The depletion or reduction of bodily carbohydrate reserves is associated with fatigue during endurance exercise. Various carbohydrate supplementation and exercise regimens have been used experimentally to increase carbohydrate reserves before exercise or to maintain the availability of carbohydrate for oxidation during exercise. On the other hand, the improved endurance capability observed after aerobic training has been attributed to an increased oxidation of fat relative to carbohydrate; this carbohydrate sparing presumably delays the point at which reduced carbohydrate reserves cause fatigue. This effect has led to the suggestion that a greater availability of fat during exercise can improve performance via the carbohydrate-sparing effect of “fat loading.” Although this is a plausible hypothesis, it is not supported by a sufficient number of valid, credible, and replicated studies. Thus, it appears prudent to advise endurance athletes to consume a diet that is largely carbohydrate to optimize training and competitive performance and, more importantly, to promote optimal health.
W. Michael Sherman and Nicole Leenders are with the Exercise Physiology Section, School of Health, Physical Education and Recreation, The Ohio State University, 337 W. 17th Ave., Columbus. OH 43210.