Why We Run: A Natural History - Bernd Heinrich (2002)
Chapter 17. Racing Fuel
What does not destroy me, makes me strong.
Robins, warblers, and most other songbirds live on an almost exclusively protein diet of worms and insects when they are young and in the nest. That is, they eat meat. Later, when they are mature and get ready for migration, they switch their diet. They require calories for energy, and they then fatten on berries and other carbohydrate-rich foods. Similarly, on their migratory stopovers, birds recoup what they have lost on a previous flight. Birds freshly arrived at stopover points at first gain weight relatively slowly, and they then require a high protein diet to speed up the regeneration of their digestive tract, before they can again feed quickly and lay up fat. Days before departing, while their heart and wing muscle mass is still increasing, their liver, digestive tract, and leg muscles are already becoming lighter, with mass being converted to fat. The birds act as if they optimize organ size for the risks and rewards of fueling and flight. In short, when they are being made, they require raw materials like those that their bodies are made of. Later, they are more like machines that require fuel and much smaller amounts of protein. Similarly, in training for running 100 kilometers, I presumed I’d experience wear and tear that would necessitate resynthesis of tissues. The best foods I needed for long-term maintenance to repair the wear and tear on my body from heavy training would also be protein, but protein would not be the best source of nourishment for short-term fuel in any one race. There are three reasons why I would not consider eating large amounts of protein on a run: the work required to digest it; the poisonous by-product, urea; and the loss of water that would have to be expended to flush the urea out.
Allocating specific foods for training and for racing is not an issue to runners of shorter distances, but as I will show, it was a great concern to me as an ultradistance runner. A sprinter relies almost exclusively on ATP (adenosine triphosphate) and CP (creatine phosphate), the cellular energy currency for immediate, or instant, use. He may also dip into glycogen reserves in the muscles themselves. A middle-distance runner will have to use the glycogen reserves stored in the liver, and access them via the blood to replenish the ATP and CP. Glycogen is an energy-storage molecule the body makes from almost any food containing protein, fat, or carbohydrates, and we always keep a store of it on hand. As far as short-and middle-distance running fuel is concerned, it therefore makes little difference what is eaten, because all food intake gets converted to the same currency of ATP and glycogen. The current 1,500-meter world record holder, who I predict will win the next Olympic gold in that event, is Moroccan Hicham Guerrouj,* who runs on couscous, a carbohydrate-rich food. Finland’s Lasse Viren, four-time Olympic gold medalist, winning both 5,000 and 10,000 meters in 1972 and 1976, attributed his spectacular racing success to a diet of reindeer milk (although I’ll wager his success is more likely due to generous doses of sisu, a Finnish entity that translates roughly to guts and stubbornness).
Problems of racing fuel arise in long-distance running because ATP stores are used up in seconds, and the amount of glycogen the body can store is about 2,000 kilocalories, whereas to run 100 kilometers requires a total expenditure of near 6,000 kilocalories. In most of us, maximum glycogen stores are exhausted even before running to near the marathon distance of 26 miles. Glycogen depletion is described as “hitting the wall” because that is what it feels like when blood glucose (derived from the liver glycogen stores) suddenly plummets. A metabolic switch-over occurs. It is not sudden or absolute, but it occurs. We start to use up body fat and protein as running fuels, or we may refuel by eating on the run. Both of these options greatly compromise speed.
I didn’t know what food would be best for me on an ultramarathon, but I let data from animals point to possibilities. In bees, for example, flight endurance (given no temperature limitation) is almost strictly a function of how much carbohydrate fuel they have in the stomach, and usually that is sufficient to get them where they need to go. A bumblebee with a honey crop full to equal body weight of concentrated nectar (30 percent sugar, 70 percent water) should have a maximum flying time of almost 3 hours. Migrating birds mobilize body fat as fuel. If a bird doubles body weight by laying on fat (but without water), it can fly nonstop for three days and nights. Thus in terms of fuel economy for long-distance travel, fat is much better aviation fuel than a watery sugar solution.
Carbohydrate is better for speed. As long as a bee’s honey crop is not empty, its blood sugar remains high and normal flight speed is maintained. As soon as its crop is empty, flight stops. Similarly, when our blood glucose levels dip, we become weak. The difference is that although we may be too weak to run, we can still walk. That’s because we then dip into the fat and protein reserves that our bodies save for emergencies. Although these fuels contain much energy, it is difficult for us to access them rapidly, as birds can and do. Individual bumblebees and honeybees can afford to run almost totally on carbohydrate because they don’t usually run out of fuel. They always have access to honey stores in the hive of which they are a part. They revisit the hive usually at intervals of half an hour or less. As a consequence, they have not evolved the need to store body fat when they are confronted with a surplus of food—they store extra calories in the hive’s larder instead.
Bee with full honey crop
The whole idea of my trying to increase the fat mobilization into the blood and the fat-burning metabolism of the cells was to delay exhaustion by conserving the precious carbohydrate fuel. Blood sugar (or liver glycogen, and also protein, from which sugar is derived) is absolutely essential for brain function, and one solution to keep glucose levels up on ultramarathon runs is to get carbohydrate from the digestive tract. For most runners, however, the stomach doesn’t cooperate well with running. It seems as if food processing and running are mutually exclusive, and many runners who try to eat and run end up throwing up. That may be an adaptive response for running fast over a short distance. Stomach contents add weight and rob precious blood supply from the muscles, making one feel and be weak. Normally the predator eats after the chase, not before it, and the stomach’s response makes sense. But what if the stomach is trained? I trained by eating a sandwich, a hamburger and potatoes, or even a full meal immediately before a long run. It seldom caused problems, but then I didn’t run fast, either.
Naoko Takahashi, a famous women’s marathon runner from Japan,* claims that the secret of her success is drinking the stomach secretions of the larval grubs of the giant killer hornets, Mandarina japonica, both during training and the race itself. That juice originates from the chewed-up, digested insect prey (mostly bees) the adults catch and feed their grubs in the communal nests. In return for being fed, the 4,000 or so grubs per nest regurgitate clear liquid droplets to these adults, who then fly up to 60 miles per day at up to 20 miles per hour in their hunting excursions. It was this clear liquid regurgitate that Tokyo investigators tested on mice and students, claiming it boosted their ability for fat metabolism while reducing muscle fatigue and slowing lactic acid build-up. (The question is, as opposed to what?) My Maine buddies from the Rowdies Running Club would undoubtedly claim that defizzed Coke or beer is handier, and maybe better. I suspect that the wasp juice contains a very high sugar content and many amino acids (but not more than in honey and meat). As to the wasps’ speed and endurance, bees do even better, and they burn more honey.
I have not yet experimented with wasp regurgitate, but I did try honey, a bee regurgitate. My experiment with honey on the run was when I lived in Walnut Creek, California, and was training for the San Francisco marathon. My long training run took me up into the foothills of Mount Diablo and back, in usually scorching weather. I love honey, but nearly a quart all at once was a push. Nevertheless, I forced it down and headed out the door, running through the suburban sprawl and off toward the mountain. I soon had mixed sensations, but those in the gut predominated. Almost irresistible urges. It was only with great effort that I made the cover of some bushes near the foot of the mountain. Well, I’d made it halfway, but I felt decidedly woozy. I then lost a good deal of liquid along with all the honey, and I think I subjected my body to dehydration among a few other sins. But I learned my lesson well. Until I tried an equal volume of olive oil.
My third experiment was with a combination of lots of carbohydrate and lots of water—beer. I had done my trial runs on a 20-mile course, making a beer cache 10 miles out under some bushes. I timed myself out to the beer, downed the twelve-ounce bottle, then ran on and timed myself with the stopwatch over the second part of the course. If I slowed down, I figured I’d better try something else. If I speeded up, I could be onto something. I had speeded up slightly.
For a real test, I entered a long road race toting three six-packs. Presuming a fast racing pace, I planned on having one every 4 miles. We took off like a rhinoceros in rut, and I was soon in the lead, chugging one beer after the other and increasing my lead even further. While starting to congratulate myself on the great run, with just three beers left to go, I suddenly felt weak. With two left to go, I lost all my will and just dropped out. I felt sick. More fine-tuning would not have been a bad thing if I’d really planned on this as something serious. However, I did not repeat the beer experiments. Instead I tried Ocean Spray cranberry juice. At first, I drank it only after my training runs to counter my usual loss of 4 to 6 pounds of fluids. I never carried groceries with me, because I didn’t like the burden affecting my stride, which I needed to cultivate. I cached the juice along my training route so I wouldn’t have to wait till the finish.
Cranberry juice is, like nectar or dilute honey, mainly a sugar solution. Why not use something more concentrated, like a candy bar or a sandwich? I tried those, too. They were great, unless I was running fast or had already run far and was getting dehydrated, which was precisely when I most needed calories. My mouth would feel as if it were stuffed with cotton, and I couldn’t swallow. I can down six saltine crackers in under a minute (having done so on a bet), but during race conditions, the only way I could ingest sufficient carbohydrate was in liquid form.
Cranberry juice became both my racing fuel and my water. I decided I might as well ask Ocean Spray to sponsor my run by giving me free juice for the race in Chicago. To my delight, they not only agreed, they also picked up the tab for my airfare and hotel reservations. That’s the full extent of material compensation I’ve ever received as an athlete, and it’s all I ever asked for.
I know of nobody else who has tried cranberry juice since. For current advice on diet for an ultramarathon, I quote Jan Vandendriesche of Belgium, on winning Boston’s 100-kilometer challenge on October 10, 1999: “Go light, but stay ahead of the calories. Don’t stuff yourself till you barf. Avoid ibuprofen if possible. Carbofuel for the first half. Start taking GU (a commercial concoction) at about 40 km. Drink Metobol (also a commercial concoction) midway, then nothing except GU, water, and Pepsi (ditto) the last twenty miles.”
A quick perusal of some of the products advertised in Ultrarunning magazine yields Hammer Gel and E-Caps Sustained Energy. Both contain complex carbohydrates plus four “key amino acids,” or protein, and both are advertised as containing “NO sugar.” Then there are Pre-Race CAPS that have electrolytes found in blood plasma, and Recovery CAPS with “special nutrients and antioxidants” for after the race. All of this could be a far cry from eating yeast rolls prior to the race, drinking an almost pure corn-syrup sugar solution with a strong diuretic in it, and looking forward to gorging on steak, baked potato, and apple pie topped with generous servings of ice cream immediately afterward.