the dominant females ordinarily eat a little more than the subordinates. The lower-status monkeys can get as much food as they want but seem to have less of a desire to eat, perhaps because of the higher level of stress hormones in their brains.
The anxiety of constantly toadying to their social superiors seems to curb their appetites, researchers suspect, at least when their regular high-fiber, low-fat chow is on the menu.
But suppose you tempted them with the equivalent of chocolate and potato chips and ice cream? Mark Wilson, a neuroscientist at Emory University, and a team tried that experiment at Yerkes by installing feeders with a constant supply of banana-flavored pellets – not exactly Dove bars, but they had enough sugar and fat to appeal even to human palates.
Once these foods were available, the low-status monkeys promptly developed an appetite. They began eating significantly more calories than their social superiors. While the dominant monkeys dabbled in the sweet, fatty pellets just during the daytime, the subordinate monkeys kept scarfing them down after dark. ...
Another possible explanation, the one favored by the Yerkes researchers, is that the snacks activated the reward pathways in the brain. They may have provided the same sort of dopamine reward as cocaine, which was studied in a previous experiment with monkeys by researchers at Wake Forest University.
In that experiment, the dominant monkeys didn't show much interest in pressing a lever that administered an intravenous dose of cocaine. But the subordinate monkeys kept pushing the lever to get more cocaine, just as the subordinates in the new study kept munching on the fatty pellets.
Wilson suggests that the snackers are reinforcing the dopamine systems that had been diminished by stress.
“Essentially, eating high-calorie foods becomes a coping strategy to deal with daily life events for an individual in a difficult social situation,” Wilson said. “The subordinates don't get beat up, but they get harassed by high-ranking monkeys. If they're sitting somewhere and a dominant monkey comes over, they give up their seat and move away. They're always looking over their shoulders.”
These results seem to jibe with the famous Whitehall study of British civil servants, which found that lower-ranking workers were more obese than higher-status workers. Even though the subordinate workers were neither poor nor lacking in health care, their lower status correlated with more health problems.
The new monkey data also jibe with an American study that looked at women's snacking tendencies. After they worked on puzzles and recorded a speech, the women in the study were tempted with an array of chocolate granola bars, potato chips, rice cakes and pretzels provided by the research team, led by Elissa Epel, a psychologist at the University of California San Francisco.
The women who seemed most stressed by the tasks, as measured by their levels of cortisol, ate more of the sweet, high-fat snacks – the same pattern observed in the subordinate monkeys with high cortisol levels.
Thursday, May 22, 2008
Comfort Foods and Stress
Comfort foods seem to be a reaction to stress for the low status monkeys in these experiments.