Diet choice, cortisol reactivity, and emotional feeding in socially housed rhesus monkeys

Abstract

Chronic psychosocial stress produces an array of adverse health consequences that are highly comorbid, including emotional eating, affective disorders, and metabolic syndrome. The consumption of high caloric diets (HCDs) is thought to provide comfort in the face of unrelenting psychosocial stress. Using social subordination in female rhesus monkeys as a model of continual exposure to daily stressors in women, we tested the hypothesis that subordinate females would consume significantly more calories from a HCD compared to dominant females, and this pattern of food intake would be associated with reduced cortisol release and reduced frequency of anxiety-like behaviors. Food intake, parameters of cortisol secretion, and socio-emotional behavior were assessed for 3 weeks during a no choice phase when only a low caloric diet (LCD) was available and during a choice condition when both a LCD and HCD were available. While all animals preferred the HCD, subordinate females consumed significantly more of the HCD than did dominant females. A flattening of the diurnal cortisol rhythm and a greater increase in serum cortisol to an acute social separation occurred during the diet choice condition in all females. Furthermore, the rate of anxiety-like behavior progressively declined during the 3-week choice condition in subordinate but not dominant females. These data provide support for the hypothesis that daily exposure to psychosocial stress increases consumption of calorically dense foods. Furthermore, consumption of HCDs may be a metabolic stressor that synergizes with the psychosocial stress of subordination to further increase the consumption of these diets.

Figure 1

Mean ± SEM rates of aggressive behavior received and submission behavior emitted in females at each social dominance rank throughout the course of the study. Rates of aggression received and submission emitted were significantly higher (p < 0.002) in animals categorized as subordinate females (ranks 3 – 5) compared with those categorized as dominant (ranks 1 and 2).

Figure 2

Mean daily kcal consumed (± SEM) by dominant and subordinate females during three weeks of the no choice condition when only the LCD was available (open bars) and the three-week choice condition when the LCD (open bars) and HCD (closed bars) were available. “NS” indicates the indicated comparison was not significant (p > 0.05).

Figure 3

Panel A shows mean ± SEM serum diurnal cortisol (μg/dl) concentrations at 0730, 1200, 1800 hours during week two of each diet phase for dominant (open bars) and subordinate females (closed bars). The dashed line above the bars for the 1800 hr time point for the no choice condition illustrates the mean of serum cortisol for the 1800 hr time point for the choice condition. Panel B shows the change in serum cortisol from 0730 to 1800 hr for both diet conditions, collapsed across dominance status. “NS” indicates the indicated comparison was not significant (p > 0.05).

Figure 4

Panel A shows the mean ± SEM serum cortisol levels (μg/dl) prior to the separation (“Baseline”), immediately following a 40 minutes social separation (“Post stress”), and 2.5 hours after being returned to the group (“Recovery”) for the dominant (open bars) and subordinate monkeys (closed bars) during both the no choice and choice phases. Different letters indicate time points are significantly different (post-hoc test, p < 0.001) within each diet condition. “NS” indicates the interaction of status, time, and diet condition in serum cortisol during the social separation test was not significant (p > 0.05). Panel B shows the change in serum cortisol from baseline to post stress samples for both diet conditions, collapsed across dominance status.

Figure 5

Mean ± SEM frequency of aggressive behavior directed at cage mates by dominant (open bars) and subordinate females (closed bars) during the no choice and choice conditions. Asterisk indicates that aggressive behavior in dominant females was significantly higher during week 2 compared with weeks 1 and 3 during both diet conditions.

Figure 6

Mean ±SEM of anxiety-like behavior by dominant (open bars) and subordinate females (closed bars) during both the no choice and choice conditions. Different letters indicate significant status differences in rates of anxiety (post-hoc test, p < 0.02). “NS” indicates the indicated comparison was not significant (p > 0.05).

Figure 7

Mean ±SEM of the frequency of affiliative behavior directed at cage mates (panel A) and the durations of these behaviors (panel B) by dominant (open bars) and subordinate females (closed bars) during both the no choice and choice conditions. Different letters indicate time points are significantly different (post-hoc test, p < 0.05). Asterisk indicates that affiliative behavior directed to others by dominant females was significantly higher during week 2 compared with weeks 1 and 3 during both diet conditions. “NS” indicates the indicated comparison was not significant (p > 0.05)