trudged back up the hill munching on my sandwich as best I could (it’s hard to eat solid food when there is no saliva!) and washing it down with my antioxidant/electrolyte supplemented sports drink. I conserved energy and fought off an urge to pull over and sleep, and put in some halfhearted jogging at David’s urging. We made it back to the Bear Gulch aid station (33k) by 4:30, and plunged back onto the Skyline Trail for the return trip. The next descent on the Chinquapin trail was heavenly, but they routed us back up the Dean trail (another slow-to-a-walk stretch) before flying down the road to the finish.
I tried to keep up the pace throughout the race, but after a few hours, my body seemed willing to function only at its solid aerobic level (AKA slow). For example, in the descent into Wunderlich, I averaged something like a 9 min mile pace at a HR of 145–150; while during the descent in Huddart I averaged a HR of 140 at the same pace, at least as far as I can tell from my Garmin data, in contrast to the initial part of the race.
What about nutrition during this race? We started out with a Vespa sample that Peter Defty gave us at the Zombie Runner store opening. I supplemented somewhat with carbs (2 Gu’s total, half a ham sandwich, handful of potato chips, few small cups of Coke, sports drink with sugar). I figure since I was pushing into the glycolytic realm (judging by my generally heavy breathing and high heart rate—at least initially, later on I was too tired for that nonsense and HR stayed mostly below 150), I may well be limited by glycogen depletion and some carb supplementation could help. I don’t know that it does, but I did it anyway. David did the entire race on essentially no carbohydrate, using his home-brew protein shake, this time based on coconut milk instead of cow’s milk; he has become a firm believer in running on fat as fuel. Certainly his energy level was more constant than mine (I really wanted a nap on the way back up Wunderlich), but it’s not clear whether that was because I was pushing my limits harder than he was, or his nutrition was superior. I do know that some food is necessary—I’ve experienced nausea with no food (which could, however, be controlled with just a little chicken broth), but I’m not convinced that Gu’s and sugar are really all that helpful.
So what changed? How did our times get better? Since we’ve been doing ultra runs, the weight loss has stalled. I think that some fat loss is still occurring, and there is increased muscle and blood volume and sometimes even swelling and water retention that accounts for some of the stall. But as there has been no further weight loss, that cannot be the reason for improvement. Since the Firetrails 50 miler and SF One Day, we decided it was time to focus on some basic running skills, and actually “train” on occasion. Having run track as a sprinter in my youth, I knew enough to design some simple intervals to see what various paces feel like. It was a pleasant reminder to feel what a 7- or 8-minute pace is like again, and strangely addictive (I want to keep doing it, even though I can’t keep it up for long, unfortunately). We’ve started timing our runs so we can see what might be working, and are including some fartlek segments and some hill sprints in addition to occasional track workouts. I think the most important improvement has come from running on roads, since trail runs inevitably make me stop to walk, if only to admire a beautiful view, or for hills, while road running provides fewer interruptions, allowing you to work on cadence and breathing and consistency, what I’ve been sadly lacking.
So we’ll keep it up and see where it goes!
Friday, November 7, 2008
So why so slow? I’m 52 years old, and seem to have lost much of whatever speed I ever had (a middle of the pack sprinter in high school and college). I was on track for a 3:20 marathon before a calf injury slowed me down—PR of 3:27), now 25 years ago. Just how slow must I be now? Is it possible for a person to regain the health and vigor they had when they were younger? This is the grand experiment, and may fail badly, but that’s the question. Can I get back what I once had? Can I get better? Do I have to be resigned to being old and slow? Can I improve my health while I do it?
So it seems it’s time for some more serious training. We’ve started doing small interval workouts on the track (a few 200s, 400s and 800s) and some tempo runs, just to try to jog the memory of those quiescent fast twitch muscles (no pun intended). I was dismayed to realize that I’ve lost all sprint speed, and running up on my toes feels like I’m going to spazz out and fall on my face. Just doing 400s at an 8-minute-mile pace seems fast at this point. I’m hoping that will change, but how to improve?
Recently, I came across a link to a blog I haven’t discovered before, with an interview with Dr. Maffetone about training for endurance events that was quite interesting. He’s the inventor of the 180 rule (basically subtract your age from 180 to calculate your maximum aerobic heart rate [HR]). According to this method, you train at a level that achieves the desired HR, and you naturally speed up even though you maintain this level of effort, as you train your body to use fat as fuel. In the interview, he describes how he discovered this method basically by measuring respiratory quotients to determine at what HR fat burning occurred as opposed to carbohydrate burning. According to Dr. Maffetone, anaerobic training can be implemented after base aerobic training, in interval workouts or races, then followed by more base training.
I was intrigued and read some of the other advice on his website (sign up for a free membership). His nutrition advice really surprised me as well—another low carber of sorts! He advocates cutting out all refined carbohydrates, much the same advice of the cardiologist Dr. William Davis who is working hard with his patients to prevent and reverse their atherosclerotic disease.
It’s possible that we’ve already achieved a good grounding in aerobic (fat burning) ability, and that now would be a good time to work on speed. Maybe a good test would be to run a regular road marathon to at least get a good baseline number on my starting point. We’ll have to see how it goes…
Sunday, November 2, 2008
absolutely need plenty of carbohydrates before, during, and after the activity to achieve peak performance, to avoid “crashing” or “bonking,” and to recover quickly. Aid stations are typically stocked almost exclusively with carbohydrates, especially sugars (jelly beans, cookies, M&Ms) and simple starches (potatoes, potato chips, pretzels, gels), with the addition of some limited fats and protein only in the longest events. I’d come to increasingly suspect that this advice is probably wrong, and especially wrong for anyone who has adopted a low-carbohydrate diet and made the physiological adaptation to fat-burning to fuel exercise. I can now add my own anecdotal experience.
I have been restricting my average carbohydrate intake to an estimated 20% or so of calories for about 10 months now. At the same time I have been increasing my exercise level and capability substantially, to the point where I have now completed several 50K running events and one 50-mile event. At first, running seemed harder without the usual high level of carbohydrate intake, but over a few weeks it got steadily easier until fairly suddenly it was much easier. I was able to run uphill again (which I hadn't been able to do for a while); I found my routine breathing rate during comfortable sustained running had slowed by at least a third; I could easily go longer without any food intake besides water.
Nevertheless, for my first 50K event, I consumed more like a 50% carbohydrate meal the night before, and consumed the usual assortment of provided aid station food, avoiding only the simple sugars. The running went well enough, though my weight jumped a few pounds the next day and took three or four days to return to “normal.”
Since then I have been steadily cutting back on carbohydrate supplementation during the run. I did the 50-miler on mostly protein and fat with only a modest amount of carbs thrown in. Then I tried a strict low-carb 50K run, using only a “protein shake” (my own brew of whey protein, soy protein, milk, cocoa, almond meal, and walnut oil) for the entire distance. It worked great! I had steady energy throughout the event (no ups and downs) and was still feeling strong at the end to the point where I did not participate in the post-event food and was happily running around on the beach where the event ended. (The day-after weight gain still occurred; apparently that's not a carbohydrate effect.) So my conclusion is that all this carbohydrate is not needed for successful endurance!
There’s still a question of peak performance. Do you need the carbs and the associated blood glucose spike to do your absolute best? Can you go faster with carbs than without? Does it matter if you’re planning short events (sprints, strength events, etc.) rather than longer endurance events? I don’t know, but I’m increasingly favoring the hypothesis that you don’t actually need much carbohydrate at all once your body is adapted to using fat as its primary fuel.
There are at least a handful of papers related to this topic. These papers all support the idea that only limited amounts of carbohydrates are necessary or even desirable for endurance athletes. See, for example:
Larson-Meyer et al., “Effect of dietary fat on serum and intramyocellular lipids and running performance,” Med Sci Sports Exerc. 2008 May;40(5):892–902 reports 3-day crossover trials of endurance trained runners with low fat (10% fat LFAT) or medium fat (35% fat MFAT), and concludes that “despite approximately 30% lower IMCL [intramyocellular lipids] 0.220±0.032% LFAT, 0.316±0.049% MFAT; P = 0.045) and approximately 22% higher muscle glycogen stores at the start of performance testing (P = 0.10), 10-km performance time was not significantly different following the two diet treatments.” Lipid profiles suggestive of cardiovascular disease were associated with the high-carbohydrate-low-fat diet, and the authors concluded that “even short-term consumption of a low-fat diet may unfavorably alter serum lipids, even in healthy, endurance-trained runners.” (Note that this study did not allow time for adaptation to the different diets, so glycogen and lipid levels in the muscle cells are due only to the acute diets tested);
Vogt et al., “Effects of dietary fat on muscle substrates, metabolism, and performance in athletes,” Med Sci Sports Exerc. 2003 Jun;35(6):952–60, which studied the effect on trained athetes of a high-fat (53% fat) or high-carbohydrate diets (17% fat) for 5 weeks in a randomized crossover design, found that maximal power and vO2-max during an incremental exercise test to exhaustion were not different between the two diet periods, total work output during a 20-min all-out time trial (298±6 vs 297±7 W) on a bicycle ergometer as well as half-marathon running time (80 min 12 s ± 86 s vs 80 min 24 s ± 82 s) were not different between HF and LF. Blood lactate concentrations and respiratory exchange ratios (RER) were significantly lower after HF than after LF at rest and during all submaximal exercise loads. The authors concluded that “muscle glycogen stores were maintained after a 5-wk high-fat diet period whereas IMCL content was more than doubled. Endurance performance capacity was maintained at moderate to high-exercise intensities with a significantly larger contribution of lipids to total energy turnover”;
Lambert et al., “High-fat diet versus habitual diet prior to carbohydrate loading: effects of exercise metabolism and cycling performance,” Int J Sport Nutr Exerc Metab. 2001 Jun;11(2):209–25. No changes were observed in circulating glucose, lactate, free fatty acid (FFA), and b-hydroxybutyrate concentrations during exercise. However, mean serum glycerol concentrations were significantly higher [indicating mobilization of fat stores with glycerol release] in the HFD-CHO trial. The HFD-CHO diet increased total fat oxidation and reduced total CHO oxidation but did not alter plasma glucose oxidation during exercise. By contrast, the estimated rates of muscle glycogen and lactate oxidation were lower after the HFD-CHO diet. The HFD-CHO treatment was also associated with improved time trial times (29.5±2.9 min vs. 30.9±3.4 min)[150 min cycling at 70% vO2-max followed by a 20 km time trial] for HFD-CHO and CTL-CHO. They conclude that “high-fat feeding for 10 days prior to CHO-loading was associated with an increased reliance on fat, a decreased reliance on muscle glycogen, and improved time trial performance after prolonged exercise”;
Leddy et al., “Effect of a high or a low fat diet on cardiovascular risk factors in male and female runners,” Med Sci Sports Exerc. 1997 Jan;29(1):17-25, which notes that “restricting fat intake may compromise endurance performance and that increasing fat intake may improve endurance performance,” and concludes that “a 42% fat diet maintained favorable CHD risk factors in female and male runners whereas a 16% fat diet lowered Apo A1 and HDL-C and raised the TC/HDL-C ratio”;
Horvath et al., “The effects of varying dietary fat on performance and metabolism in trained male and female runners,” J Am Coll Nutr. 2000 Feb;19(1):52–60, which concludes that “runners on a low fat diet consume fewer calories and have reduced endurance performance than on a medium or high fat diet [and] a high fat diet, providing sufficient total calories, does not compromise anaerobic power.”
Monday, October 6, 2008
We’ve been reading about nutrition and making our own dietary decisions based on that reading and our personal experience for about nine months now—hardly long enough to become real experts, but long enough to have developed our own best guesses as to what seems to be right, at least for us.
So here is “David and Cynthia’s Guide to Low-Carb Eating.” Basic principle: cut back drastically on the simple starches and sugars that have become ubiquitous in first world diets (of all ethnicities and nationalities). Period. End of story. Beyond that, the details are secondary and serve mostly to provide guidance as to how to achieve that goal. Some details also have secondary health effects that are important if still secondary.
First, of course, you need to recognize what the major dietary sources of simple starches and sugars are. Sugar would seem to be obvious, but there is a large misinformation campaign out there on the part of advocates of various sugar substitutes that can trip up the unwary. A simple rule of thumb is that if it tastes sweet and isn’t a non-nutritive sweetener (sucralose, saccharin, aspartame, etc.), it’s sugar and needs to be minimized in your diet. Calling it “evaporated cane juice” is just a silly marketing ploy. Honey, rice syrup, maple syrup, etc. may have additional valuable trace nutrients, but the macronutrient is still sugar. Even maltodextrin, which is a long-chain sweet-tasting molecule, that gets classified as a starch instead of a sugar, is still readily broken down by the body to simple sugars (that’s why it is added to sports drinks and “gels”). Don’t be fooled by “100% juice” products and similar products with added fruit juice that use apple, pear, or white grape juices to provide sweetness. These are just alternative sources of sugar; apple and pear are particular bad in that they contain a high percentage of fructose. If you must sweeten your food, use whichever of the artificial sweeteners that you tolerate the best. We don’t really like any of those that we have ready access to and generally opt to simply make do with a lot less sweet taste in most of what we eat, but we do use Splenda (maltodextrin and sucralose) when we feel we need a sweetener. (There are at least a couple of potentially better non-nutritive sweeteners with less objectionable taste and aftertaste: Stevia-based products like Truvia and Acesulfame-Potassium-based products like Sweet-One. These sound promising in written descriptions, but we haven’t yet tried them and don’t presently know where to buy them affordably in bulk. Ordinary table sugar and high-fructose corn syrup remain the sweeteners that are commonly sold at much the lowest net price [price per unit of sweetness].) You also need to limit your intake of fruit, especially juices and dried fruits which tend to encourage large servings. All fruits contain significant amounts of sugar in addition to all the nominally healthy micronutrients (vitamins and minerals) that they are often advertised to contain.
Simple starches include starches from grains and tubers. Most ubiquitous in the American diet is wheat starch (flour, bread, etc., etc.). Rice, oats, barley, quinoa, rye, and other grains aren’t much better (despite the advertised heart-healthy characteristics of oats, for example). Potatoes are the most common tuber with a lot of simple starch. These starches are quickly broken down by the body into simple sugars.
Other foods also contain carbohydrates. Many vegetables contain significant amounts of carbohydrates as either starches or sugars or both. Root vegetables such as carrots and legumes such as peas and beans tend to contain more carbohydrates than leafy green vegetables (spinach, kale, lettuce, etc.) and cruciferous vegetables (broccoli, cauliflower). However, for the most part, you are much less likely to overeat starches from these vegetables, and you get plenty of other good nutrients. On balance, we don’t think you need to particularly avoid the higher-carb vegetables, although some recommendations such as those for the “induction phase” of the Atkins diet, have you minimize their consumption as well.
Dairy products contain carbohydrates too. Lactose is a disaccharide of glucose and galactose, and a typical 8 oz serving of milk or yogurt contains 9 to 17 g sugars (depending on how much dry milk was added or how much fermentation occurred). Hard cheeses generally contain much less carbohydrates. Casein is reputed to induce insulin release, which of course defeats the purpose of the low carb diet: to minimize blood insulin as well as glucose, so that the fat cells are releasing fat for use as fuel, rather than sequestering it safely away for long term storage (making us fatter). But that doesn’t stop us from using dairy products which also contain a lot of protein and fat; we aren’t interested achieving zero carb intake or in seeing how fast we can lose weight, but rather in eating a diet that we can sustain indefinitely to reach our target weights and maintain it, without giving up in screaming frustration and deprivation. We like our dairy products! Curiously, the “paleo diet,” which is a fairly low carbohydrate diet, proscribes dairy products but encourages consumption of a lot of fresh fruit. We remain skeptical of such a recommendation unless you happen to be lactose intolerant.
You probably shouldn’t try to cut out all carbohydrates. How low you need to go to be practicing a “low-carb” diet is something that is not well understood. Our own feeling (read “guess”) is that there is no magic threshold, and the answer may vary widely from individual to individual. Certain individuals seem to be able to thrive on a high-carbohydrate diet for a lifetime, while others clearly do much better on much lower levels of carbohydrate consumption. It probably depends on both your genetics and on how active a lifestyle you lead. For us, cutting carbohydrate consumption to under about 20% of calories seems to work well. Some studies have shown significant benefits of lesser reductions. Others advocate more extreme reductions in carbohydrates. If your goal is to get under 20%, then you don’t need to worry too much about starches in vegetables, and it’s even OK to “cheat” a bit. Go ahead and eat some sweet dessert occasionally or even eat that piece of pizza at the party where no low-carb alternatives are offered. Just try to keep the averages down.
The Atkins organization recommends starting out a low-carb diet with an ultra-low-carb induction phase (less than 20 g per day) for a couple of weeks followed by a low-carb phase which is then further relaxed after target weight levels are reached. We don’t see any clear evidence that such a phased approach makes any particular sense or has any particular benefit other than shock value and initial rapid weight loss to keep motivation high. It may be true that the abrupt change induces fat adaptations more quickly, but we know from studies that it takes at least 2 weeks to biochemically adapt (see Phinney (2004)), and a more gradual adaptation may be less stressful for some people. It seems simpler, and probably just as effective, to simply change to a new long-term diet and stick with it. Too many people treat the Atkins diet as a temporary weight loss diet that can be abandoned after the weight loss is achieved. These people regain much or all of the weight lost. It’s not clear that repeated Atkins inductions are as effective either.
A couple of further remarks on types of carbohydrates are worth making. First, we reiterate the important difference between fructose metabolism and glucose metabolism (see our earlier blog entry on fruit). While fructose produces a lower glycemic response, it’s probably a lot worse than glucose from a weight management point of view. Most sweet foods, including most fruits, actually have about equal amounts of fructose and glucose, so there’s not a lot you can do to minimize fructose in favor of glucose, but if you do have a choice, don’t go for high-fructose foods.
Fructose is metabolized by the liver into triglycerides which are then easily stored as fat. The path from glucose to fat is at least a little more convoluted, but it’s clear that triglycerides track carb intake, a fact that is shocking to most people since we’ve been taught that fat intake is what drives triglyceride levels high. However, this is not so: ingested fat is transported in chylomicrons and is preferentially absorbed by the body tissues, and so disappears from the blood quickly (within an hour typically). Triglycerides, in contrast, are produced by the liver in response to fructose and carb ingestion and released into the circulation for hours after each carbohydrate containing meal. Hence high carb meals result in all-day (and all-night) elevated triglycerides. That’s why people on low carb diets have very low triglyceride levels compared with people eating “normal” high carb diets, despite proportionately higher fat intakes (see, for example, Table 3 of Gardner et al., 2007 and Parks and Hellerstein 2000).
Second, certain starches have come to be known as “resistant” starches that are metabolized more slowly and generate less of a glycemic response (blood glucose spike). For the most part, these are the vegetable starches, and perhaps most importantly, the legumes, in particular. This provides a justification for the standard practice in low-carb cooking of replacing grain flours with legume flours such as soy flour or chickpea flour. These bean flours have less carbohydrate than wheat flour, but still have significant amounts. The fact that the starches in beans are digested more slowly seems to make them less prone to producing a blood glucose spike and less prone to being converted to stored fat. Speaking from personal experience, this substitution works quite well, at least from a nutritional point of view. You can do a one-for-one substitution of soy flour for wheat flour in many recipes. Those foods (like bread) which depend on wheat gluten to provide mechanical strength (elasticity) to a dough don’t work too well with a 100% substitution. In these cases, we use part soy flour and part gluten flour (wheat gluten separated from the wheat flour—use about ¼ to ⅓ wheat gluten by volume). Wheat gluten is mostly protein and is safe to use in low-carb cooking (unless, of course, you happen to be sensitive or allergic to it). You can also effectively substitute fiber such as wheat or oat bran and almond meal or other grated nuts for part of the flour.
What about “whole” grains and fiber? Don’t we need a lot of fiber in a healthy diet? Aren’t whole grains good for you? Not as far as we can tell! And we have no personal bias against whole grains. We like to eat them. Our current best hypotheses regarding whole grains and fibers:
1. To the extent that fiber is good for you it is in the context of high-carbohydrate diets only. If nothing else, adding fiber tends to fill you up with more non-nutritive filler, and you eat less simple starch.
2. Fiber probably also promotes intestinal health in the presence of a large carbohydrate load in the gut. Without the large carbohydrate load, it is less clear that you actually need a lot of fiber. Populations that eat no carbohydrates manage just fine with little or no fiber.
3. The alleged binding of starch to fiber to slow starch metabolism seems to be a myth. The measured glycemic response to whole grains is identical to that of equivalent amounts of refined grains. Perhaps if you swallowed genuinely “whole” grains that are still fully encapsulated in fiber (don’t chew!), you might slow the starch metabolism, but otherwise the starch you do consume is still processed quickly.
4. You may get more trace nutrients from whole grain than from refined grain, but there are better sources for those trace nutrients.
5. The same goes for fruit! Fruit contains a lot of fiber and significant trace nutrients, but it comes with too large a dose of sugar.
6. Fiber is not completely non-nutritive. It is at least partially digested by bacteria in the intestines, and seems to lead to production of short chain fatty acids, which are absorbed to varying extent. What that means nutritionally, I’m not sure. There’s probably not enough net usable calories in fiber to be of much significance. On the other hand, the short chain fatty acids are elongated in the liver to increase the net triglycerides.
7. If you want to eat fiber, go ahead! Focus on vegetable sources which come with a lot higher doses of trace nutrients anyway. It’s probably OK to add wheat or oat bran to your baked goods, but do it because you like it, not because it makes you feel virtuous. But be aware that sources of phytic acid such as grains are known to reduce absorption of minerals and may contribute to osteoporesis and other deficiencies.
8. There aren’t any significant nutritional differences between soluble and insoluble fiber that we’ve been able to identify.
9. When you read nutritional labels, “total carbohydrates” generally include any fiber in the food. It’s probably OK to subtract out the fiber as being largely non-nutritive. But beware of claims of “zero net carbs” or similar for foods that obviously contain simple starch. You can only subtract the fiber content from the total carbohydrate content to the extent that the total includes the fiber in the first place. You can’t add fiber to offset the presence of simple starches.
What about fuel for exercise? Don’t athletes need carbs to provide short-term fuel for peak performance? Probably not! This one is fairly complicated to sort out in detail, though. If you are accustomed to a high-carbohydrate diet and switch, you will likely feel that you can’t get peak performance or even satisfactory performance from your muscles for some period of time while the body’s endocrine system and metabolism readjusts to use the fuels you do provide. For instance, there is evidence that a high fat diet increases mitochondrial biogenesis (through activation of PPARdelta) and induces muscle type switching from fast twitch to slow twitch (from glycolysis to fat burning), and importantly, may induce resistance to obesity. This adaptation period of time may last for 2–6 weeks depending on your particular circumstances, but you will get through it and eventually find that you can switch over to fat burning. The evidence supports low carb diets for endurance sports at least, as fat burning enzymes and mitochondria are increased resulting in carb sparing for when you really need it. Is “carb loading” before competition useful? Probably not, again! Making sure your muscles are fully loaded with glycogen may be valuable for maximal anaerobic efforts and sprints, and possibly for longer events, but do it by tapering your training, not by carb loading. What about right before or during the event (especially for events of more than 2–3 hours duration)? This one is less clear. It’s possible that you can achieve a personal best performance with the aid of some extra quick-release fuel from carbohydrates, but even that could be a myth. While we find that, now that we are adapted to low-carbohydrate-fueled exercise, we can go longer without any refueling, but we still eventually need to refuel. We still tend to use carbohydrates, because that’s what’s usually available. But we do try to avoid or at least minimize the simple sugars and make sure we get some protein and fat, too. We haven’t yet tried to maintain a high level of exercise over periods of more than four hours using mostly fat or fat and protein as fuel. Right now, we’re inclined to think it will work just fine, although it may be necessary to start refueling a little sooner to compensate for slower digestion. Post-event nutrition is important, too, but the key need then appears to be added protein to speed muscle repair and recovery, not carbs.
So then, if you’re not eating carbs, what do you eat? The short answer is fat! While you may not have been eating enough protein on your high-carb diet, it’s pretty hard to replace carbs with only lean protein, and can make you sick (the liver can’t dispose of that much ammonia). As a practical matter, a low-carb diet is almost always a high-fat diet. Anyone who tries to have it both ways by continuing to recommend restricting fat consumption while supporting reduced carbs is deluding themselves. It’s essentially a prescription for extreme total calorie restriction, and no one should maintain severe calorie restriction for more than very short periods (and probably not even that).
What kind of fat should you eat? That’s a much harder question, and we think it will be a few years before we have a good well-researched answer. From a simple macronutritional point of view, it appears that it probably doesn’t matter too much. It’s much more important to your health that you replace calories from simple sugars and starches with calories from fat than that you carefully choose which fats to eat. That’s the curious thing about how the popular press and the attention of the public at large focus on nutritional issues. Millions of people will start taking the latest supplement based on flimsy evidence that it slightly improved some condition or other in a handful of test subjects while completely ignoring the basic macronutrient imbalance in their diets. We will take the micronutrient research a lot more seriously when we finally get the macronutrient recommendations properly understood and straightened out.
That said, it is worth commenting on what some of the major issues are with regard to fat choices. Most obvious, of course, is the saturated fat controversy. As nearly as we can tell, there is no good scientific evidence that saturated fat is bad for you despite decades of pronouncements that it is. (This subject is too big and too controversial for one or two references; perhaps we'll write more about it in the future.) Higher consumption of saturated fat may be correlated with elevated blood lipids (particularly HDL, but that's "good" right?), but those elevated blood lipids are not well-correlated with health problems such as coronary artery disease. The assumption that saturated fat is bad is so ingrained in the culture and training of our “experts,” that one must read all related studies very critically, and understand that in the presence of excess carbohydrate, triglycerides will be elevated in most people, and will be formed primarily of saturated fat. You often find that authors are struggling to reconcile apparently contradictory results with the assumed “truth” that saturated fat is bad. Looking critically at the actual data often shows that, if there is any clear difference at all, the test subject consuming more saturated fat were better off on whatever measure was being monitored. So go ahead and enjoy your butter and meat fats, but limit the carbs when you do. Use lard if you like.
For a while we were taught that the more unsaturated a fat was, the better. Then we learned that omega-6 polyunsaturated fats are bad and so maybe monounsaturated fats were as good or better. Hydrogenated vegetable fats were initially considered a “healthy” substitute for the evil lard and butter, but were later found to be worse. “Trans-fats” have recently become taboo. More recently, there is concern that polyunsaturated fats are easily oxidized and implicated in inflammatory atherosclerosis processes ("oxidized LDL"). We are now focusing on the relative amounts of omega-3 and omega-6 fatty acids in our favorite fats and our overall diets. So what’s a high-fat eater to do? In the absence of good science, we still have to eat! Here’s our current working recommendations and hypotheses (aka best guesses):
1. Go ahead and eat as much saturated fat as you like. It won't become oxidized and will increase HDL levels.
2. Avoid trans-fats and hydrogenated vegetable fats.
3. We tend to favor olive oil, then canola oil, then nut and seed oils in our cooking right now, but we’re open to new data that might shift the emphasis around. We've been tempted to try the rendered goose fat available in our local market, but haven't yet. We’re likely to choose an oil based on its performance or taste characteristics as much as anything and to favor cheaper oils when performance or taste don’t dictate a clear choice.
4. Omega-3-rich fats and oils are probably desirable when and where you can get them. Wild oily fish such as salmon and mackerel are probably the best sources. (Farmed fish may not be, depending on the feed that is used.) If you want to go with supplements, use fish oil or cod liver oil by preference over flax seed. Flax seed and flax seed meal or oil are probably the best readily available vegetable sources of you prefer them or want to use them in addition, but it’s not clear how much of the omega-3 fats in flax are even converted in our bodies to the desirable forms.
5. “Free-range” and “grass-fed” meat probably has “better quality” fat than the factory or feed-lot (corn-fed) equivalent. You may also find that it tastes better. It’s also typically a lot more expensive if you’re not raising your own. If your budget allows, and your local stores offer it, by all means go for it, but don’t worry too much if you find yourself eating mostly the cheap stuff.
Getting the macronutrients generally right is still the most important thing to do. Since fats become a dominant source of nutrition in a low-carb diet, it is apparent that the choice of which fats to eat must become a close second. Absent clear scientific evidence to support a strong emphasis on one or two sources of fat, the best we can conclude for the moment is that you should diversify and consume a least some fat from a lot of different sources.
So what about protein? It’s pretty clear that you do need some protein, and in particular, you need protein that contains certain “essential” amino acids that the body cannot manufacture for itself, including vitamins such as B12 that are difficult to find anyplace else. Animal protein (especially organ meats) is a very rich source of most vitamins (except folic acid and vitamin K). Chronic protein and vitamin deficiency can cause severe malnutrition, poor muscle development, and premature aging. Vegetarians need to be particularly careful since good vegetable protein sources tend to be limited and tend to have much lower protein and vitamin content than meat and fish. From a purely nutritional point of view, humans aren’t really designed to be vegetarians, though if you choose to be so on moral or religious grounds, it is still possible to avoid malnutrition as long as you make sure you get enough of the right proteins and supplement to avoid vitamin deficiencies.
You will also find warnings against eating too much protein, particularly if you have impaired kidney function. For most people, this is not a serious concern in that it’s fairly difficult to actually eat too much protein. (See, for example, Martin et al. (2005).) Perhaps, if you tried to cut both carbs and fat out of your diet, then you could do it, but most reasonable ad libitum diets emphasizing fat and protein are not likely to give you too much protein.
Obviously, there’s no good reason to follow the low-fat crowd to the leanest cuts of meat. You don’t have to remove the skin from chicken and turkey of you don’t want to, and go ahead and leave your beef, pork, and lamb untrimmed if you like the fat. You can also eat cheese and other dairy products for protein as well as eggs, nuts, seeds, and tofu. These tend to come with a generous serving of fat, but that’s OK.
If you’re an athlete, then you may need to consciously increase your protein intake to help build and repair muscle. If you have trouble getting enough protein from your standard dietary sources, you can supplement by using either whey protein or soy protein powders. Whey protein is probably the better choice from a protein quality point of view, and there is some concern that soy protein, if consumed in large quantities, may provide excessive hormones. We use both with an emphasis on the whey protein. Whey protein tends to be sticky and gooey (at least when concentrated), and soy protein isolate behaves more like a flour; both are largely tasteless by themselves. They can be added to anything from eggs to baked goods and drinks. They are often packaged for retail sale in various adulterated (and overpriced) forms with added flavorings and sweeteners. Buy them unadulterated if you can (one on-line source: Honeyville Grain).
One last useful ingredient that we recently discovered is polydextrose. This is a long-chain sugar polymer that is largely indigestible and functions nutritionally like fiber. It is also tasteless (i.e., not sweet by itself). However, it can provide a lot of the mouth feel and body that artificial sweeteners generally fail to do. So far, we’ve tried it in homemade artificially sweetened ice cream and carrot cake with very satisfactory results. (You may need to disperse it in warm liquid first; it tends to clump.) We never met a low-fat ice cream that we thought was worth eating, but as long as you use flavors that adequately mask the objectionable bitterness and aftertaste of your artificial sweetener, you can make a very respectable low-carb ice cream! You can buy polydextrose as a commercial food ingredient, for example, from Honeyville Grain.
We find we don’t really miss most carbs. We don’t crave things like cookies or noodles at all, but occasionally find it necessary to eat a sweet potato or make polenta to quiet the cravings for a few days. It also depends on how much we are exercising. Of late, with our 50+ per week running mileage, it seems less important to cut carbs, but we generally keep them low anyway, compared to the usual endurance athlete's diet). On the other hand, the more we exercise, the less the weight comes off! We're not sure if it's due to eating more carbs or increased cortisol levels from overdoing it of late (three 50K trail races since Aug 23 and a 50 miler planned!).
Monday, September 1, 2008
We are generally strictly recreational runners. Cynthia ran a few marathons some 20 years ago; the longest races that David ever entered competitively were a few 10K events (plus a sprint triathlon), though we’ve also both done quite a bit of race organizational work. On something of a whim, we completed our first 50K race last weekend. The race was in the Marin Headlands, north of San Francisco. It was probably not the best choice for a first 50K, since it involved serious hill climbing (about 7000 ft of total climb spread out over seven “hills”) and rough trails. We were probably not as well prepared as we should have been for such an event, but figured if we could do 18 miles over similar terrain, we should be able to struggle through another 13 miles if determined and prepared for blisters.Our basic aim was to complete the event in reasonably good condition, and we succeeded admirably, if not speedily, coming in at about half the pace of the first finisher, and very near the back of the pack. Not surprisingly, the last half was more an exercise in keeping going than trying to achieve any speed at all—we walked up all the hills and jogged pretty slowly on the way down. However, we were still mobile at the finish line and had no major injuries or problems. We took two days off and were able to run one of our standard hour-and-a-half hilly runs, feeling, if anything, stronger than usual the third day. On balance, except for the slow pace, we were pleased with our success.
Just so as not to blame our low carb diet for any difficulties, we had a pasta dinner the night before in the traditional “carb loading” style of runners everywhere, and even ate oatmeal for breakfast before the race began. (As it turns out, Cynthia felt worse than usual, whether that was due to the early hour and lack of sleep the night before or to the change in diet, we don’t know.) And of course we tapered our training the couple days before. One advantage of running in an organized race is the periodic aid stations, where you can load up on water, electrolytes, and food such as potatoes, cookies, chips, PB&J sandwiches, so you don’t have to carry liters and liters of fluids and snacks with you.There were many with the usual runner physiques, slim and wiry, and quite a few older runners, some significantly older than we are, some distinctly overweight, but in strong physical condition nonetheless (better than us it turned out). Certainly many of the people interested in these long events tend to be those that are good at it, with some inherent natural speed and talent. But you don’t have to be inordinately talented to enjoy a long walk/jog through the woods, communing with nature, or challenging your own talents.
The course was every bit as difficult as promised, and about half way through, after the first three monster hills, Cynthia felt “bonked”—low on energy and wondering how to eek enough effort out of her tired legs to get through the rest of the event. In fact, Cynthia thought it was far more difficult than any of the street marathons she ever did—those resulted mainly in increasing pain in the legs and feet, and less of a sense that she could not continue due to the low energy or the weight of her legs. And it took more than twice as long as any marathon she had ever run! A serious testing indeed. Even her lungs feel fried days afterwards.Description of the event can be found in an article in the Marin Independent Journal, as well as Jean Pommier’s fartherfaster blog.
David clearly was better prepared to maintain a higher level of energy output and likely could have gone significantly faster, but we stayed together for safety, support, and companionship. The fabled Headlands fog never lifted and the cool sea breeze was a blessing. Cynthia doesn’t think she could have made it in normal summer heat. The volunteers were wonderful and supportive: Many thanks!But the interesting story is really our observations on energy intake and expenditure. Cynthia was reluctant to start eating at the aid stations, because the lump of breakfast hadn’t even passed yet, and why should she need more carbs when the oatmeal was still digesting? She did go for juice and chicken broth (a favorite for cutting hunger pangs and preventing nausea) and a bit of sandwich, but she didn’t feel that anything coming in made much of a difference, except perhaps to allow her to keep going, albeit at reduced pace. And perhaps that is enough, to keep going when fatigue, nausea and assorted pains would otherwise make you stop. We estimate that Cynthia’s total caloric intake during the race was only about 800 kcal—She has never been good at eating while running. We think she drank enough to stay hydrated—not too difficult in the cool conditions.
David’s approach was quite different: he’d quickly down a couple of gels (at 100 kcal each), a couple pieces of boiled potato or bit of banana at each aid station, and drink a couple of pints of sports drink and/or water over the distance between aid stations (about 4 miles apart). His total intake during the race is estimated at more like 3000 kcal.We attempted to estimate the energy expenditure (as excess over basal metabolic rate) required to complete the race. We did this a couple of ways based on published values for running and walking on the level, and some information on the food energy intake required to sustain a certain level of mechanical work output (you need about 4 kcal of food energy in for every 1 kcal of mechanical work). Our rough estimates are that Cynthia burned about 3500 kcal, and David burned about 4500 kcal during the race. (It felt like a lot more!)
Of course, in addition to the food consumed during the race, we ate more than usual before and after the race. All told, Cynthia consumed about 1000 kcal more than typical, and David consumed about an extra 3000 kcal. If these numbers are anywhere close to correct, Cynthia ran a net deficit of about 2300 kcal, and David a net deficit of about 1500 kcal. Conventional wisdom is that it takes a net surplus/deficit of 3500 kcal to gain/lose a pound of fat, so a strict energy-in-minus-energy-out-equals-energy-stored-as-fat model would suggest that we should each have lost some measurable weight (but under a pound) once we were back to steady-state hydration levels (i.e., by the next morning or so).So what really happened? Our weights were up a pound or so on race morning (presumably from carb loading the night before). The next morning, David’s weight was up another four pounds; Cynthia’s weight peaked the second morning after, up about three pounds from pre-race levels. Thereafter, the weight came back off over 4–5 days, returning to previous trendlines. The gain was particularly rapid, although the loss was also very rapid if looked at out of context.
Even though we don’t believe in the energy-in-minus-energy-out-equals-energy-stored-as-fat model, we were still surprised to see such a dramatic weight effect and especially to see a significant temporary weight gain as a result of the event. So why did our weight increase? Maybe muscle and ligament damage from overuse results in temporary swelling and fluid retention due to inflammation? Maybe the body fears that you’re going to go out and get dehydrated again, so compensates with some hormonal signals to retain additional fluids? Our appetites were elevated substantially for a couple of days, but not enough to account for the weight gain. Is it psychological or physiological? What about growth hormone and insulin levels after endurance events? Or some other hormone levels? Or were we just seeing the results of a spike in carbohydrate consumption and the consequent increase and decay in carbohydrate-induced fluid retention? (The correlation between carb intake and some amount of increased fluid retention is well-known, particularly in the context of initial weight loss when starting a low-carb diet, although it is less well understood exactly where and why all the increased fluid retention occurs or what the time-constants associated with diet changes should be.)A week later we ran one of our longer routes—about half the length and time of the race—consuming much more modest total calories in general and carbs in particular. Knowing what to look for, we saw a modest increase in weight the next morning (a pound or so, and more or less within the noise of normal daily fluctuations).
The bottom line? We clearly can’t recommend endurance running as a weight loss aid. One, the energy consumed is just too small!!! It may feel like you’re burning off huge amounts, but the fact is, our bodies are quite efficient, and can perform large quantities of work using modest amounts of fuel. Two, while it is easy to end up with some calorie deficit, it is difficult to do so in a measured and controlled way—the tendency is to overcompensate for a perceived expenditure and negate any losses. Three, with more strenuous expenditures, there is a need to replace not just calories, but also vitamins, protein and electrolytes, etc., to heal injuries and strengthen bones, ligaments and muscles, and restricting food can lead to exhaustion if not serious injury and illness. Four, at least in the short run, there appears to be compensatory fluid retention and weight gain, so don’t think you can go out and burn off a pound of fat in a day and thereby fit into that dress you want to wear!
While, in general, serious endurance athletes report being able to eat more or less unlimited quantities of whatever they feel like eating, more casual or occasional endurance efforts aren’t going to have much effect, and may even tend to show weight gain instead of loss, especially if one erroneously believes one is burning off fuel in excess of actual needs. That said, we did find the experience to be a positive one overall, given our incoming level of fitness (i.e., we weren’t attempting anything too far outside of our level of fitness). We recovered quickly and felt, if anything, stronger and fitter afterwards. We stayed within the recommendation that, when first attempting longer and harder events, one should first just aim to finish and become “comfortable” (or at least, familiar) with the new distance, then try to do it faster. We're still working on it, but further gains may have to wait until we’ve dropped down to more of an optimal weight, and until we’ve undone various metabolic and/or structural damage due to poor eating habits over many years (assuming our present diet is doing so)!
Sunday, August 17, 2008
At the beginning of 2008, I adopted a non-calorie-restricted low-carbohydrate diet. If anything, I reversed the Atkins-recommended pattern of an “induction phase” of extremely low carbohydrates followed by a maintenance phase. Rather, I phased out carbohydrates from a previous life of 60% carbs (10% protein, 30% fat) to more like 15% carbs (25% protein, 60% fat) over a month or so by slowly finishing off leftover holiday sweets and breads and then not replacing them. Eating to satiety also occurred with an estimated total daily calorie reduction from about 2700 to about 2100 (all very rough numbers). The resulting weight loss is shown on the graphs of weight versus time (date).
I saw an initial weight loss rate of about 2 lb/wk for the first 2–3 weeks, similar to a typical induction phase. Thereafter the rate of loss dropped off to about 1 lb/wk, slowing perhaps to 0.75 lb/wk. It was starting to look like a possible exponential decay from an initial state to a final state resulting from a step change in diet, with a time constant of 8–14 months depending on what I chose as a likely asymptote. (Until there is measurable curvature in the data, it’s not possible to reliably fit a specific value to the asymptote.) I was trying to model the weight loss as a simple exponential decay, assuming that there was a single step change to account for. This would result in a linear fit on a semi-log plot of weight above assymptote versus time. This exponential approach to an asymptote (slowing of weight loss) might be expected because as body mass decreases, less total caloric intake is required just to maintain the body’s metabolic needs. Without further modifying the diet to decrease calories in, one would expect the weight loss to slow. You can see on the graphs that the data could be fit nicely to either an exponential model (straight line on the semi-log plot) or to a piece-wise linear model (set of straight lines on the linear plot) through July. The exponential fit shown assumes an asymptote of 165 lb. The linear plot has the exponential fit shown in orange. The light blue linear fit is drawn through the data from about February through May. The green line is a piece-wise linear fit with segments for the first two weeks, then mid-January through mid-March, mid-March through July, and a separate line for early-July through mid-August. The dashed dark green lines delimit a ±2 lb tolerance band about the mid-March through July fit line.
By mid to late July, it was still difficult to clearly identify which model fit the data best given the normal daily scatter in the data (even with some care to always measure under the same conditions, first thing in the morning). Certainly, a piecewise linear model where there was presumed to be some sort of “induction” phase for the first couple of months followed by a slower linear weight loss rate thereafter fit the data at least as well as the exponential fit.
Then, around the beginning of August, I was starting to get a cluster of data points that were looking unusually low, even though I hadn’t specifically made any major change in diet or lifestyle that I was particularly conscious of. Now, in mid-August, looking back, one can model the last six weeks of data as exhibiting a linear loss of about 1.5 lb/wk, about double what it had been for quite a while! So much for any simple linear or exponential fit to the data! Where will it go from here? And why? I’m not at all sure. Stay tuned for the next exciting episode!
I probably also eat somewhat less as my weight has decreased, although since I haven’t been keeping a careful food diary, that’s hard to prove. It’s clear that eating more dense calories helps you adjust to eating less food total, since you achieve satiety with smaller piles of food on your plate and fewer second helpings.
So, what’s going on in my life besides the low-carb diet? What could have caused the weight loss to accelerate? Clearly, life is more complicated than simple step changes and rapid return to a new equilibrium or steady-state.
A couple of things that may be different in the last 6 weeks with respect to diet are that I am probably eating a smaller late evening meal (meaning usually no second helpings), and about 3–4 days per week, my breakfast is now a protein shake, consisting of a couple of cups of whole milk with soy protein and/or whey protein plus low-caloric flavorings. My best estimate is that the number of calories in that breakfast is about the same as the typical cheese omelette or similar that I often eat otherwise, but there probably is a shift toward more total protein and less fat in the meal.
I’m now down about 30 lb in 33 weeks. I expect to be able to comfortably lose at least another 10 if not 20–25 lb before I reach a stable healthy weight. I suspect that I have more upper-body musculature than I had in my 20s, which may limit me from reaching my minimum athletic college weight, but I’m not sure. My waist circumference was about 34" in college, increasing to about 38" until recently when it got up to about 41". I’m back down to 36" now, and still have a little bit of a “spare tire.” I expect to get back down to 34". Almost all of my excess weight seems to have been stored as visceral fat in the abdomen and above the beltline for most of my pants—none of the weight gain or loss ever made all that much difference to the fit of most of my clothes, one of the reasons that my pattern of weight gain was rather insidious and easy to ignore. (This is probably true for most men.) Many of the symptoms of metabolic syndrome that I had have now gone away or abated (more on that after the next physical exam.)
Part of what had resulted in the relatively rapid weight gain in the last 2–3 years were some major changes in my life that made me more sedentary after a period of higher activity, along with an appreciative eating audience who enjoyed and encouraged my baking habits. (We have yet to find or develop a new bread recipe that is an acceptable low carb substitute, though we’re making progress.) One always tends to reduce eating more slowly than one reduces activity, so in principle, the weight could have accumulated simply because of excess calories. (Or was it excess carb consumption?)
In the last few years, I have eaten more of my calories late in the day, if that makes any difference. (I think it did, if for no other reason, than because I was more likely to need extra snacks to hold me until a late evening meal. Previously, I ate an earlier dinner, so I didn’t need an afternoon snack, and rarely ate anything for several hours before sleeping.) But I was hardly leading a couch-potato lifestyle while gaining weight. I was typically running at least 25–30 mi/wk on hilly terrain, if not always very fast. The running certainly seemed to be getting harder as I got either older or heavier or both. For my weight (averaging about 210 during this time), this amount of exercise should translate into 3300 kcal expended each week, or an average of 472 kcal/day (assuming no additional caloric expenditure for the hills—my best estimate is that our particular hills added another ~60 kcal/day). I estimate I was eating an average of about 2700 kcal/day during this time, which is about as much as the Runner’s World diet page says is needed to maintain my weight with only light exercise. Without getting into a critique of the Runner’s World diet recommendations (another posting), I should not have been gaining weight on this amount of calories with the amount of exercise I was getting!
Not surprisingly, my running ability has improved significantly with 30 fewer pounds to cart around. My breathing is easier and slower. My heart rate is slower and recovers faster. I can run uphill again, where I previously pretty much slowed to a walk most of the time. Longer runs (12–18 miles) don’t wipe me out anymore. I’m probably logging closer to 40 mi/wk than 30 mi/wk right now, though I’m still not going to win any races.
Regardless, what I am doing works! I’m not struggling at all to lose weight. I never feel like I am starving myself, and except for the usual carb temptations in the world at large, I am finding the diet easy and comfortable to live with and sustain.
Wednesday, July 30, 2008
A friend sent me a link to this just published article about weight loss and exercise. According to the abstract of the actual scientific paper (I couldn’t access the full text), overweight and obese women (201 subjects, aged 21–45 years with BMIs from 27–40) were assigned to 1 of 4 behavioral weight loss intervention groups. They were randomly assigned to groups based on physical activity energy expenditure (1000 vs. 2000 kcal/wk) and intensity (moderate vs. vigorous). Participants also were told to reduce food intake to 1200 to 1500 kcal/d. (Doesn’t sound to me like an easy caloric intake to achieve on any of the usually recommended weight loss diets.)
According to the abstract, weight loss did not differ among the randomized groups at 6 months (8–10% of initial body weight) or 24 months (5% of initial body weight) follow-up. (In other words, calorie restriction on whatever diet they were using was not sustainable; or starvation is not fun!) Post-hoc analysis showed that individuals sustaining a loss of 10% or more of initial body weight at 24 months reported performing more physical activity (1835 kcal/wk or 275 min/wk) compared with those sustaining a weight loss of less than 10% of initial body weight (P < .001).
The authors concluded that the addition of 275 mins/wk of physical activity, in combination with a reduction in energy intake, is important in allowing overweight women to sustain a weight loss of more than 10%. They also concluded that interventions to facilitate this level of physical activity are needed. In other words, the current recommendations for exercise to achieve and maintain weight loss are not nearly enough—at least not as currently practiced.
We couldn’t resist posting our own observations about weight loss and exercise. From the female perspective:
Back when I was a wee lass (in college), I recall weighing myself in the locker room after a tough workout for the crew team, and weighing in at 120 lbs. My usual weight was probably more like 125 lbs. (It sure would be easier to sprint up the stadium steps at 125 lbs than my current weight of 150 lbs!) I don’t know for sure whether there was any weight change as a result of crew training, but I remember eating enormous amounts during spring break when we worked out three times a day! Crew workouts can easily spend energy at the rate of 1000 kcal/hr (though few could keep up that pace for very long).
Then in my mid-twenties, I jogged a lot and ran several marathons. I didn’t train excessively—I probably logged 35+ miles per week, with occasional longer weeks when preparing for longer distance events. It helped me deal with stress and improved my confidence and self-image. Overall, jogging was a good thing for me, though I was never fast. (I almost qualified for the Boston marathon once, but got injured and had to slow down-- I could never be a world class athlete). I was thin then, but not skinny. I don’t recall even having a scale then, so I have no data on my actual weight (though I still have some clothes from that era, which currently do not fit). I remember, in particular, a friend asking if I was having any menstrual cycle disturbances from all this running, and I replied no. He felt my arm and said something like “of course not” in a derogatory voice, meaning I was way too fat for that. Did I say friend? I meant obnoxious jerk!
At any event, I was slim, healthy and strong (relatively), looked better than ever, and ate plenty of carbs (although I recall eating mayonnaise straight out of the jar once after a long run I was so starving!) I was also single, and that I think turns out to be the real kicker here. At least for me, I am less likely to eat well when eating alone. Conversely, I tend to overeat at times when eating with friends and family. I suspect this may be true for many others as well. So I can’t say for sure that my relative slenderness as a young runner and marathoner was only due to the exercise.
Twenty odd years later, running doesn’t do the same thing for me. I have a family—we cook great meals in our house, enjoy desserts, and generally relish living. Is it the inevitable middle-aged spread? Is it due to reductions in hormones related to the aging process? Not exercising enough? Is it due to excess calories in general? Or fat or carbs in particular?
I started using an ankle brace regularly on trail runs (see for example Monte Bello OSP or the Bay to Ridge Trail) about 2 years ago to prevent the perennial ankle sprains I am susceptible to (it has worked well!). I was able to train more or less consistently for longer periods of time. My weight stabilized, but I couldn’t seem to lose any weight, even with ever increasing mileage. An hour or so of jogging or uphill walking most days was typical, with occasional 3–4 hour outings, frequently covering a few thousand feet in elevation change. You’d think the weight would just fall off, but it didn’t. Any interruption in training saw the weight pile on quickly too (whether due to breaks from work demands, bad weather, holidays and holiday eating, illness or injuries). I think there is a tendency after long or hard exercising to believe that you are entitled to a few extra calories, and slightly larger serving sizes of food become habitual, and there goes any weight loss! It’s trivial to eat a few hundred calories extra, and not so trivial to burn them off. (See, for example, the chart at myfit.ca.) Also, there is evidence that exercise increases insulin secretion and growth hormone production (but that’s another post…). Certainly I have found myself famished after longer training events, and not satisfied with just one meal.
So why did it seem to work when I was in my twenties? I’m not sure—there are many factors that could have contributed. More importantly, why is it working now that I’m restricting carbs in my diet? I’m not even sure the exercise has anything to do with it. We’ve seen some of the fastest decreases in weight when exercising the least. For example, after an injury (I dislocated my elbow in early May) and cutting back on distances and speed, I spent a whole month with my weight consistently below the trend line on my weight loss graph. Afterwards, we started doing more distance again and pushing the pace, and the weight actually increased for a few weeks. (See our earlier posting about weight loss curves.)
My experience is, I think, quite typical of active males. I've always been a fast eater with a relatively high metabolism. Fast eaters tend to overeat a bit, and I tended to be 5–10 lbs above my ideal weight as I was growing up. I then went through periods when I was extremely active and periods when I was relatively sedentary. As a competitive varsity athlete in college, the weight naturally came off. It also came off when I spent summers mostly outdoors backpacking a lot and when I worked more physically active jobs organizing trail runs and doing construction work. I also ate more at those times. As I've gotten older, my weight has gradually gone up roughly along the typical pound-per-year curve. There have tended to be spikes when my level of activity decreased suddenly (when I stopped doing the physically demanding sport or job, and I had to relearn how to eat less and feel satisfied). The weight always seemed to have a local (in time) set point that was not very dependent on short-term variations in the amount I ate.
A few years ago, I switched once more from a period of high-activity work to more sedentary work, and my weight started drifting upward alarmingly even with significant efforts at reducing calorie intake. Essentially, I was starting to exhibit the typical set of symptoms known as metabolic syndrome: weight gain, increased waist circumference, moderate elevation of blood glucose levels, moderately elevated triglycerides, high blood pressure. If I paid close attention to my weight and caloric consumption, I could temporarily get some of the weight off, but it tended to come right back as soon as I stopped paying attention or went through a holiday period. Adding back in a strenuous exercise program also helped temporarily, but always tended to drive up my calorie consumption. Basically, I was confirming the usual experience that diet and exercise only sort of/maybe work to keep weight under control, and only if you pay close attention and keep paying attention. I've now lost all of the recent excess weight gain (about 25 pounds), though I'm still 30 pounds over what I weighed as a college athlete. The secret has really been exactly what my pediatrician told me 40 years ago before we all went low-fat, low-cholesterol: cut back on the simple starches and sugars! I don't make any attempt to calorie-restrict, or count calories—I'm rarely unusually hungry. I've just cut way back on the amount of sugars, potatoes, and grains I eat. End of story.
If anything, our relatively generous exercise schedule seems to lead to an ability to tolerate a few more carbs in our diet, but I’m sure if we restricted even more, we’d lose faster. Having adapted to a low carb diet, our metabolisms are acting in a carb-sparing capacity, using fat preferentially so that the glycogen is there for emergencies. It’s unclear whether we are even glycogen-depleted anymore. Certainly our blood glucose levels are stable—the body readily manufactures glucose from protein, and we eat sufficient protein so that we’ve never really been all that ketogenic (we’ve checked).
The body contains something like 400 g glycogen, stored in muscles and the liver. This glycogen binds 2.6 g water per gram of glycogen, and hence the total weighs 1440 g in total in the body—3.2 lb). Low carb critics often incorrectly state that the weight lost on a low carb diet is only “water weight,” due to the loss of glycogen stores. Those 400 g of glycogen theoretically contain about 4 kcal/g of metabolic energy (assuming efficient conversion), so that’s 1600 kcal worth of carbs that could theoretically be eaten each day if you burned all the stored glycogen for energy during exercise.
Of course, that’s not how it actually works in aerobic or mixed aerobic/anaerobic exercise. Unless you are exercising beyond your anaerobic threshold for long periods of time, or your aerobic fitness is very poor, fat is the preferred energy source for exercise. Just keeping to a pace where my heart rate is elevated (130–160 beats per minute) means I must cross the anaerobic threshold at least some of the time, but even so, there’s no way that I deplete all my body glycogen during normal exercise. One exception might have been a time about two weeks into our low carb diet when we went on a particularly difficult route, climbing and descending about 2000 ft and covering about 11 miles (in a cold rainstorm!). By the end, I was cramping and weak (might have been due to the cold too), and my blood glucose was down to 76 mg/dl. Every other time, even if exhausted to the point of feeling ill, my blood glucose was never below 90 mg/dl. I was never in any danger of completely running out of glucose for fuel (or fat!). (See this nice discussion of fat vs. glycogen burning in distance training.)
So if you are eating 2000 kcal at 60% carbs as recommended by many medical professionals, that's 1200 kcal from carbs consumed every day. But it's very unlikely that you will use up and need to replenish that much glycogen every day from normal exercise and living activities. Unfortunately, the body naturally stores at least some of the excess as fat.
So, our conclusion to date is that exercising is a great thing to do, but is not necessary or necessarily even helpful for weight loss at all (though of course it is very helpful for general health, increasing insulin sensitivity, raising HDL levels, etc.) On the other hand, if you eat large amounts of carbs, you'd better burn it off somehow or the likely destination for a lot of the excess is your fat stores!
Saturday, July 26, 2008
Even among those who are supposedly being more discriminating about their food choices, fruits are almost always treated as something to eat in large, if not unlimited, quantity. For example, the Paleo Diet, which attempts to recommend a diet alleged to be similar to that of our hunter-gatherer ancestors, recommends consuming "all the fruit and non-starchy vegetables you can eat." (You are warned against eating too much dried fruit—most fresh fruits are about 80–90% water, so removing most of the water can dramatically increase the total quantity you can eat. Similarly, some people warn against drinking too much fruit juice which is another way you can consume a lot more fruit very quickly.)
Fruits are alleged to be good for you, because they contain a lot of essential vitamins and minerals as well as fiber and such newer necessities as "phytochemicals" and "antioxidants." So what's really in fruit? Even those of us who habitually read nutrition labels tend to be unfamiliar with the nutritional content of most fruits, since, as typically sold fresh, there aren't any nutritional labels. The following table gives some data for a lot of common (and a few less common) fruits.
|Fruit||Protein||Fat||Carb||Fiber||Sugar||Fructose||Glucose||Sucrose||Other||All based on 100 gm serving|
|Apple||0 g||0 g||13 g||1 g||10 g||6 g||3.2 g||0.8 g||7% C|
|Apricot||1||0||11||2||9||0.9||2.4||5.9||39% A, 17% C, 7% Potassium|
|Banana||1||0||23||3||12||4.9||5.0||2.4||15% C, 18% B6, 10% Potassium, 13% Mn|
|Blackberry||1||0||10||5||5||2.4||2.3||0.1||35% C, 32% Mn|
|Blueberry||1||0||14||2||10||5.0||4.9||0.1||16% C, 24% K, 17% Mn|
|Breadfruit||1||0||27||5||11||48% C, 7% Thiamin, 6% Mg, 14% Potassium|
|Cherry (sour)||1||0||12||2||8||3.5||4.2||0.8||26% A, 17% C|
|Cherry (sweet)||1||0||16||2||13||5.4||6.6||0.2||12% C, 6% Potassium|
|Cranberry||0||0||12||5||4||0.6||3.3||0.1||22% C, 6% E, 6% K, 18% Mn|
|Date||2||0||75||7||66||32.0||33.7||0.5||8% Niacin, 12% B6, 8% Pantothenic Acid, 6% Ca, 14% Mg, 6% P, 20% Potassium, 18% Cu, 15% Mn|
|Fig||1||0||19||3||16||6% K, 6% B6, 7% Potassium, 6% Mn|
|Grapefruit (pink)||1||0||11||2||7||1.8||1.6||3.5||23% A, 52% C|
|Grape (red or green)||1||0||18||1||15||8.1||7.2||0.2||18% C, 18% K, 5% Potassium, 6% Cu|
|Guava||3||1||14||5||9||12% A, 381% C, 6% B6 12% Folate, 12% Potassium, 11% Cu, 8% Mn|
|Kiwi||1||1||15||3||9||4.4||4.1||0.2||155% C, 7% E, 50% K, 6% Folate, 9% Potassium, 6% Cu|
|Mango||1||0||17||2||15||15% A, 46% C, 6% E, 7% B6|
|Melon (honeydew)||1||0||9||1||9||3.0||2.7||2.5||30% C, 7% Potassium|
|Nectarine||2||0||15||2||11||1.4||1.6||4.9||7% A, 9% C, 6% Niacin, 6% Potassium|
|Orange||1||0||12||2||9||75% C, 7 Thiamin|
|Papaya||1||0||10||2||6||22% A, 103% C, 10% Folate, 7% Potassium|
|Passion fruit||2||1||23||10||11||25% A, 50% C, 8% Riboflavin, 7% Niacin, 9% Fe, 7% Mg, 7% P, 10% Potassium|
|Peach||1||0||10||1||8||1.5||2.0||4.8||7% A, 11% C|
|Pear||0||0||15||3||10||6.2||2.8||0.8||7% C, 6% K|
|Pineapple (sweet)||1||0||13||1||10||2.2||1.7||6.5||94% C, 6% B6, 6% Cu, 41% Mn|
|Plum||1||0||11||1||10||3.1||5.1||1.6||7% A, 16%, C|
|Pomegranate||1||0||17||1||17||10% C, 6% K, 6% Pantothenic Acid, 7% Potassium|
|Raspberry||1||1||12||6||4||2.4||1.9||0.2||44% C, 10% K, 34% Mn|
|Rhubarb||1||0||5||2||1||13% C, 37% K, 9% Ca, 8% Potassium, 10% Mn|
|Strawberry||1||0||8||2||5||2.4||2.0||0.5||98% C, 6% Folate, 19% Mn|
|Tamarind||3||1||63||5||57||6% C, 29% Thiamine, 10% Niacin, 7% Ca, 16% Fe, 23% Mg, 11% P, 18% Potassium|
|Watermelon||1||0||8||0||6||3.4||1.6||0.1||11% A, 13% C|
(All data from nutritiondata.com. Vitamin and mineral content are given as % daily value. 'K' is Vitamin K; potassium is spelled out.)
As you can see, fruits are mostly sugar and water. There's typically about 1% protein, no fat, a modest amount of fiber, and a very small amount of more complex nutritive carbohydrate. Some fruits are admittedly good sources of particular vitamins and minerals, but you get a pretty generous "spoonful of sugar" with your daily dose of vitamins and minerals if you get them mostly from fruit. If you're after the trace nutrients, you'd be better off with vegetable sources anyway. Compare the following (the first three of which are arguably "fruits" in the botanical sense, although we usually call them "vegetables," because of the ways we tend to serve them).
|Tomato||1||0||4||1||3||1.4||1.2||0.0||17% A, 21% C, 10% K, 7% Potassium, 6% Mn|
|Green Bean||2||0||7||3||1||14% A, 27% C, 18% K, 6% Thiamine, 6% Riboflavin, 9% Folate, 6% Fe, 6% Mg, 6% Potassium, 11% Mn|
|Broccoli||3||0||6||2||2||0.7||0.5||0.1||12% A, 149% C, 127% K, 7% Riboflavin, 9% B6, 16% Folate 6% Pantothenic Acid, 7% P, 9% Potassium, 10% Mn |
There doesn't seem to be any good reason to eat fruits for their higher vitamin content; the vegetables have more vitamins anyway! Vegetables provide generous amounts of fiber as well.
So then maybe fruit sugars are somehow better for you? Certainly many "natural foods" advocates seem to believe that "natural" and "unrefined" sweeteners are somehow OK when table sugar is not. But the sugar in most fruits is nutritionally almost the same as that of table sugar. Table sugar is sucrose which is a disaccharide made up of equal parts fructose and glucose. Most fruits also have approximately equal amounts of fructose and glucose either separately or combined as sucrose. The body breaks apart the sucrose right away. Fructose and glucose are metabolized somewhat differently. While fructose has an apparently lower glycemic response, it appears to be more harmful overall resulting in elevated triglyceride levels and fat storage much more than does glucose. So focusing on apples and pears with their higher fructose content is probably even worse than going for the fruits with more balanced sugar content. A more detailed discussion of the metabolism of fructose and glucose can be found in Basciano et al., "Fructose, Insulin Resistance, and Metabolic Dyslipidemia," Nutr. & Metab., 2005, 2:5.
So my conclusion from all this is that fruits are not health food! They're by no means terrible, especially when consumed in moderation as whole fruit, but as macronutrients, they are primarily bags of flavored sugar water. Particularly if you are trying to cut back on total carbohydrate consumption and on sugar consumption in particular, you should seriously consider limiting your fruit intake and increasing your vegetable intake instead, or at least focusing on lower-sugar fruits such as raspberries, blackberries, and cranberries. For us, fruit is relegated to the role of dessert, to be consumed once or twice a day in ~½-cup portions, to alleviate carb cravings. This way, the sugar loading from fruit is kept to a minimum of 20–25 g.