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Brain Differences in Response to Foods and Obesity Tied to Gender

ARTICLE IN BRIEF

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A new neuroimaging study suggests that the female brain may be designed to make it more difficult to stop eating.

The wiring of the human brain may actually give men an upper hand in saying “no” to tempting food, according to a new study by scientists at Brookhaven National Laboratory.

Gene-Jack Wang, MD, and his colleagues have spent the past decade studying the triggers of over-eating. The latest study, published in the Jan. 27 Proceedings of the National Academy of Sciences, suggests that the female brain may be designed to make it more difficult to stop eating, a throwback to ancient times when feast or famine was a matter of life and death.

Dr. Wang brought 23 hungry, average-sized adults into the laboratory in Upton, NY, and showed them 10 favorite foods one at a time in a two-day testing period. The volunteers could see, smell, and talk about the food in front of them, but no eating was allowed. (They hadn't eaten for at least 17 hours.) A cotton swab introduced the taste of the food onto the tongue.

They rated their hunger and desire for the food, and minutes later, were scanned with PET and a tracer to measure glucose metabolism in the brain when their desired foods were shown. All said, they were hungrier after seeing favorite foods, which was confirmed by the brain activity in the scans.

According to Dr. Wang, the somatosensory cortex, which is active in perceiving taste, became active. The insula, an area thought to be involved in appetite, also became active.

On day two, the subjects were instructed to see, smell, and talk about the same 10 foods but they were told to inhibit their desire for the food by saying “no” to the thoughts that drive the penchant for the foods. They rated their ability to squelch their desire and were scanned with PET.

In comparing scans and self-reports from people who reported feeling most hungry on day one of the study and their baseline assessment, the investigators found that the hungriest among them showed the most robust changes in the orbitofrontal cortex. When the men and women were asked to inhibit thoughts and desires for food, both sexes reported their feelings of hunger were diminished but the brain scans revealed a different picture: men had an easier time inhibiting their desire for food.

The cognitive inhibition in men resulted in a decrease in activation of limbic and paralimbic regions; in women, cognitive inhibition did not affect regional brain metabolism. Specifically, the men showed significant activation decreases in the left amygdala, left hypothalamus, left orbitofrontal cortex, left uncus, right striatum, right insula, anterior cingulate gyrus, parahippocampus, and cerebellum — areas associated with emotional regulation, conditioning and motivation. They also found the association between suppression of orbitofrontal activation and hunger in men, which corroborates the involvement of this region in processing motivation for food consumption.

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According to Dr. Wang, the whole feeding circuit in men was turned down.

When women said that they were suppressing their desire for their favorite foods shown to them, their effort did not show up on the brain scans. “The signal is too much for women,” Dr. Wang jokes. But he also recommends some lifestyle factors that can influence the energy balance of the brain. He said that exercise increases brain activity in regions that could reduce the desire to eat too much.

He added that the findings suggest that dietary treatments must take into account the gender issue. This latest study included people of average weight and the brain of an obese person may be wired differently, he said. Dr. Wang suspects that people who overeat may have an altered, perhaps exaggerated, response in these same regions. The scientists had previously found that obese people have about 14 percent fewer dopamine receptors in the striatum. They believe this deficit of receptors may trigger overeating to stimulate “reward and motivation” circuits and might trigger overeating in an effort to stimulate cerebral “reward and motivation” circuits. The Brookhaven scientists have seen similar patterns in drug addicts.

Charles Billington, MD, an eating disorders specialist in Minnesota, said that the findings are intriguing and make sense. “In most cases, people who treat obesity try using education to strengthen cognitive facilities but these methods fail because we still have to grapple with basic brain functions that regulate appetite.”

Dr. Billington, associate director of the Minnesota Obesity Center and professor of medicine at the University of Minnesota, said that the evidence is mounting that “the desire and the decision to eat or not eat takes place in older brain regions, including the emotional centers. People have problems reigning in their desire because of the strength of these brain networks.” He said that the gender differences will need to be replicated in other studies before people begin designing gender-based strategies for weight loss.

REFERENCES

• Wang GJ, Volkow ND, Fowler JS, et al. Evidence of gender differences in the ability to inhibit brain activation elicited by food stimulation. Proc Natl Acad Sci USA 2009;106(4):1249–1254. E-pub 2009 Jan 21.
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