Comfort Food, for Monkeys is John Tierney’s article today, reporting on recent research by Mark Wilson and colleagues at Yerkes Primate Center about rhesus monkeys, sweet tooths, social stress and inequality. Familiar themes, all of them.

Normally, low-status monkeys eat roughly the same amount of bland monkey chow as dominant individuals. But add sweet banana-flavored pellets to the mix, and suddenly the equation changed: “While the dominant monkeys dabbled in the sweet, fatty pellets just during the daytime, the subordinate monkeys kept scarfing them down after dark.”

Tierney goes on to outline reasons why this scarfing vs. dabbling dynamic might emerge in socially complex species like rhesus monkeys. As Wilson et al. note in their paper, “this ethologically relevant model may help understand how psychosocial stress changes food preferences and consumption leading to obesity.”

Tierney describes research by Dallman et al., who have proposed that people can directly impact stress hormones through eating, largely by mediating anxiety: “[P]eople eat comfort food in an attempt to reduce the activity in the chronic stress-response network with its attendant anxiety.” So individuals with greater stress reactivity and negative mood tend to eat more in their stressed vs. control experimental paradigm.

As Tierney notes with a quip about a “stressed-out wage slave who has polished off a quart of Häagen-Dazs at midnight while contemplating the day’s humiliations,” inequality can bring on stress reactivity and negative mood (for more on that, see previous stress and inequality posts on Sapolsky and Blakey). In turn, inequality feeds into the obesity epidemic through both social and cultural dynamics.

But Tierney also knows that seeking food, not simply reactive eating, is key to overall weight gain. He mentions work by Morgan et al. on social inequality, dopamine, and addiction, covered in greater detail here. The short summary is that social subordinate monkeys both have lower dopamine levels and binge on cocaine.

Mark Wilson makes a similar argument about fat, sugary food: “Essentially, eating high-calorie foods becomes a coping strategy to deal with daily life events for an individual in a difficult social situation. 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.”

One missing piece in Tierney’s consideration is that sugar can act to directly reinforce the dopamine system, rather than just the psychosocial stress angle. Together, reinforcement and stress can become canalized into a vicious cycle.

A central part of this cycle is the sociocultural angle, which Tierney briefly covers early in the article:

Monkeys’ cravings aren’t so complicated. The female monkeys weren’t dieters who tasted one forbidden food and then couldn’t stop themselves from binging. They were not rebelling against the thin mandate from tyrannical fashion magazines. They weren’t choosing junk food because they couldn’t find healthier fare. They weren’t seduced by commercials telling them they deserved a break today.

The cultural mandates of beauty, when coupled to the evolution of self control, can facilitate the restraint and binge dynamic. This combination provides a more dynamic consideration of the last research mentioned by Tierney. In a study on gender and snacking behavior, Debra Zellner found that men snack more when not under stress and women while under stress. “Female humans report that they eat high-calorie foods to make themselves feel better when stressed,” Dr. Zellner says, “but they actually don’t feel better after eating them. Instead, because they are restrained eaters, they feel guilt and actually feel worse. Female monkeys don’t have that cognitive baggage.”

That cognitive baggage is better thought of as embodied baggage, where ideals of beauty, practices of restraint, and stress and dopamine all come together in ways that can lead to scarfing down snack foods. Unlike the rhesus monkeys, where the stress is largely mediated by the hierarchy, we humans can internalize our mix of ideals and status, and that then plays into our overall brain function, behavior, and sense of self.