NEW YORK, May 31 (Reuters Health) -- Runners who log 40 or more miles a week and who consume a diet that is very low in fat may be compromising their immune systems, results of a small new study suggest.
Levels of infection-fighting factors such as white blood cells, cytokines, and cortisol were lowest in runners when they were consuming a diet in which 17% of calories came from fat compared with time periods when their diet contained more fat, report US researchers.
Cytokines are proteins released by immune system cells to signal to each other as they fight infection, and cortisol is a steroid hormone that acts as an anti-inflammatory agent.
In the study, 14 runners ate a regular diet for a month, a diet consisting of 17% fat for a month, and a month each on a diet of 32% fat and 41% fat. The average American eats a diet where 30% of calories come from fat.
Blood tests taken from the runners showed a doubled level of natural killer cells, which attack virus-infected and tumor cells, during the period of high-fat consumption compared with the low-fat period, while levels of prostaglandin E2, which promotes inflammation, increased during the low-fat diet period, according to the report. The study results were presented by Dr. Jaya T. Venkatramen of the State University of New York at Buffalo, at the recent 4th International Society for Exercise and Immunology Symposium in Rome, Italy.
While moderate exercise gives the immune system a boost, Venkatramen said that intensive exercise may "produce excess levels of free radicals, which might place stress on the immune system."
