Quantifying food intake in socially housed monkeys: social status effects on caloric consumption

Abstract

Obesity results from a number of factors including socio-environmental influences and rodent models show that several different stressors increase the preference for calorically dense foods leading to an obese phenotype. We present here a non-human primate model using socially housed adult female macaques living in long-term stable groups given access to diets of different caloric density. Consumption of a low fat (LFD; 15% of calories from fat) and a high fat diet (HFD; 45% of calories from fat) was quantified by means of a custom-built, automated feeder that dispensed a pellet of food when activated by a radiofrequency chip implanted subcutaneously in the animal's wrist. Socially subordinate females showed indices of chronic psychological stress having reduced glucocorticoid negative feedback and higher frequencies of anxiety-like behavior. Twenty-four hour intakes of both the LFD and HFD were significantly greater in subordinates than dominates, an effect that persisted whether standard monkey chow (13% of calories from fat) was present or absent. Furthermore, although dominants restricted their food intake to daylight, subordinates continued to feed at night. Total caloric intake was significantly correlated with body weight change. Collectively, these results show that food intake can be reliably quantified in non-human primates living in complex social environments and suggest that socially subordinate females consume more calories, suggesting this ethologically relevant model may help understand how psychosocial stress changes food preferences and consumption leading to obesity.

Figure 1

Mean ± sem plasma cortisol concentrations aligned from hours from a dexamethasone (Dex) injection. An asterisk indicates a significant difference (P < 0.05) between dominant (open bar) and subordinate females (black bar) at a specific time point.

Figure 2

Mean ± SEM kcal per kg per day consumed by dominant and subordinate females during three-week access to a LFD and a three-week access to a HFD diet. Data illustrate daytime (0600 – 1759 hr) and nighttime (1800 – 0559 hr) food intake. An asterisk indicates values at a specific time point are significantly different between dominant and subordinate females (p < 0.05).

Figure 3

The linear relation, reflected by the coefficient of determination between a female’s social rank (1 through 5) and the number of kcal consumed during solitary access to a LFD (open symbol) and access to a HFD diet (closed symbol).

Figure 4

The linear relation, reflected by the coefficient of determination, between the change in body weight and the number of kcal consumed by a female during three-week access to a LFD (open symbol) and a three-week access to a HFD diet (closed symbol).

Figure 5

Mean ± sem kcal per kg per day consumed of the LFD and the HFD by dominant and subordinate females when Purina monkey chow was available ad libitum (right panel) and when it was unavailable (left panel). Each of the four phases (LFD alone or with the Purina diet and HFD alone or with the Purina diet) were one week in length. Data illustrate daytime (0600 – 1759 hr) and nighttime (1800 – 0559 hr) food intake. An asterisk indicates values at a specific time point are significantly different between dominant and subordinate females (p < 0.05). Significantly more of the LFD and HFD were consumed when the Purina diet was unavailable.