Effects of Dietary Fat and Endurance Exercise on Plasma Cortisol, Prostaglandin E2, Interferon-gamma and Lipid Peroxides in Runners

Jaya T. Venkatraman, PhD, CNS, FACN, Xiaohong Feng, MS, and David Pendergast, EdD

Department of Physical Therapy, Exercise and Nutrition Sciences (J.T.V., X.F.), Department of Physiology (D.P.), State University of New York at Buffalo, Buffalo, New York [jtv@acsu.buffalo.edu]

Objective: Exercise and the neuroendocrine and oxidative stress it elicits on immune function is modulated by dietary fat intake. The effects of increasing dietary fat on endurance exercise-induced alterations (80% of VO_2max for 2 hours) in the plasma levels of cortisol and prostaglandin E₂ (PGE₂), interferon-gamma (IFN-gamma) and lipid peroxides were investigated. As higher levels of cortisol, PGE₂ and lipid peroxides could be immunosuppressive, the effects of different levels of dietary fat on these measures in runners were determined.

Methods: Healthy trained runners (males and females) consumed serially 15% fat diet (of daily energy), 30% fat diet and 40% fat diets for four weeks each. In the last week of each diet period the subjects ran to exhaustion at 80% of their VO_2max and blood was drawn pre- and post-run. Cortisol, IFN-gamma, PGE₂ and lipid peroxides were determined using standard techniques.

Results: Pre-exercise levels of plasma cortisol were elevated, IFN- was unchanged and PGE₂ and lipid peroxides decreased on the 40%F diet compared to 30%F and 15%F. Post-exercise levels of plasma cortisol (p<0.004), PGE₂ (p=0.0057) and lipid peroxide levels increased (p<0.0001) after endurance exercise on all diets. The rates of increase of plasma cortisol levels during exercise were similar on all three diets. Although absolute cortisol levels were higher in the high fat group, the rate of increase of plasma cortisol level during exercise was similar on each diet. The dietary fat levels did not affect IFN-gamma, however, PGE₂ and lipid peroxides decreased with increasing fat at baseline at 40%F level (p< 0.01; 30%F vs. 40%F: p< 0.002; 15%F vs. 40%F: p< 0.007).

Conclusions: Data from the present study suggest that higher levels of fat in the diet, up to 40%, increase endurance running time without adverse effects on plasma cortisol, IFN-gamma, and lipid peroxide levels.