Fat and the Endurance Athlete

Thursday, March 26, 2009 | By Matt Fitzgerald
 
 
 
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Fat is the victim of an unfortunate name. It is all too easy to believe that eating fat makes a person fat. Indeed, for many years most diet experts believed that it did, and many do even today despite compelling evidence that eating a fairly high-fat diet is no more likely to cause overweight than eating a high-carbohydrate or high-protein diet. For example, in a 2002 review, entitled “The Influence of Dietary Composition on Energy Intake and Body Weight,” Roberts et al. noted that 1) fat calories as a percentage of total calories in the American diet had fallen over the preceding 20 years while overweight and obesity rates had increased drastically; 2) studies designed to determine whether people eat more calories when they eat more fat have generally concluded that they do so only when the energy-density of foods in not controlled, suggesting that energy-dense foods rather than fat per se are the cause of weight gain; and 3) studies investigating the effects of reduced fat intake on weight loss have shown that reduced fat intake results in very little weight loss when calories are not controlled, suggesting that it is an excess of calories in general rather than of fat in particular that causes weight gain.

The anti-fat doctrine that prevailed for so long in society at large also prevailed in sports. Generations of endurance athletes, in particular, were schooled to aim for a 60-percent carbohydrate, 20-percent protein, 20-percent fat macronutrient breakdown in their diet. That’s a low-fat diet for sure, since the average American gets 34 percent of his or her calories from fat. While the carbohydrate piece of this formula stood on reasonably sure scientific footing (although it has been modified recently into a recommendation that carbohydrate calories as a fraction of total calories should vary with training volume), the fat piece never had any scientific support. In fact, much of the relevant science indicated that more fat was better.

For example, a study from the University of Buffalo found that female runners who got 30 percent of their calories from fat were significantly less likely to get injured than those who ate less fat. It is not likely that the extra fat itself protected the less-often-injured runners, however. Rather, those who ate the least fat probably did not get enough total calories to meet their bodies’ needs.

Another line of research has shown that higher-fat diets increase fat oxidation during prolonged exercise and may thereby increase endurance. Researchers from New Zealand compared the effects of a 14-day high-carbohydrate diet, a 14-day high-fat diet, and an 11.5-day high-fat diet followed by a 2.5-day carbo-loading diet on fat oxidation and performance in a 15-minute cycling test and a 100-km cycling test.  Performance in the 15-minute test was slightly better after the high-carb diet, but not to a statistically significant degree, while performance in the 100-km test was slightly better, but again not to a statistically significant degree, following the high-fat diet.  Fat oxidation was significantly greater during the 100-km test following the high-fat diet.

Other studies have found that high-fat diets reduce performance in shorter time trials by reducing carbohydrate oxidation. However, recent research indicates that endurance athletes can have the best of both worlds by maintaining a habitual higher-fat diet in training and then switching to a high-carbohydrate diet before competition. These studies have shown that the high-fat diet adaptation of increased fat oxidation capacity persists through the carbohydrate loading period, which in turn ensures that carbohydrate oxidation capacity is not compromised in competition. A study from the University of Cape Town, South Africa, found that a 10-day, 65-percent fat diet followed by a three-day, 70-percent carbohydrate diet increased performance by 4.5 percent in a 20 km cycling time trial preceded by a glycogen depletion ride.

It also bears noting on this topic that the typical endurance athlete gets 30 to 35 percent of his or her daily calories from fat—substantially more than the minimum.  Indeed, even most elite American endurance athletes maintain relatively high-fat diets.  The fact that our most gifted runners, cyclists, rowers, etcetera are routinely able to win national championships on a high-fat diet is the best possible proof that a high-fat diet is not inimical to endurance performance.

Based perhaps in part on this commonsense consideration, as well as on the relevant science, the American Dietetic Association and the American College of Sports Medicine now recommend that athletes get 20 to 35 percent of their calories from fat. Gone is the notion that the minimal adequate level of fat intake is also the optimal or even the maximum acceptable level of fat intake.  It is now recognized that many athletes can perform equally well at a range of fat intake levels, and that some individual athletes may need to experiment before they find their personal “sweet spot” within that range.

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