Psychosocial Stress and Diet History Promote Emotional Feeding in Female Rhesus Monkeys

One proposed contributor to the recent surge in obesity prevalence is the increased availability of highly palatable foods coupled with the drive to consume these foods under stressful conditions. Studies of humans suggest that stress exposure promotes increased caloric intake and a preference for energy-dense foods, and this may be particularly true for women, as they more often show higher rates of obesity and report a higher incidence of emotional feeding relative to men. Socially housed female rhesus macaques provide a unique, ethologically relevant model for studying the effects of psychosocial stress on appetite within varying dietary environments. Macaque groups, regardless of size, are organized by a matrilineal dominance hierarchy that functions to maintain group stability. Lower ranking animals receive more aggression from higher ranking group mates and terminate these interactions by emitting submissive behavior. Subordinates have less control over their environment, and continual harassment from dominant animals results in dysregulation of the limbic–hypothalamic–pituitary–adrenal (LHPA) axis. Metabolic and anthropometric phenotypes differ between dominant and subordinate monkeys when maintained on a standard low-fat, high-fiber laboratory diet, as dominant females are more often heavier with greater fat and bone mass. Recent studies, using validated automated feeders, suggest that under conditions of a low-caloric density diet (LCD), subordinate monkeys consume similar calories but are more active during the daytime relative to dominant monkeys. However, once a highly palatable, high-caloric density diet that is high in fat and sugar (HFSD) is added to the LCD environment, subordinate females become significantly hyperphagic and exhibit significant increases in fat mass within a 2-week period. These studies also suggest a significant effect of diet history whereby subordinate animals previously exposed to the HFSD continue to be hyperphagic when returned to a LCD-only condition. Future studies are warranted to explore the long-term effects of psychosocial stress on appetite within a rich dietary environment analogous to that of humans.