Behavioral and physiological responses to stress are affected by high-fat feeding in male rats

Interactions between monoaminergic neurochemistry and macronutrient intake have been frequently shown. Because monoaminergic systems in the brain are also closely involved in behavioral and physiological stress responses it can be hypothesized that differences in the macronutrient composition of diets are reflected in these responses. The present studies, therefore, were designed to assess the consequences of a change in dietary macronutrient composition on a variety of physiological and behavioral responses (both acute and long-term) to a number of stressors. The effect of chronic high-fat (HF; 61% kcal from fat) feeding on the stress responses was compared with controls receiving regular high-carbohydrate (HC; 63% kcal from carbohydrates) laboratory chow. Rats were kept on this diet for at least 2 months before they were exposed to either psychological (social defeat) or physiological (lipopolysaccharide, LPS, administration) stress. At baseline, chronic HF feeding caused a slight, but significantly reduction in body temperature relative to that observed in HC-fed rats. Following social defeat or LPS injection, HF feeding caused a faster recovery of the body temperature increase relative to animals on the HC diet. Stress-induced suppression of home cage locomotor activity and body weight gain were also reduced by HF feeding. The serotonergic 5-HT(1a) receptor hyposensitivity that was observed in HC-fed rats 2 weeks after stress was absent in the HF regimen. Although the present results cannot be readily interpreted as showing purely beneficial effects of high-fat diets on stress responsivity, the findings in the present study do encourage further investigation of possible ameliorating effects of high-fat diets on aspects of the behavioral and physiological response stress.