Unfortunately, these athletes should be concentrating on carbohydrate, not fat, since recent research shows that higher fat intakes are actually associated with reduced gains in endurance during strenuous training.

At the August Krogh Institute at the University of Copenhagen, 10 male subjects trained on exercise cycles for seven weeks while consuming a high-fat diet (63 per cent of calories from fat, 20 per cent from carbohydrate, and 17 per cent from protein), while 10 other individuals trained in a similar manner while ingesting high-carbohydrate fare (65-per cent carbohydrate, 18-per cent fat, and 17-per cent protein). At the end of the seven-week period, all 20 athletes attempted to pedal as long as possible at an intensity of 76% V02max (about 85 per cent of maximal heart rate).

Although V02max rose by 11 per cent in both groups after the seven-week training period, high-carb group members improved their endurance time by 191 per cent (!), while high-fat athletes upgraded performance by only' 86 percent.

Why the big difference in performance? High-carbohydrate athletes swelled their muscle-glycogen levels from 432 to 611 mmol/kg d.w. during the seven-week training cycle, while the fat-eating athletes' glycogen levels didn't budge upward at all. Glycogen is the key fuel which powers competitive endurance performance; as muscle glycogen levels dip, athletes slow down - or stop exercising completely, as the high-fat athletes did.

The high-fat diet also led to additional stress on the athletes' cardiovascular systems. During the test ride at 85 per cent of max heart rate, high-fat athletes' heart rates averaged 174 beats per minute, but high-carb cyclists' pulse rates settled at a much more comfortable 159. Blood levels of norepinephrine - a hormone which can boost heart rate - were considerably higher in the high-fat athletes.

After the seven-week period was over, all subjects engaged in one more week of training, with the previous fat-feasters switching over to heavy carbohydrate consumption and the carbo-eaters continuing to feed on their high-carbohydrate fare. The switch to carbohydrate helped the fat-eaters fill their muscle-glycogen stores, an effect which increased their endurance time by an additional 17 per cent. However, the original fat eaters still couldn't catch up with the high-carbohydrate cyclists, and their heart rates continued to be elevated during exercise.

The lessons? As the Danish scientists pointed out, endurance training combined with a high-fat diet produces hikes in cardiovascular stress, dips in muscle-glycogen levels, and below-normal improvements in endurance capacity - even when muscle-glycogen concentrations are restored. During strenuous endurance training, a high-carbohydrate diet which includes at least 16 calories of carbohydrate per pound of body weight per day is the optimal eating plan

The Danish research doesn't suggest that a nutritional strategy previously discussed in PEAK PERFORMANCE (August 1994, p. 8) - consuming a high-fat diet for eight to 10 days and then switching to carbohydrates for three days just prior to prolonged endurance exercise - should now be thrown out. This strategy may still be viable in certain competitive situations, since the fat binge is confined to a shorter period, and thus should have less effect on the overall training process. Specifically, the 10 days of fat and three days of carbohydrate' plan might work just before a competition lasting for MORE THAN three hours, because such an effort often calls for increased rates of fat utilization.

('Fat Diet Attenuates Training-lnduced Improvement in Endurance but Not in Maximal Oxygen Uptake,' Medicine and Science in Sports and Exercise, vol. 26(5), Supplement, p. 587, 1994)