When food's the reward, obese women's judgment fails them

Obese women appear to have a very specific impairment when tasty food is present

At the risk of inspiring offensive commentary from misogynists and fat haters, I bring you this intriguing finding about obese women from researchers at Yale University: Compared to their normal-weight peers, obese women -- but not men -- appear to have a highly specific learning deficit around the issue of food.

When a tasty reward is dangled before them, obese women's powers of learning and decision-making appear to get short-circuited in a way not seen in women of normal healthy weight, or in men of any weight, a new study shows. When it comes to maximizing a monetary payout, however, these same women are every bit as sharp as their thinner peers or any male peer.

The research, published this week in the journal Current Biology, may be taken by some as evidence to support the broad stereotype of the obese -- and especially obese women -- as stupid, sad and self-defeating, a view widely held even by physicians who treat such patients. But the study's senior author suggests instead that the perceptual impairment identified by the study is narrow indeed: Take tasty food out of the equation, and these obese women are as cognitively nimble as anyone else, says Yale University's Ifat Levy.

Moreover, adds Levy, it may be possible to correct the specific cognitive weakness seen in obese women with some behavioral intervention, starting with training to compensate for this specific cognitive weakness. But first, she notes, it must be seen for what it is.

This finding emerged from a test of "associative learning," in which 135 subjects were shown a sequence of blue squares and purple squares and essentially asked to guess which square was more likely to yield a reward. The pattern of rewards was not random: On any given sequence, a square of one color had a moderate likelihood of a payout, while the other paid none.

As players discerned that pattern, they could accumulate winnings. Midway through the exercise, researchers reversed the reward scheme, and players smart enough to detect that the rules had changed could maximize their earnings.

When the promised stakes were monetary (with dollar signs superimposed on the blue and purple squares), obese women had no difficulty in accurately discerning a fixed pattern of rewards, and of responding appropriately when that pattern changed. They were no less mentally nimble than men were, or than svelte women were. And they accumulated, on average, equal winnings.

But when researchers superimposed pictures of pretzels or peanut M&M candies on the squares, and held out those treats as rewards for deducing the reward system, the cognitive powers of women whose body mass index averaged roughly 37 (for instance, a 5-foot-5 woman weighing about 220 pounds) crumbled.

When induced by edible treats in this game of pattern recognition, normal-weight women had no problem figuring out the reward system. Men too -- regardless of weight -- quickly perceived the pattern. When the researchers switched up the pattern in the middle of the game, the men and the normal-weight women responded nimbly: When they discerned that the reward patterns had reversed, they quickly shifted too.

But the obese women were so flummoxed when the promise of treats was dangled over them that not one of 17 such subjects recognized the pattern of rewards so evident to everyone else (in all, 136 subjects -- men, women, obese and not obese -- participated). When the pattern of rewards was reversed, these women were just as flummoxed, and did not discern a change. Whether the square they were shown was blue or purple, if it had a little picture of M&Ms or pretzels on it, the obese women tended to judge them all as equally likely to yield a reward.

Levy and her co-authors, Zhihao Zhang, Kirk F. Manson and Daniela Schiller, note that the same learning impairment is evident in non-human animals who are obese. They caution that it's not at all clear whether this distorted judgment causes obesity, or whether a diet high in fat and sugar causes this distorted judgment. (Another possibility: Obesity and a diet that constantly lights up the brain's reward circuits reinforce each other, causing a cycle that's hard to break).

Levy says it will take more research to discern that pattern and to explore what types of training or cognitive therapy might be helpful to obese women who want to overcome this learning impairment and lose weight.

"With training, would they have been different? It's certainly something I'd love to try," said Levy, an assistant professor at Yale School of Medicine.

Watching the nation's weigh as well as your own? Follow me on Twitter @LATmelissahealy.

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