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Brain may sabotage effort to diet

Posted Nov 21 2011 12:00am
When lean people have full stomachs, neural signals cause their brains to stop wanting food. The positive feelings associated with food are turned off. But a new study from Yale reports that the brains of obese people react to food differently.

Willpower and reasoning
In this study, 9 lean and 5 obese adult volunteers underwent brain scans while looking at pictures of foods such as ice cream, french fries, cauliflower, or a salad. All the volunteers arrived for the first scans with empty stomachs and relatively low blood sugar, and all of them reported wanting the food in the pictures, especially the high-calorie food. For all 14 hungry volunteers, the scans showed that the brain areas that control positive reinforcement and desire for food were active and turned on, but the parts of the brain associated with willpower and reasoning, such as the prefrontal cortex, were not active. No surprise there. When we're hungry, food is attractive and eating feels good. And we're reluctant to stop until the hunger is gone.

Unexpected findings
The interesting part of the study occurred when the volunteers arrived full and sated, with normal blood-sugar levels. It turns out, the brain scans of the obese volunteers were the same whether they were full or hungry. The part of the brain that controls desire for food and regards food as positive reinforcement were still active even when their stomachs were full. And the part of the brain that regulates willpower and reasoning was still inactive even when they were full.

In contrast, the brain scans of the lean volunteers with full stomachs showed a decrease in their desire for food, and higher activity in the part of the brain associated with reasoning and willpower.

Implications are huge
Yale endocrinologist Robert Sherman, coauthor of the new study, says the surprise was that the part of the brain that regulates willpower over eating was mostly turned off in obese people, regardless of hunger and blood-sugar levels. The implications of this study are enormous. Coauthor Sherman says the findings suggest that brain functions "may perpetuate obesity."

So what now?
What's the solution? Most weight-loss programs say keep the high-calorie foods out of the house. If we have to nibble, we should go after the fruits and vegetables. That's not so easy this time of year, with all the attention to holiday foods. We can't control what shows up on the platters at holiday gatherings. But it may be a little easier to control what we keep in our kitchens.
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