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It’s well established that people with low economic status are the hardest hit by the current obesity pandemic, as well as related health problems such as diabetes. Poor healthcare, stress, unhealthy lifestyles, and a cornucopia of cheap junk food are all thought to play a role. But a new study suggests there’s a subconscious component, too.

When researchers merely prompted study volunteers to consider themselves low-class, they were more likely to prefer, choose, and eat larger amounts of food, as well as higher-calorie foods. The findings, published in the Proceedings of the National Academy of Sciences, echo what’s been seen in a variety of animals—from birds and rodents to nonhuman primates. Thus, the authors speculate that the mental glitch may be an evolutionary holdover intended to boost survival by compensating for a lack of social and material resources.

More important for humans, the findings suggest that we may not be able to tackle obesity by just improving access to healthier foods and promoting exercise.

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