Why We Run: A Natural History - Bernd Heinrich (2002)

Chapter 16. Diet

Eating is controlled by psychological drives, which in turn are influenced by blood chemistry. Just thinking about a hamburger can change your blood chemistry. A dog might actually have to see or smell the hamburger first, or at least hear a dinner bell. We can think of the effects on our bodies years ahead, and hence can influence them. Dieting alone has little effect on our brain’s apparently quite strict hypothalamic body weight set point unless combined with strong will. Can the mind affect the set point? If anorexia is any indication, then our minds are indeed powerful enough to alter our hypothalamic set point. So, like an anorexic, I continually visualized thinness.

Our hypothalamus is well known to have control centers that regulate our basic requirements, including the optimum intake of calories, specific vitamins, and other nutrients. We can become dangerously overweight when the nutrients we need are in short supply in the food we eat so that we just eat more, becoming saddled with surplus calories.

In preparing myself for the 100-kilometer race, I would need many nutrients in varying amounts, and I did not presume to be able to figure out which they all were and how much of each I needed. There are no absolutes anyway. Much would depend on conditions. Nutritional requirements when running 20 miles a day in training would presumably be different from those of a normally active person. I could not figure out what I needed, but I was confident that my body would know, in the same way that any other wild animal’s body knows. For example, a pronghorn antelope has a perfect running physique. It eats the right kinds of vegetation without knowing anything about diet. It simply obeys its hungers and aversions, selecting food from the diverse menu it encounters in its environment. I decided to be like such an animal. My body would choose the right things in the right amounts, provided it had the choice of a varied menu of unprocessed or minimally processed food.

There were three additions to my eat-anything-I-want dieting strategy. First, I ran a lot, thus my caloric balance was heavily biased to expenditure. Second, I visualized thinness in the same way that I visualized speed and endurance. The mental visualization itself would not affect my build directly, but it might bias my food intake and training, and thus indirectly affect the ultimate outcome. Lastly, and perhaps most important, I capitalized on my knowledge that I’m a descendant of hunting apes who probably ate meat regularly.

The nutrients that our bodies can’t synthesize must come from our diet. Thus rats, who can synthesize ascorbic acid (vitamin C), have no need for it in their diet. We do need it in our diet, probably because our ancestors ate ascorbic-acid-laden food routinely enough so that there was no need to develop the synthetic pathways to make that substance.

Meat is, to us, much more than a source of calories. It contains all of the amino acids we need to build body proteins. It also contains fats essential for brain growth during childhood, iron needed for oxygen transport, the B vitamins necessary for oxidative metabolism, and vitamins A, D, E, and K. If meat contains all that an animal is, does it not also contain all that we need—aside from the calories burned off in exercise? This is not to say that we absolutely need meat. We can also get the same nutrients from vegetable sources or pills, but proper eating then takes much greater effort. Each animal has its own unique evolved diet. It is easy to overlook some detail when you’re trying to play God. I would rely on my appetite. And the more I ran, the more I craved greasy pork chops.

Judging from later research on migratory birds, it might not have been a bad choice. Fat metabolism is biochemically coupled with protein metabolism, which is why we can’t subsist solely on a pure fat diet but require protein at the same time. Migrating birds get their protein by literally consuming some of the structure of their bodies. Additionally, their and our brains use glucose and not fat for fuel, and after glycogen reserves are exhausted that glucose comes from protein degradation and hence muscle degeneration. For example, the great knot, Calidris tenuirostris, after flying nonstop for 5,400 kilometers between Australia and China shows weight losses of skin, salt glands, pectoral (wing) muscles, heart, liver, intestine, kidneys, spleen, and leg muscle, aside from the huge fat losses. Fasting produces similar results of body protein depletion, and I would rather get my protein out of my stomach than off my muscles and vital organs. In migrating birds and during long fasting, only brain weight remains constant, showing what is really most important and irreducible, in running and in life.