Dr. Jack Rutherford

Athletes are always looking for a competitive edge in their diet but have to contend with potential negative health consequences, including increased fat storage and increased risk of coronary artery disease.

Higher fat and carbohydrate diets in particular are front and center in the athletic marketplace, but one wonders whether these diets pose additional risk to endurance athletes.

Two interesting studies have examined the effects of high-fat and high-carbohydrate diets on risk factors for heart disease in endurance athletes.

The first study looked at low (16 percent of calories), moderate (30 percent) and high (42 percent) fat diets on body fat, weight, blood pressure, resting heart rate, triglycerides and cholesterol levels.

The participants (12 male and 13 female distance runners who ran at least 35 miles per week) completed four weeks on the low-fat diet and four weeks on the moderate-fat diet. Twelve of the participants agreed to participate in the final phase — a four-week diet high in fat.

The results showed that in these highly trained athletes increasing the daily fat intake from 16 percent to 42 percent of calories had no negative effects on any of the cardiovascular risk factors, fitness levels or the ability to train.

In fact, the low-fat diet seemed to negate some of the positive effects that exercise is presumed to produce. While on the 16-percent-fat diet, participants actually saw their HDL cholesterol (the good stuff) drop, along with an increase in the total cholesterol-to-HDL ratio, suggesting that their heart disease risk may actually be higher while on a low fat diet.

In the second study, researchers examined the effects of a high-fat (52 percent of calories, 30 percent carbohydrate) diet versus a high-carbohydrate (16 percent of calories from fat, 70 percent carbohydrate) diet on body fat, lean body mass, aerobic capacity, and plasma lipids and lipoproteins in 28 trained triathletes over 15 weeks.

The results showed no differences in percent body fat, lean body mass, weight and total body bone density from baseline to week 15.

The higher-carbohydrate group showed higher triglyceride levels and lower HDL cholesterol over the 15 weeks, while the higher-fat group had no change.

Researchers concluded that because endurance athletes log high volumes of long exercise, increasing the percentage of fat in the diet does not cause adverse changes in the lipoprotein profile, body composition or aerobic capacity, suggesting that it may not only be safe but sound to increase fat content.

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