The Myth of The Optimal Diet

There are a lot of different diets out there. There are low-fat diets, low-carb diets, paleo-diets, vegetarian diets and many more. Proponents of each diet believe that theirs is the best diet for everyone. Thus, while there is a lot of disagreement concerning the specific nature of the optimal human diet, there is almost universal agreement that there is an optimal human diet of some kind—a single best way to eat. True, there are proponents of various “individualized” diets, such as the metabolic typing diet, but these individuals still believe that there is a single, optimal diet for each person.

I don’t. While I can’t claim to be the most knowledgeable nutrition expert in the world, I’ve done my research, and if my research has taught me anything it has taught me that the most salient characteristic of human metabolism is its adaptability to widely different diets. The best available science suggests that the majority of people can make drastic changes to the foods they eat without experiencing drastic changes in their health, especially if they exercise. The human body seems to be exceedingly well designed to make due with what’s available. Thus, if what’s available (or preferred) changes, it’s no big deal.

Proponents of each of these diets—high-carb, high-fat, and high-protein—can point to scientific evidence that it is beneficial to endurance athletes. And that’s just my point: Each of these diets can be beneficial to endurance athletes, and most any individual endurance athlete can probably adapt equally well to all of them.

One analysis of the diet of seven elite male Kenyan runners found that they consumed extremely high amounts of carbohydrate—76.5 percent of calories—and very low amounts of fat (13.4 percent of calories) and protein (10.1 percent of calories). If this diet were in any way inadequate for these individuals, they would not have been capable of the world-class running performances they had achieved.

So, if an extremely low-fat diet is good for runners, a high-fat diet must be bad for them, right? Wrong. A number of years ago, researchers from the University of Buffalo studied the effects of different levels of fat intake on runners. Various health parameters of 25 competitive runners were tracked as they first followed their normal diet, then maintain a low-fat (16 percent) diet, then a moderately high-fat (30 percent) diet, and finally a very high-fat (42 percent), each for one month. (Only a dozen of the subjects agreed to do the final phase). The results were interesting. Good cholesterol levels rose along with the amount of fat in the diet. Everything else—body weight, percent body fat, heart rate, blood pressure, serum triglycerides, total cholesterol and bad cholesterol—remained the same.

Another study by the same group found that competitive runners performed better in a running endurance test on a high-fat diet than they did on a low- or moderate-fat diet. Women in this study saw a bigger boost than men.

The effects of a high-protein diet on endurance athletes are more equivocal. Very little research on the effects of high-protein intake on endurance performance has been done. In one short-term study, New Zealand researchers found that cycling time trial performance was significantly impaired after seven days on a high-protein diet. However, these results leave open the possibility that the athletes would have better adapted to the high-protein diet over a longer period of time and recovered their performance.

The high-protein diet in this study was 30 percent of calories, which is three times the minimum daily requirement of 10 percent. The average American gets 18 percent of his calories from protein. In other words, the average American, including the average American runner, is already on a high-protein diet. While increasing protein intake to 30 percent of calories might have a negative effect on endurance performance, it’s also possible that increasing protein intake from the minimum recommended level of 10 percent of calories to the 18 percent level of the typical American might enhance performance.