23 May 1999
Very-low-fat Diet May Compromise Immunity
Athletes who severely limit the amount of fat in their diets may be suppressing their immune system and increasing their susceptibility to infections and inflammation, a University at Buffalo study has shown.
In findings presented at the fourth International Society for Exercise and Immunology Symposium, lead author Jaya T. Venkatraman, Ph.D., reported that running 40 miles per week on a diet composed of approximately 17 percent fat hinders the runners' immune response.
The medium and high-fat diets, composed of approximately 32 and 41 percent fat respectively, left the immune system intact, and enhanced certain components, the findings showed.
"The data suggest that higher-fat diets may lower the proinflammatory cytokines, free radicals and hormones, and may enhance the levels of anti-inflammatory cytokines," Venkatraman said.
Earlier studies published by a UB research group headed by David Pendergast, Ed.D., professor of physiology and biophysics, reported that competitive runners who increased the proportion of fat in their diets improved their endurance with no negative effect on weight, body composition, blood pressure, pulse rate or total cholesterol.
However, since a high level of fat was thought to be immunosuppressive, the researchers sought to determine if increasing dietary fat would compromise various elements of the immune system, while improving performance.
"In general, moderate levels of exercise are known to enhance the immune system," said Venkatraman. "But high-intensity exercise and endurance exercise produce excess levels of free radicals, which may place stress on the immune system.
"Since we have shown that athletes perform better on a higher-fat diet than on a low-fat diet, it was important to determine if the higher-fat diet would further compromise the immune system," she said. "We found that it did not, but the very-low-fat diet did."
The study involved six female and eight male competitive runners who trained at 40 miles a week and were part of a larger performance study. They spent a month on their normal diets, followed by a month each on diets composed of approximately 17 percent, 32 percent and 41 percent fat. Protein remained stable at 15 percent and carbohydrates made up the difference.
The immune status of the runners was obtained by analyzing concentrations of essential components of the immune system - leukocytes, cytokines and plasma cortisol - in blood samples taken before and after an endurance exercise test. The tests were conducted at the end of each four-week diet period.
Results showed that natural killer cells, a type of leukocyte and one of the body's defense mechanisms marshaled to fight infection, were more than doubled in runners after the high-fat diet, compared to the low-fat regimen. Levels of PGE2, inflammation-causing prostaglandins, increased after the endurance test and were higher when the runners were on the low-fat diet.
This study is part of a larger investigation to determine the effects of dietary fat on performance, biochemical and nutritional status, and plasma lipids and lipoprotein profiles in distance runners being conducted by a study group at the University of Buffalo.