Effects of Feeding (or Fasting) on Stress Responses

Although stress alters food intake regulation, the absence of food (fasting or starvation) is itself a stressful event. For instance, stress hormones and CRH (anorexigenic) are chronically increased in anorexia nervosa patients, which may contribute to the difficulty these patients experience in trying to reverse their illness.

Stress from absence of food is, however, different from stressors such as restraint stress. Glucocorticoid receptors (GRs) in the hypothalamus are downregulated following chronic, repeated restraint, thus decreasing negative feedback on CRH mRNA in the PVN. The decreased inhibition of CRH mRNA results in fewer anorexigenic effects of the PVN CRH during starvation. Furthermore, the ACTH response to stress is altered during fasting.

Not only does the absence of food change stress responsivity, but eating palatable (e.g., sugar- and fat- containing) food also changes the response to stress. Rats that voluntarily choose the percentage of lard in their diets (composing their own high-fat diet) have reduced HPA responses to restraint stress; however, when forced to eat a high-fat diet the response of the HPA axis to restraint is high or similar compared to rats that consume only chow.

Some controversy exists regarding the stress responsivity when animals are eating a high-fat diet. Although the choice to eat fat seems important for the response to stress, rats that were force-fed a high-fat diet for a longer time did have decreased responses in activity and body temperature when socially stressed (social defeat).

Concluding Remarks. Stress clearly affects the neural circuitry regulating food intake at several levels. Some people react to stress by overeating, which contributes to the development of obesity, whereas others (e.g., anorexia nervosa patients) reduce their food intake. Differences in these coping strategies may originate in subtle differences between individuals in the neural circuitry underlying food intake and stress.

A better insight into how the stress system interacts with the food intake circuitry, as well as into the mechanism underlying individual responsiveness to stress, is necessary to find new strategies to treat eating disorders such as obesity and anorexia nervosa. The type of diet also affects the stress response. Future research is needed to understand the mechanisms underlying how palatable food interacts with the neural circuitry of the stress response.