Effects of dietary fat and endurance exercise on plasma cortisol, prostaglandin E-2, interferon-gamma and lipid peroxides in runners

Objective: Exercise and the neuroendocrine and oxidative stress it elicits on immune function is modulated by dietary fat intake. The effects of incre asing dietary fat on endurance exercise-induced alterations (80% of (V) ove r dot O-2max. for 2 hours) in the plasma levels of cortisol and prostagland in E-2 (PGE(2)), interferon-gamma (IFN-gamma) and lipid peroxides were inve stigated. As higher levels of cortisol, PGE(2) 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 e ach. In the last week of each diet period the subjects ran to exhaustion at 80%, of their (V) over dot O-2max and blood was drawn pre- and post-run. C ortisol, IFN-gamma, PGE(2) and lipid peroxides were determined using standa rd techniques. Results: Pre-exercise levels of plasma cortisol were elevated, IFN-gamma wa s unchanged and PGE(2) and lipid peroxides decreased on the 40%F diet compa red to 30%F and 15%F. Post-exercise levels of plasma cortisol (p < 0.004), PGE(2) (p < 0.0057) and lipid peroxide levels increased (p < 0.0001) after endurance exercise on all diets. The rates of increase of plasma cortisol l evels during exercise were similar on all three diets. Although absolute co rtisol levels were higher in the high fat group, the rate of increase of pl asma cortisol level during exercise was similar on each diet, The dietary f at levels did not affect IFN-<gamma>, however, PGE(2) and lipid peroxides d ecreased 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 eff ects on plasma cortisol, IFN-<gamma>, and lipid peroxide levels.