High fat diet doesn't harm runners' health

The study, thought to be the first to show this effect in women, has important implications for anyone who puts in high running mileage for health purposes. It shows they may be blunting the benefits of running by eating a diet too low in fat.

Previous results from the same study group of athletes showed that increasing dietary fat also improves endurance performance.

The new results, reported in the January issue of Medicine and Science in Sports and Exercise, show that trained male and female runners who consumed a diet composed of as much as 42 percent fat had higher levels of high-density lipoproteins (HDL) in their blood than when on a diet of only 16 percent fat. HDL is the form of cholesterol known to lower the risk of coronary heart disease. LDL, or low-density lipoproteins, is known as the "bad cholesterol" because it has the opposite effect.

The runners, who trained at least 35 miles a week, did not gain weight on the high-fat diet or show an increase in any risk factors for coronary heart disease.

"Liberalizing the fat content gives athletes more calories, and it certainly doesn't harm their health, like everyone thought," said John Leddy, associate director of the UB Sports Medicine Institute and primary author of the study. "We thought the cholesterol ratio would get worse, but LDL and total cholesterol didn't change, and HDL went up. The best thing happened that could have happened.

"I think these results are particularly important for female athletes," added Leddy, research assistant professor of physiology and clinical assistant professor of orthopedics.

"Gymnasts, runners and swimmers, for example, tend to be very concerned about weight gain. Female athletes who consume too few calories to support the energy they expend are at risk for the potentially lethal triad of eating disorders, secondary amenorrhea and osteoporosis."

It isn't the fat, per se, that keeps these athletes healthy, Leddy said, it's eating enough food to supply the body with as many calories as they expend in training, a nearly impossible feat without including foods high in fat.

"This study shows that if they are burning up the calories, it doesn't matter where the calories come from, and it appears that a very-low fat diet is clearly detrimental."

The study involved 25 competitive runners who trained at least 35 miles a week. They spent a month on their normal diets, followed by a month each on diets composed of 16 percent and 30 percent fat. Six males and six females spent an additional month on a 42-percent-fat diet. Protein remained stable at 15 percent and carbohydrates made up the difference in the diets.

Researchers measured resting heart rate and blood pressure, as well as total cholesterol, HDL and LDL cholesterol, triglycerides and the major protein components of HDL and LDL.

Results showed that HDL levels rose as the amount of fat in the diets increased. There was no change in weight, percent of body fat, heart rate, blood pressure, serum triglycerides, total cholesterol or LDL. The 42-percent-fat diet decreased risk factors for heart disease, while the 16-percent-fat diet increased the risk factors for coronary heart disease by lowering the levels of HDL and the major protein component of HDL.

Leddy said the mechanism causing this effect is still in question, but he suggested it may involve the activity of the enzyme lipoprotein lipase.

"Trained athletes have higher levels of this enzyme, which breaks down dietary fat and, in the process, removes plasma triglycerides and forms HDL. If dietary fat is restricted, liproprotein lipase activity is inhibited.

"Also, dietary fat increases the production of the major HDL protein, so dietary fat restriction would mean less HDL protein is formed. Both mechanisms could reduce the beneficial effect training has on HDL levels." An increase in triglycerides raises heart disease risk, while an increase in HDL lowers the risk.

"Runners who restrict dietary fat may inhibit the enzyme and may make less HDL protein, therefore HDL levels may remain blunted," Leddy said.

Also contributing to the study were Peter Horvath, UB assistant professor of nutrition and physiology; Jill Rowland, graduate student in nutrition, and David Pendergast, professor of physiology. The work was supported by a grant from Mars, Inc.