The “Science” behind “Bonking”

It has long been “common knowledge” that endurance exercise is fuel-limited. This is most familiar to general populations as a commonly observed limitation on foot races that says that you will run out of energy, “hit the wall,” or “bonk” at around 20 miles. For common race distances, the effect is most frequently observed in the marathon (26.2 miles). The standard explanation is that you can only store a limited amount of carbohydrate fuel in the form of muscle and liver glycogen, and that you will bonk when the supplies run out. Management of the “problem” is variously accomplished by “carb-loading” before the race to super-fill (“super-compensate”) the glycogen stores, and by various refueling strategies during the race (which support a large industry that provides special drinks, gels, bars, and the like).

At the same time, there is a growing body of evidence that there is no reason to depend on stored carbohydrate fuel which is limited in quantity if you can mobilize your fat stores as a source of fuel. The problem seems to be that anyone who is accustomed (adapted) to eating a high-carbohydrate diet tends to preferentially burn carbohydrates as fuel and does not utilize the energy available from fat in a way that spares carbohydrate use during endurance exercise. These are the so-called “sugar burners” as compared to “fat burners.”

There are a few possible strategies to enhance fat burning. The most commonly discussed strategy is to train at slower, more aerobic paces, to train the body to optimize using fat as fuel. This approach was discussed by Alan Couzens. Although carbohydrate was also restricted, the main emphasis was on low intensity training, with pretty amazing results from the combined approach.

A second strategy, perhaps even simpler, is to change to a low-carbohydrate diet. Maintaining glycogen supplies in a partially depleted state encourages the development of aerobic apparatus via the action of AMP Kinase (increased mitochondria and associated fat burning enzymes such as carnitine palmitoyltransferase, necessary to help transport fatty acids across the mitochondrial membrane). People with deficiencies of carnitine palmitoyltransferase are unable to utilize fat for fuel efficiently, and can even suffer damaged muscles and rhabdomyelosis resulting in kidney failure. There is also evidence that people suffering from obesity and diabetes may have impaired mitochondrial function, which inhibits their fat burning and at least partially explains the origins of their condition. Similarly, a deficiency of carnitine can result in impaired mitochondrial function and even lead to symptoms of metabolic syndrome.

There is an adaptation period of a few weeks to lowering carbohydrate intake during which the appropriate metabolic pathways and aerobic enzymes and cofactors are up-regulated to better utilize fat as a substrate, allowing blood glucose levels during exercise to be more easily maintained. As Alan Couzens explains, lower carb intake should result in a 20% increase in fat burning in a few weeks. Numerous scientific studies bear this out. A recent study, for example, concludes that a high fat diet increased the rate of whole-body and muscle fat oxidation while reducing the rate of muscle glycogenolysis during submaximal exercise, even after restoring high carbohydrate intake. In this study, a high fat diet was followed for up to two weeks (which we know is just long enough to see significant adaptation), during which usual training was followed. A high carbohydrate diet was restored for the last few days along with a taper before racing. The athletes were able to maintain the increased fat oxidation even after reinstating high carbohydrate intake.

There is at least one supplement (Vespa) which is alleged to improve fat-burning during exercise. There is also some evidence that, all else being equal, the athlete that has the most efficient fat-burning ability can consistently beat the athlete with the higher raw power output (higher VO_{2 max}) in endurance competition.

An article in Running Times last year discussed the strategy of carb cutting to increase endurance, though the article suggests mainly forgoing carb supplementation on training runs, not going low carb in the training diet. The Ethiopian runners again are cited as evidence that a high carb diet is necessary to fuel runs, and there is speculation that they are somehow training themselves not to use glycogen as the predominant fuel by not consuming carbs while actually training. This conclusion seems unlikely to us, since it is well known that exercise causes an increase in blood sugar (due to action of epinephrine and glucagon), effectively mimicking the result of taking in supplemental carbohydrate while exercising. A marathoner does not “hit the wall” until they have run ~20 miles at race pace anyway, a condition not likely encountered during routine training runs for most of us.

Despite all that is known about “the wall,” people persist in believing that a high carbohydrate diet is necessary if you hope to be a good runner. A high carbohydrate diet may work well for Ethiopian runners, who are known for running prodigious mileage and training three times per day. At this training intensity, we seriously doubt their glycogen stores are ever completely full, and they may effectively be training in a perpetually glycogen depleted state, which would upregulate the same enzyme systems that occurs in the low carbohydrate condition. Perhaps what they are mainly training is the rapid replenishment of glycogen stores. However, for most of us amateur or older runners, we’re only fooling ourselves if we think we need to fuel exercise with a high carb diet. David does quite well on very minimal carbs (less than 50 g/day), while Cynthia prefers closer to 100 g/day. Since we generally only run once per day and even then usually less than 10 miles, there is no reason to consume any more carbs to fuel our exercise habits.

David has been a low-carb runner for more than two years now, keeping carbohydrate consumption low before, during, and after endurance exercise. While he won’t brag about his speed and has no plans to challenge any course records, he consistently finds that he has even energy levels and rapid post-event recovery with minimal muscle aches and pains. Fat fueling works for him! However, until very recently, while he refueled less often than is typical, he did routinely refuel using protein and fat for any event of more than 3–4 hours.

He was prompted to revisit the issue when he heard about a recent study (“Metabolic Factors Limiting Performance in Marathon Runners”) by Ben Rapoport when he had his fifteen minutes of fame on NPR in October 2010. Ben was attempting to model bonking in the context of marathon runners. David subsequently exchanged e-mail with Ben whose initial reaction was to interpret David’s personal experience as simply confirming Ben’s model, arguing that fat-fueling works, and that you don’t bonk as long as you run sufficiently slowly. David pointed out some flaws in Ben’s interpretation of the scientific data he analyzed and challenged him to define a performance that David might personally be able to achieve that he might consider sufficient to disprove his model, but he never responded to the challenge. We summarize here both a couple of the criticisms of Ben’s model and analysis and some more recent personal experience and experiments.

A key part of the experimental data that Ben used in building his model came from Romijn AJ, Coyle EF, Sidossis LS, Gastaldelli A, Horowitz JF, et al. (1993) “Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration,” Am J Physiol 265: E380–E391. That paper shows (in Fig. 8) the relative amount of particular substrates which are used in short-term exercise at three different intensities. The subject’s dietary habits were not identified, and any changes that might take place over more than a few minutes were ignored. The data show that more intense efforts use primarily muscle glycogen as fuel. They do not show the pathways that feed the muscle glycogen. Glycogen and glucose are rapidly interconverted, and over longer periods of exercise, new supplies of glucose are made by the liver. The liver, in turn, is capable of using any available fuel source via gluconeogenesis to keep blood glucose levels up. These fuel sources include ingested carbohydrates, protein, and fat as well as lactate, glycerol from liver and adipose tissue fat stores, and even body protein stores such as in muscle tissue. Which source predominates depends on availability. Some of the necessary up- and down-regulation of different metabolic pathways can take place on a short time scale to respond to instantaneous demand for fuel from the muscles and other bodily functions. However, there are also some key adjustments that respond more to average demand and supply to deal with changing diet, exercise demand, starvation, and the like, and these are events that tend to have time constants measured in days or weeks, not minutes or hours. The adaptation processes may be numerous and complex (or at least, we fully admit that we don’t understand all of them) and likely include adaptations in the skeletal muscles as well as in the liver. However, we think it is clear that the data extracted from Romijn do not actually show the underlying consumed fuel source for various levels of endurance exercise, and the data cannot reasonably be extrapolated to model and predict bonking.

One factor which Ben cites in favor of the importance of carbohydrate and fueling is the relative stoichiometry of oxygen consumption for each substrate. He states that carbohydrate oxidation typically generates approximately 120 kcal per mole of respired oxygen, whereas fatty acid oxidation typically generates only approximately 100 kcal per mole of oxygen. We would argue that this, while probably correct, is irrelevant in that the difference is relatively small, and the availability of oxygen is never a limiting factor at a typical aerobic marathon pace. There is always an excess of oxygen available. In any case, regardless of the underlying fuel used to generate blood glucose/glycogen, the immediate muscle activity (except for very short term bursts of power) is fueled by glucose.

Notwithstanding the possible flaws, Ben’s model does make predictions as to whether one is likely to bonk in a marathon. In particular, he has provided a calculator for the marathon. Putting in the best estimates David has for his personal situation, the calculator predicts that he should not bonk for finishing times over about 3 hrs. Since he can only sustain a 3-hour marathon pace for about 1 mile or so, he may never be able to really challenge the model experimentally using himself as a test subject.

However, David was inspired to test his need for refueling during running, and now has a significant number of test results that, if not sufficient to explicitly challenge Ben’s model, are at least startling to many people. For some time now, David routinely runs training runs of up to 4–5 hrs without refueling (water alone). This is still true when he runs with his son at faster speeds who typically chooses to refuel using at least a couple of energy bars or gels. David first pushed the envelope a bit on what was supposed to be a planned 18-mile run that stretched to about 26 miles when the route was blocked by an impassable rain-swollen river crossing. That run extended over about 7 hours including some significant rest breaks, so it was not at a strenuous pace, although it did include some significant elevation change. David consumed only water. The next experience was a 50K (31-mile), mostly flat run, again at a very modest pace, finishing in 6:50, again on water alone. Two weeks later, he completed a much more strenuous 50K on rough rocky trails with about 6000 ft of elevation gain (and loss) in 7:28 on water alone. In all three of these runs, David started with a breakfast of a two-egg cheese omelet and bacon about two hours beforehand. He felt some minor hunger around normal lunch time, but otherwise did not experience any significant fluctuations in energy level, and he certainly did not bonk. His overall weight was down about 3–4 lbs at the end of the day compared to the beginning, but looking at beginning-of-day weights across several days, any weight change was pretty much lost in the noise. Of course, it only takes about a pound of fat to fuel a 50K run, anyway. Another week later David ran yet another moderately hilly 50K event which was slower (8:04) due to snowy trail conditions. Due to a late start (10 am), he chose to eat a little at around the 6-hour mark, mostly because it was a long time since breakfast. However, the ability to do three 50K runs in four weekends, certainly confirms that post-event recovery was rapid.

So what’s the take-away message from all this? It’s interesting to compare our reaction and the experiments that David decided to try to others. Greg Crowther also blogged on Ben’s article. Greg’s big concern was inter- and intra-personal variability, and he questioned the validity of extrapolating from some sort of average measurement of performance to the needs of one individual on one particular day. He didn’t ask (as we did) if too many runners are needlessly afraid of bonking but rather, “if ingesting extra carbohydrates before and during a marathon might help you avoid ‘hitting the wall,’ why wouldn’t you do it? Especially after investing all of that time and effort in training, traveling to the race, etc.?” Hey, we’ll even go further: if ingesting fuel (whether carbohydrate, protein, or fat) during a race might help you maintain a faster pace for whatever reason and for whatever limited portion of the race, even it’s just a placebo effect (or tricking your Central Governor), then by all means go for it! But we also stand by our basic conclusions that (1) carbohydrates are simply not necessary before, during, or after endurance exercise, (2) they’re probably not even particularly beneficial, at least if you are suitably adapted to efficient fat-burning (and may be harmful to your long-term health) and not logging very high miles at high intensity, and (3) unless you’re able and motivated to run, say, an entire marathon at a high percentage of your VO_{2 max}, consuming much of any food immediately before, during, or after the event is entirely optional. Moreover, there may be some benefit to having the stomach completely empty while racing, in order to avoid stomach upset, intestinal discomfort/diarrhea or nausea when running at high intensity. (David does continue to believe in significant protein consumption sometime in the 12 hours or so following strenuous exercise as an aid to muscle repair and recovery, but the timing of even that refueling does not appear to be nearly as critical as some authors suggest.) David will probably resume modest consumption of fat and protein on longer events, just because he’s not big on skipping meals entirely, anyway, but it’s reassuring to know that he can easily keep going without any fuel if for any reason he needs to.

Primal Potatoes—a Contrary View

In a recent blog entry “Primal Potatoes, Part 2” the author tries to make the case that humans are evolutionarily adapted to include starchy foods such as tubers in their diets, and that there would be survival advantage in keeping glycogen stores higher using these sources of starch. We don’t disagree with all of the conclusions he ends up with, but we think that a lot of the “evidence” used is factually incorrect or misleading. Here’s our take:

There is no doubt that the human digestive system has broad adaptability. The fact that humans are “omnivores” who can digest most everything that any animals eat except straight cellulosic materials (grasses and dietary fiber) clearly provides a survival advantage in that it allows humans to survive for at least short periods on whatever food source is available. It does not follow, however, that the ability of humans to digest starches means that they provided a real performance advantage in hunting and/or survival activities and would have been a required part of our diet. Rather, it seems to us that humans are well-adapted to depend predominantly on aerobic exercise (fat-burning) which can be sustained for many hours even in a fasting state if necessary, using the generous fat storage capacity available. Humans have an auxiliary system able to use the much more limited glycogen (carbohydrate) energy stores for primarily short bursts of intense exercise (30 seconds or less at a time) or to supplement for higher intensities than can be sustained by fat burning alone. This auxiliary system is further adapted to replenish/restore itself fairly quickly, again, even without the aid of carbohydrate consumption. While it is possible to create situations in athletic training and competition where the rate of depletion can be faster than can be replenished in steady-state (especially for athletes who normally depend on carbohydrates for much of their calories), it does not follow that such rapid depletion followed by rapid replenishment using dietary carbohydrate sources, was ever important or necessary in evolutionary terms. Note, for example, that athletes in many sports routinely use “reps” or “intervals” of intense activity separated by recovery periods, typically with no consumption of food or drink during the recovery periods. To the extent that fuel stores are being restored during these recovery periods, the process does not depend on any particular external source of calories.

In effect, the body is so effective at conserving and recycling its limited stores of carbohydrate fuels that large dietary replenishment would not have been required to satisfy the needs of hunting and survival activities.

An article by Fournier was cited in “Primal Potatoes, Part 2” to support statements that “whereas typical glycogen stores will support an intense aerobic exercise for a few hours, a single maximal sprint effort will deplete one-third to one-half of glycogen stores,” and “humans can replenish glycogen stores without dietary carbohydrate, and even while fasting.” However, the article link did not work. A PubMed search found this article which appears to match the cited reference. The article describes experiments on rats which were made to engage in moderate exercise (swimming for 30 min with a weight attached to their tails), followed by a 3 min “sprint” (when a much heavier weight was attached to their tails). The main point of the article was to determine if the lactate produced during the sprint was the predominant source of carbon incorporated into newly synthesized glycogen. If you look at Fig. 1, you’ll see that the preceding “moderate” exercise depleted glycogen by at least 50% before the “sprint,” which then further depleted glycogen (down to ~25%). The researchers concluded that the lactate only provided ~50% of the newly synthesized glycogen, which actually is not surprising given that the previous glycogen depleting activity had already reduced the amount of glycogen available, and presumably any lactate that was or could have been produced and therefore recycled into new glycogen had already been oxidized completely and was no longer available. In short, the cited article does not support the first statement, which appears to be an exaggeration. There was no study showing that a single maximal sprint would deplete one third to one half of stored glycogen. Rather, the already ~50% depleted glycogen stores were further depleted by the “sprint,” showing only that the higher intensity the effort, the more rapidly the glycogen was depleted. A “single maximal sprint effort” as we understand it would most certainly not deplete a large fraction of glycogen stores. It may feel like it, but that feeling is not due to glycogen depletion per se, but rather due to acidification due to lactate and carbonic acid accumulation.

There is some confusion as to the meaning of the word “sprint” and how different available fuel sources are used by humans in sprint versus endurance events. True “sprints” (short bursts of maximal effort) do not even depend on glycolysis, which is too slow. There is a third energy storage and release system based on local stores of ATP and phosphocreatine. These are typically sufficient for about 7 sec of peak power output, and are rapidly regenerated during any rest periods using energy from aerobic glycolysis or fat metabolism. (See, for example, Noakes, Lore of Running, p 154.) But even a 100 m sprint by a world-class runner takes longer than 7 sec, and some energy must then come from glycolysis. Perhaps a single clean-and-jerk or other 1 rep maximum weight lift can be completed using primarily this sort of burst of maximal energy, but even a typical set of 10–15 reps in weight training takes longer.

Most people probably think of a “sprint” as something roughly equivalent to a 100 m or maybe as much as a 200 m maximum-speed run. Such efforts typically take about 10–30 sec to complete and, while not possible using only the local ATP and phosphocreatine stores, the effort can be completed mostly anaerobically, fueled by local glycogen stores. The 30-second maximum for this kind of effort is probably limited by the acidification resulting from the rapid production of lactate. What glycogen has been depleted can regenerate rapidly when the maximal effort ends. “Recovery” for a repeat of a similar effort largely consists of clearing enough of the accumulated lactate to relieve the sensation of “burning” in the muscles. Fuel depletion is not a major issue.

Three minutes of a “sprint swim” (or an 800 m run or a flight from a predator) is a much more complex sort of “maximal effort.” It is not a sprint as usually defined for humans. It is a “middle distance” that cannot be completed purely anaerobically. Even an 800 m run (2 min of effort for good runners) is considered an endurance event (requiring stamina), and much of the speed can be developed using aerobic training, though a maximal effort of this length will utilize primarily glycolysis and generate a lot of lactate temporarily. (See http://www.lydiardfoundation.org/news/pdfs/Snellcourirenglish.pdf.)

Clearly the maximum power output that can be maintained for a few seconds cannot be maintained even for 30 sec. A several minute effort is still in the range where a human is capable of power output that exceeds levels that can be sustained for much longer periods of time. The relative contributions of the available metabolic paths to energy generation for an maximal effort of a few minutes can vary widely depending on the individual, the level of normal activity, training or conditioning, dietary habits and adaptations, and the level of actual effort relative to the individual’s maximum capabilities over that distance or time. Anaerobic metabolism of glucose from glycogen is certainly one of the possible contributors. In fact, the limit to how fast any one individual can go for, say 3 min of “maximal effort” is probably still set by acidification caused by lactate accumulation (and carbonic acid from CO₂ produced) due to anaerobic glucose metabolism. As the anaerobic metabolism of glucose is very inefficient and would rapidly deplete stores, additional more efficient metabolic pathways will be tapped, most notably aerobic metabolism of fat and glucose. Another important contribution comes from the aerobic metabolism of the lactate (produced from anaerobic metabolism of glucose mentioned above). If lactate is being overproduced, some of its carbon will be further metabolized in the heart and muscles and converted to CO₂ through the citric acid cycle, and eventually breathed out, with most of the potential ATP from the glucose being realized eventually, even if not in the muscle of origin. At modest production rates, much of the lactate can be used aerobically and directly as fuel by the muscles, and is a preferred fuel of slow twitch and heart muscle. In addition to possibly being used by other muscles, this lactate is also taken up by the liver and converted back into glucose and then glycogen, and thus recycled. In short, it takes a lot more than a 3-minute burst of effort to substantially deplete glycogen stores. In fact, calculations show that the glycogen stores of a well-trained runner are sufficient to last for approximately 2 hours if glycogen is the exclusive fuel (and, incidentally, stored fat would last for about 59 hours [estimates based on glycogen and fat stores present in lean elite athletes]).

Thus, it is simply not true that there would be an urgent need to fully replenish severely depleted glycogen stores after a single episode of high-energy activity. The glycogen stores would not be significantly depleted (e.g., >50%); any of several available replenishment mechanisms would be sufficient to provide necessary restoration; and there is, in any case, no urgent need to provide complete restoration within 24 hours anyway.

This renders meaningless all of speculation in the post about the large amount of protein that would need to be consumed to replace the allegedly depleted glycogen. Let’s consider first, how the body actually uses its glycogen stores. Many authors tend to focus on how much total glycogen can be stored in muscles, how much activity that amount will support, and how much time is required to replace and completely refill the muscle glycogen stores. This way of thinking may be relevant when trying to achieve peak athletic performance for a particular competitive event, but this artificial effort would not be relevant to “normal” life and evolutionary pressures. In "normal" life, maximal effort may be required on occasion, but would be punctuated with adequate rest periods to allow recovery and maintenance of energy stores. Glycogen available to any given muscle for short intense effort is only that stored locally in that muscle—you can’t steal from other muscles. Similarly, once stored in the muscles, it remains there until used—it is not depleted beyond a certain level that is protected and maintained even after extensive exercise.

Even after an exhausting race, a person can still increase their efforts and sprint to the finish. A critical detail to remember is that lactate produced from glycolysis can be used to regenerate glucose and then glycogen, as well as enter the citric acid cycle and be used aerobically. Hence lactate is recyclable—glucose can be used anaerobically for a brief intense effort, then rapidly regenerated from lactate once there is a rest period. Under conditions of carbohydrate restriction or partial glycogen depletion, the body simply intensifies the recycling effort and favors use of fat for most energy needs. Only during periods of long and repeated exhaustive glycogen depletion would glycogen levels be dangerously low, and then the body would attempt to reserve them for emergencies, decreasing intensity of activity to levels supported by fat metabolism.

That said, the amount of glycogen storage for any given muscle is also “trainable” in that the amount of glycogen stored increases with increased use. A well-trained athlete may be able to top out his muscle glycogen stores at as much as three to four times that of a sedentary individual. And presumably, a paleolithic hunter is more similar to a modern athlete than to a couch potato. Further, the “normal” steady state condition for an active individual is probably not with glycogen stores full, but more like half full. This seems to be the condition measured for endurance athletes in steady state (i.e., several hours into a many-hour event or in everyday training. See Noakes, Lore of Running pages 101–102 and references therein). It may take a day or more of resting and relatively high carb eating to fully replenish glycogen stores to maximum capacity, but the half-full steady state can be maintained more or less indefinitely, and is fully capable of supporting most any activity that is needed. Further, at least for individuals adapted to fuel their activity primarily on fat, this steady state can be maintained with little or no carbohydrate consumption, and at levels of protein consumption that are modest compared to any levels that might overwhelm the kidneys.

A further point is that it is possible that this “half full” condition is optimal for health, in that muscles that are not topped out with glycogen are still hungry for more glucose, that is, they still express glucose transporters on their surface that are actively scavenging for glucose. This constant glucose uptake by hungry muscles would tend to keep blood glucose levels low, optimize insulin sensitivity and thereby keep insulin levels low, compared to the condition of the over-fed over-carbed SAD consumers. (See http://ajpendo.physiology.org/cgi/reprint/285/4/E729.)

As soon as liver glycogen starts to decrease, gluconeogenesis kicks in, and if adapted to fat burning, gluconeogenesis enzymes may be up-regulated. One can sustain aerobic activity (presumably using glycogen stores in addition to fat stores) for many hours and still have no measurable depletion of blood glucose levels! In fact, we routinely observe the opposite (elevated blood glucose after hours of running). Glycogen stores can thus be regularly replenished (at least partially- enough to call on in emergencies) as needed even during prolonged aerobic exercise, even when fasting, to support the needs of occasional anaerobic activity. As already noted, data indicates that trained athletes can maintain a steady state level of average glycogen stores that are approximately 50% of their maximum capacity. Put another way, during prolonged periods of inactivity, a trained athlete can store ahead approximately twice the “normal” levels of glycogen stores. (Note that even the “normal” levels are about twice those measured in sedentary humans.)

In the example given of hauling a buffalo carcass out of a ravine, this activity may involve some anaerobic activity, but it will necessarily stretch over an extended period of time and be completed primarily using aerobic metabolism. There may be brief bursts of high intensity effort as needed, and there may even be bursts of extreme effort for particular heavy lifting tasks, but on average the task will necessarily be completed with levels of effort that can be sustained over hours not minutes. We suggest that hauling out a buffalo carcass would not necessarily require a lot of glycogen, and even if it did, would not necessitate gorging on potatoes or other carb food to replenish glycogen stores. Perhaps the one situation outside of athletic competition that could force someone to put out maximum effort for as long as possible (and thus seriously deplete glycogen stores) is a fight (or flight) for life. These events presumably don’t occur in close succession, so the primary evolutionary adaptation would be to provide the capacity to sustain the necessary fight or flight long enough to survive the immediate crisis. An ability to fully recharge is not necessary and would not confer much less of a survival advantage.

In fact, it is often argued that the key characteristic of humans that makes them surprisingly competitive in the predator vs. prey world compared to animals that are nominally bigger, stronger, and faster is that humans don’t depend on their peak power output capabilities but instead on their ability to maintain lesser levels of output for very long times (as, for example, in a “persistence” hunt, where they literally outlast and outrun their nominally faster prey).

Other purported advantages of eating tubers cited in “Primal Potatoes, Part 2”:

1. Lower dietary protein/meat requirement, reducing the pressure for success in hunting large animals, and making it possible to feed more people (offspring) with each kill.

This seems to be a common misconception! Eating less carbohydrate means eating more fat, not more protein. And the hunting of large animals provides increased fat relative to smaller animal sources of protein. It is difficult to eat large amounts of protein, and most people find it almost impossible to eat too much protein. It is true, however, that tubers are easier to store for extended periods than meat (and meat fat) which must be more carefully prepared for long term storage, especially in warmer climates. Agriculture does enable more concentrated population centers and was probably a major driving force for the increasing urbanization of the world. However, it is not at all clear that the sort of monoculture version of agriculture that has come to dominate how we feed large populations is a positive step. In fact it is becoming increasingly recognized that we may be destroying the planet faster with mass agriculture than we ever did by overhunting.

2. Less burden on the liver for ammonia detoxification.

This is nonsense. Again, protein consumption tends to be self-limiting at levels well below anything that would present any significant burden to the liver (or kidneys).

3. Easier to avoid protein poisoning while at the same time maintaining greater glycogen stores.

Again nonsense. Protein poisoning is just not a serious risk. And it is not difficult to maintain more than adequate glycogen stores with very low carbohydrate consumption because glycogen stores do not need to be 100% full in order to provide adequate auxilliary anaerobic energy production.

4. Easier to maintain and increase lean mass in response to the stresses of high intensity activity, with a lower dietary protein requirement.

False! As anyone who has seriously tried a low-carbohydrate diet knows, it is much easier to maintain lean body mass without increasing excess fat storage if carbohydrates are minimized in favor of fats. And carbohydrate consumption always causes blood insulin levels to spike, which has a whole series of negative consequences. Arguably, from a public health point of view, the widespread adoption of higher-carbohydrate diets was the single worst event in human history that is the major cause of most of the so-called “diseases of civilization.” Building lean mass (muscle) is usually easier with adequate protein consumption. The key to maintaining it is to (1) make sure that you maintain sufficient nutrition so as not to catabolize too much of your own protein (which the body will do if other fuel sources are limited) and (2) to consume enough protein for muscle building and rebuilding/repair. (See for example http://www.bodybuilding.com/fun/md92.htm and references cited therein, which provides evidence that excessive carbohydrate consumption post-exercise actually inhibits optimal muscle growth and repair.)

5. Reduced pressure to hunt only the fattest animals by use of carbohydrate instead of fat to dilute the protein content of the diet; which greatly enlarges the pool of potential prey, increasing dramatically the amount of energy available for harvest.

Fat is good anyway! You should always be hunting for your fat needs as well as your protein needs. You just don’t need that much total protein. But you do need some protein, and high quality protein (i.e., the so called “essential” amino acids) is hard to get in sufficient quantity from non-animal sources.

In summary, while we certainly believe that humans likely ate tubers and other starchy vegetables (and eventually the New World potato) when they could be found, we see no evidence that that behavior conveyed any sort of evolutionary advantage beyond survival in times of limited food availability.

SF Marathon Part I: SF Marathon Revisited

As a birthday present to myself, I decided to run the SF Marathon again after 27 years. This race has a special place in my heart since it was the first marathon I ever ran (back in 1982!), and because it was such a wonderful experience then. I thought if I really wanted to judge my fitness now, I should try it again so I can compare the then with the now. But first, let’s talk about why it was so wonderful back in 1982.

In July of 1982, I had only been running regularly for about 10 months. I had been a sprinter in high school and early college, and then crewed for Duke and Stanford, all of which are largely strength/fast twitch or strength/endurance sports. I always hated the two mile timed runs we had to do for crew to judge our fitness, just as I had always hated the warm up for sprint practice. But when I went through some big hiccups in my personal life, I coped with the emotional trauma by running long and hard, mostly at the Dish loop at Stanford, which was convenient because I worked as a research assistant there after graduating from college. I also ran some with friends, most of whom were faster than me. One was running the SF marathon, and I went along as an unofficial runner at the last minute. I didn’t know how to train, and hadn’t in fact done much specifically to train. I had obviously done some longer runs- maybe 8-12 miles, and the weekend before the race, I went out for ~18 miles on the roads from Stanford out through Portola Valley and back. That went ok so I decided I was ready to try the distance. But I was certainly not expecting much, and just hoping to finish. My running partner went out fast and I didn’t expect to see him again until the finish. I sauntered along for a few miles at what felt like a very slow pace. After ducking into a restaurant to use their bathroom (no portapotties at this event!), I figured it was time to see what would happen if I sped up, so I slowly increased the effort level and kept on speeding up until I couldn’t anymore. This worked surprisingly well, and before I knew it, I was steadily passing people, including my running partner (reduced to a painful walk by that stage)! I don’t know why it worked so well (this is all relative of course- real speedy people will laugh at my pitiful accomplishment), but I was thrilled to finish in 3:45, and especially to pass the guy who always made me feel so slow. I still have the medal to this day, which they gave me even though I was an unofficial runner.

So on to 2009. I’ve been running pretty regularly, albeit with injuries of one sort or another for the past year. Last summer it was a piriformis problem, and this past winter, it was hip flexor tightness, along with more piriformis and glut medius problems (opposite hip this time), not to mention sore gluts and hamstrings when I finally got other parts working properly. In trail ultras, there can be a fair amount of hiking due to steep hills and rough terrain, and trails are rough enough that speed isn’t really an option (for me anyway), so these injuries were not debilitating. More recently, I’ve managed to get past those particular problems, and train more or less regularly, and work on pace as well. So I thought it might be time for a comparison with those earlier days. Also, after David injured his knee last May (he’s mostly recovered and faster than before it seems!), I did more road running, starting from home running alone and heading up into the hills, or up to the Dish, while still doing trails some of the time. My usual training was pretty slow, with easy efforts at relatively low average heart rates (~130’s- I can be very lazy, but justify this by saying that it is low stress :) ). I threw in some faster tempo runs and Yasso 800’s starting in June to help raise lactate threshold, and these predicted a marathon time of ~4:10. So I felt like my legs and feet were reasonably acclimated to pavement and my conditioning should be good enough to get me through a marathon in a not too disappointing time.

The Expo: I’ve only done trail races since starting to run and/or train (if what I do can be called training) more consistently in the past year. So the Expo was a first for me and I was eager to see what it was all about. There were lots of samples of drinks and snacks to try, and clothes that looked like fun. But all I bought was shoes- there was a $50 per pair bargain booth, and I got my first Mizunos and a pair of Brooks. I don’t have much in the way of road running shoes (I ran the race in a cheap pair of Adidas from Costco!), so I thought this would be a good plan. We’ll have to see how these shoes work out.

On race morning, David dropped me off a few blocks from the start with only minutes to spare from my wave 6 start time of 6:17. The line for the portapotties was so long, I just gave up and headed to the start. This probably explains the unexpected mix of running speeds in the pack- all those faster people who were delayed for half an hour at the start! Our wave began, and I loped along at about a 10 minute pace, hoping things would thin out soon so I could get up a little more speed. That never really happened though. The pack was very thick all the way out and back across the Golden Gate Bridge. People could never really get their stride due to bobbing and weaving between faster and slower people all the way up to about mile 10. I blame this partly on the portapotty situation at the start, but also we really needed more space! Many people were taking walking breaks, which made it hard for those of us trying to keep a consistent pace. I felt great though, light on my feet (unusual!)- nothing like adrenaline and a crowd of happy people running in cool SF fog! Returning across the bridge, I yelled a loud “Go Julianne” to Julianne , the only other person I knew who was running (she was pacing the 4:45 group). When they offered Gu at the aid station, I obliged and had a couple (the caffeine was a good idea for this night person), downing them somewhere between miles 8 and 13. There was more Gu at mile 16, and I took another. All during this time, my heart rate was running about 145. It rose on the hills, but apparently I made up for any increase on the downhills. I felt like I was fading a bit between miles 13 and 16, but soon thereafter (maybe it was the double caffeinated espresso gel!) realized that if I was going to have any hope of a strong second half, I’d better get moving. I pushed into a heart rate zone of 150+ through Golden Gate Park and down toward the Embarcadero again. I kept pushing and pushing, but unfortunately, there were plenty of hills that kept pushing back. Then there were the diversions- it was very disconcerting to arrive at an intersection and have them pull caution tape right in front of you and send you a different way! Presumably, this trick allowed them to keep some traffic moving across the race route. I still felt ok though, except for cramping calves. The cramping got bad enough that I had to stop and walk a few times, or pull over to the curb and stretch out my legs- they were very very stiff! I met an older man during one of my stretching interludes who seemed concerned I might quit (he was 71, so I can still say he was older, right? ). He was wearing a complicated looking knee brace. When I asked him what the brace was for, he explained that he had arthritis and when his Dr. said he couldn’t run anymore, he said that was not an option. He said his knee actually feels better after he runs! He also explained that he runs at a level of effort to keep his heart rate below 130 (must be nice!). We ran together for a bit, then I went on ahead while I could, trying to get mine back up to 150 or so. Of course, the last few miles of a marathon just suck no matter what- everything was stiff and hurting by that point and I could barely climb up and down over curbs! And it was warming up in the now sunny city! But drag into the finish I did, in a sparkling 4:31!

The post-race food was disappointing, and not on par with post-ultra refeedings. There was carbs and more carbs in the form of bananas, snacks and more sugary drinks, but nothing more substantial, not that I saw anyway. They were very eager to replace our glycogen stores the moment we stopped running, but I wasn’t eager to replace my glycogen stores immediately- I planned on taking at least one rest day to recuperate. It’s not like a multi-day event where you need to be diligent about getting fuel stores replenished right away. After a grueling event as long as a marathon, you need protein to start the process of rebuilding and repairing muscles, not empty carbs! See the very interesting posts by Robb Wolf here and here. We left the food behind quickly, as there was really nothing there of any use to me. We found a gyro place instead, where at least there was mix of protein, veggies and carbs. It was hard to leave behind the massage tables though. They were quite tempting! Fortunately, David gives a good massage too, and I enjoyed his generosity very much once we got home.

I also thought it was interesting that they put water or cytomax into tiny little cups, holding usually no more than 2 ounces! After the race, I was very thirsty and drank the entire bottle of water they handed out at the end almost immediately. Do you suppose they were concerned about hyponatremia, and trying to keep people from over-hydrating?

I made no effort to “Carb-load” for the race. I may have eaten slightly more carbs than usual (maybe 150 g vs 100 g?), but nothing dramatic. The night before, we had plenty of protein and veggies, but also some birthday cake (a spectacular nut torte made by my in-laws). I was pretty happy that there was no outright crash into the “wall” and in fact I felt quite strong through the usual “wall” territory. Whether this was because I used a few gels (75 g worth of carbs), ample caffeine, or pacing so that I burned plenty of fat and didn’t prematurely deplete my glycogen stores, I don’t really know. I never used gels (they didn’t exist!) back in the 80’s when I was faster, and barely drank any of the Gatorade they offered at water stops anyway. Marathons just aren’t that long, and with proper training, you shouldn’t need carb supplementation anyway. But that’s not fashionable now either. Still, I try to keep an open mind and test these theories as best I can.

I wore drymax socks, and despite no blisters on the left foot, ended up with 3 on the right! The odd thing is that these blisters were in different places than I’ve ever had them before. I think an important part of blister avoidance is acclimating the feet to both the shoes you’ll be running in and the running conditions. I could have had tougher skin on those parts of my feet if I’d trained more in those particular shoes and with longer runs on those types of roads. Since I put in only a few longer runs on roads at all, and often in different shoes, my feet just weren’t prepared for the particular stresses of that event. You’d think I would know this by now. Well, live and learn, maybe…

Surprisingly, the Garmin says I averaged a heart rate (HR) of 147 for the first half (at a pace of 10:05) and 145 for the second (at 10:20). All the effort to get the HR up didn’t do much to increase speed overall, but perhaps the problem was the cramping and the heat due to the warming city streets. I certainly tried to pick up the pace, but the hills between miles 15 and 21 made sure the effort went largely to making it up and over them, not speediness. I don’t really think I could have gone much faster, except maybe in the earlier miles if there had been less crowding. By the end, I was pretty beat and going on inertia and will power.

I knew going into the event that I would probably be disappointed, and it was not likely I would have another surprisingly fast run. I wondered if maybe I hadn’t trained adequately, since I ran considerably slower than I had hoped. I mean the Yasso 800’s predicted a 4:10 after all! Perhaps they’re not so accurate. On the other hand, where was the muscle soreness? I had none of the usual post-race muscle soreness! Walking up and down stairs was just normal the days after the race. My body acted as if this was just a hard training run, and I went running again after resting only one day! This argues the effort was not all out. Perhaps I’m too used to ultras and doling the energy out more evenly over a longer period of time. Then there is that laziness factor…

All in all, this was a nice event. There were cute signs all along the race course asking questions about SF history (but it would have been nice to see some answers to those questions too). I saw parts of Golden Gate Park that I didn't even know existed before. The music stations were enjoyable too, if spaced a bit far apart. It was just a nice place to run on a foggy morning with 20,000 other like-minded people.

That said, I think trail ultras are a lot easier, at least for me. There is more variability in the terrain, allowing you to use different gaits, paces and muscles depending on what the trails throw at you at any given moment. At my level, I walk some, stretch more and generally don’t get quite as stiff and depleted as in a road marathon. So more trail ultras are in the plans, but possibly another road marathon. I should be able to run one faster, shouldn’t I? (see Part II, coming up)