Burke, L. M., & Hawley, J. A. (2002). Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. Medicine and Science in Sports and Exercise, 34, 1492-1498.

"In summary, the results from a number of studies show, that 1-3 d of exposure to a high-fat, low-CHO diet is associated with a lowering of resting muscle (and presumably liver) glycogen stores and a reduction in exercise performance. The impairment in exercise capacity is likely to result from a coordination of the premature depletion of (lowered) muscle glycogen stores and the absence of any worthwhile increase in the capacity for fat utilization during exercise to compensate for the reduction in available CHO fuel. Longer periods of adherence to a high-fat diet, however, substantially enhance the capacity for fat oxidation during submaximal exercise, with evidence that the major shifts in the pattern of substrate metabolism (from CHO to fat) can be achieved within 5-6 d. This scenario presents a practical opportunity for enhancement of endurance and/or ultra-endurance performance via dietary manipulation. Studies in well-trained individuals show that fat-adaptation strategies alone do not enhance the performance of prolonged exercise However, because elevated rates of fat oxidation resulting from high-fat diets are maintained even in the face of acute strategies to promote CHO availability, there is an opportunity to simultaneously enhance the potential for fat and CHO utilization during exercise (i.e., dietary periodization). True glycogen sparing has beep demonstrated after fat-adaptation/CHO restoration protocols during prolonged, submaximal cycling exercise. Nevertheless, despite significant glycogen sparing, studies to date have failed to find clear evidence of benefits to the performance of endurance and ultra-endurance exercise following fat-adaptation." (p. 1497).

It is possible that some individuals are "responders" and others are "nonresponders" to dietary fat-adaptation strategies.

Implication. High-fat diets do not produce consistent effects on endurance performance. At present, the employment of such diets should be on an individual basis after careful assessment of the effect on the individual

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