Their research showed that white-blood cells collected after maximum exercise from trained athletes on a moderate-fat-30 percent-diet multiplied faster than white-blood cells from the same athletes after spending four weeks on a low-fat-15 percent-diet. White-blood cells, or leukocytes, are the body's infection fighters.

In addition, moving from a low- to moderate-fat diet dramatically increased the number of natural killer cells, said Jaya T. Venkatraman, UB assistant professor of nutrition and lead researcher on the study.

Blood analysis showed that secretion of a protein called interleukin 2 or IL2, 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 on a low-fat diet. Study results were presented this month at the annual meeting of the Federation of American Societies for Experimental Biology.

"Athletes are continually seeking the right diet and ideal protocol for increasing performance," she 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 percent, there was no negative effect on the immune response."

Venkatraman's subjects were seven men and seven women who were part of the larger UB study investigating the effect of different diets on performance and cardiovascular risk factors in trained runners. All participants ran an average of 40 miles a week; some were top-ranked regionally. They all spent four weeks on three successive diets composed of 15 percent fat, 30 percent fat and 45 percent fat, respectively.

To study the influence of 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.

"Moderate exercise enhances immune status," said Venkatraman, "but when athletes exercise to the maximum, it stresses the immune system. This leaves them susceptible to upper respiratory infections. It is one more piece of evidence that a diet very low in fat may not be beneficial for performance athletes."

Other researchers were Jill Rowland, a master's candidate in UB's Nutrition Program, Ernesto G. DeNardin, assistant professor of oral biology; Peter J. Horvath, associate professor of nutrition and physiology, and David R. Pendergast, professor of physiology.