BUFFALO, N. Y. While it is generally accepted that moderate exercise and a low-fat diet are a healthy combination that can help the body fight off infections, a recent study indicates that too much of a good thing may actually produce the opposite result.
The first study to investigate the combined effect of diet and exercise on immune function has shown that competitive long-distance marathon runners who adhere to a very low-fat diet in hopes of improving performance may actually be compromising their ability to fight infection. And, according to the study's lead researcher, the impact on the immune system may even be more severe when the athletes are teenagers.
The study, conducted by researchers from the State University of New York at Buffalo, showed that white-blood cells (WBCs) collected after maximum exercise from trained athletes on a moderate-fat (30%) diet multiplied faster than WBCs from the same athletes after spending four weeks on a low-fat (15 %) diet.
The study also found that switching from a low- to moderate-fat diet dramatically increased the number of natural killer cells, said Jaya T. Venkatraman, PhD, SUNY Buffalo assistant professor of nutrition and lead researcher of the study.
Blood analysis of the seven men and seven women athletes showed that secretion of interleukin 2 (IL2) protein, which is known to enhance immune function, increased when runners went from a low- to moderate-fat diet. IL2 levels decreased slightly when runners increased dietary fat from moderate to high, but still remained higher than when they were on a low-fat diet.
"Moderate exercise enhances immune status, but when athletes exercise to the maximum, it stresses the immune system, especially when they are training heavily and don't get enough rest," said Venkatraman. "This leaves them susceptible to upper respiratory infections."
While the study dealt with 14 adult athletes, all in their mid-30s, Venkatraman speculated that the combination of a very low-fat diet and an excessive physical training regimen would more severely affect the immune systems of teenage athletes because they are still developing.
"One of the reasons for the study is to recommend a better protocol for training, rest and diet," said Venkatraman. The findings will be published in Medicine and Science of Sports and Exercise, the official journal of the American School of Sports Medicine. The study was presented earlier this year at the annual meeting of the Federation of American Societies for Experimental Biology in Washington, D.C. Also working on the study were David R. Pendergast, PhD, professor of physiology, Peter Horbath, PhD, professor of nutrition, and John Leddy, PhD, professor of sports medicine at Buffalo.
"Athletes are continually seeking the right diet and ideal protocol for increasing performance," Venkatraman said. "Immune function is an important factor. We have shown that a low-fat diet, adhered to by many competitive athletes, may not be best for the immune system, while increasing dietary fat to moderate levels improves it. Even when we raised dietary fat to 45%, there was no negative effect on the immune response."
All of the participants ran an average of 40 miles a week. They spent four weeks on three successive diets composed of 15% fat, 30% fat and 45% fat. To study the influence of the dietary-fat level and exercise on the immune response, Venkatraman collected blood samples from the 14 runners before and after they completed each diet regimen, at rest and after they performed a maximal exercise test. She found that exercise significantly increased the number of leukocytes, but when challenged in vitro, the ability of the white cells to multiply and meet the "assault" was impaired on the low-fat diet.
"The bottom line is, in highly trained athletes, a moderate-fat diet is better for the immune system and a high-fat diet doesn't hurt it," said Venkatraman. "It is one more piece of evidence that a diet very low in fat may not be beneficial for performance athletes. A lot more work needs to be done on the influence of diet and exercise on the immune function before we have a definitive answer, but so far results on a moderate- to high-fat diet have been positive."
For more information:
- Venkatraman JT, Rowland JA, DeNardin E, et. al. Influence of level of dietary lipids and exercise on immune status in athletes. Federation of American Societies for Experimental Biology Journal. 1996; 3203:556.
Editor's note: Now we have to determine if what happens to WBCs in the test tube has any relevance to what happens in real life. Until then, we can stop jogging! P. Brunell
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