In lab experiment, they fail to connect color signal with tasty reward
Obese women have a blind spot, but only when food is in the picture. In laboratory tests, obese women had trouble learning an association between a colored screen and a reward of M&M’s or pretzels, scientists report July 17 in Current Biology.
This deficit occurred only for obese women, and not obese men or people who were not overweight. It was also specific to food: The women easily made the connection when the reward was money. The results suggest that in some cases, abnormal responses to food rewards might contribute to obesity, says neuroscientist Nicole Avena of Columbia University, who was not involved in the research.
The study also provides an intriguing glimpse into men and women’s distinct responses to food. “We know that there are big differences between males and females with regard to lots of different behaviors,” Avena says. “There’s no reason to think that obesity and overeating wouldn’t be one of them.”
Scientists led by Ifat Levy, a neuroscientist at Yale University, recruited 67 participants of normal weight and 68 who were obese for a learning experiment. In a lab, participants saw one of two colors, either blue or purple, flash on a screen. About a third of the time, one of the colors would be followed with an image of either a food treat or money. The other color was never followed by a reward.After the experiment, participants received the snack or cash they had seen in the photos.
By asking participants how much they expected to receive as a reward each time they saw one of the two colors, the researchers got a sense of how well people learned the association. At the outset, “we didn’t expect a gender difference at all,” says Levy. But one certainly showed up. Obese women, but not obese men or participants of normal weight, had a hard time telling which color signaled a food reward, the team found. And their impairment came in an unexpected way: These women knew when a particular color was tied to a treat. The problem was that they often thought that the other color, the one not associated with food, would also lead to a reward.
“As soon as there is food in the environment, it affects everything,” Levy says. And that tendency may have evolved for good reason: Forming food associations even when there are none might have been beneficial in an environment with scant resources, she says. “When there is an indication of food in the environment, you generalize it because it’s important to get as much food as possible.”
The study finds a link between obesity and impaired food-related learning, but it can’t say anything about cause, Levy says. Scientists are finding clues that obesity itself can influence how a person thinks and makes decisions. But learning deficits like those uncovered in the study may also lead to overeating.
Obesity researcher Allan Geliebter, of Mount Sinai St. Luke’s hospital in New York, says the study “raises questions but I don’t think it gives us too many answers.” Future studies, such as those that test obese people’s learning with healthful snacks, could offer a deeper understanding of how people respond to food cues, he says.
Z. Zhang et al. Impaired associative learning with food rewards in obese women. Current Biology. Vol. 24, August 4, 2014. doi: 10.1016/j.cub.2014.05.075.
L. Sanders. Brain’s support cells play role in hunger. Science News. Vol. 185, June 28, 2014, p. 10.