Peanut butter or pasta?

By Dr. L. Lee Coyne

Peanut butter or pasta? That is the question asked by many endurance performers as they read some of the new sports nutrition research literature. Following decades of athletes subscribing to the gospel of carbohydrate loading, a new paradigm is raising questions.

Is fat the fuel of the future?

Research published by groups in Denmark, Buffalo, New York, Australia and South Africa are all placing a favorable twist to the concept of "fat loading" as a functional option to carbohydrate loading.

The Danish study reported that the running time to exhaustion, on an 80% of Max VO2 task, was similar in both the high fat diet and the high carbohydrate diet groups following 4 weeks of training while on their respective diets. It also showed, through respiratory exchange ratio (RER) measurements, that the high fat group increased their energy expenditure from fat as training progressed - suggesting an adaptation in progress.

The Buffalo, NY studies showed similar results with no negative blood chemistry indicators indicated.

South African studies compared a high fat group to a high carbohydrate diet group on three types of exercise performance. As expected, during short periods of high intensity (anaerobic type) exercise there were no differences. However, when exercised to exhaustion, differences appeared. The high carbohydrate group lasted 50 percent longer on high intensity bicycle exercise tests than the high fat group. At moderate intensity exercise the high fat group cycled 87% longer than the high carbohydrate group. The latter probably represents the recreational marathoner, the ultra marathoner or the Iron Man competitor whereas the former represents the competitive marathoner. (An intuitive observation not a scientific fact.)

As more studies on the subject appear, the investigations are focusing on the how and why does this happen, at what intensities is the information applicable and does the type of fat make a difference. There are also observations centered on the suggestion that a high fat diet triggers the production of aerobic related enzymes in muscle which allows for more aerobic energy to be available. (There is no anaerobic mechanism for fat metabolism.) There is also speculation that fat loading increases the amount of intra-muscular (between the muscle fibers) fat which is more available for metabolism than the subcutaneous fat and that serves to spare muscle glycogen for longer periods.

I have no conclusions to offer yet. Simply stay tuned with an open mind as this subject unfolds. And remember that muscle glycogen depletion is only a limiting factor in endurance events lasting over 1.5 hours at relatively high intensity. I know of ultra marathoners who consumed peanut butter from the jar during a race.

Happy running while you wonder.