Brain-Imaging Study May Explain Why Some Overweight People Continue To Eat, Despite Full Stomachs

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Brain-Imaging Study May Explain Why Some Overweight People Continue To Eat, Despite Full Stomachshttp://www.medicalnewstoday.com/articles/93595.php

Researchers at the U.S. Department of Energy's Brookhaven National

Laboratory have found new clues to why some people overeat and gain

weight while others don't. Examining how the human brain responds to

" satiety " messages delivered when the stomach is in various stages of

fullness, the scientists have identified brain circuits that motivate

the desire to overeat. Treatments that target these circuits may prove

useful in controlling chronic overeating, according to the authors. The

study is published online and will appear in the February 15, 2008

issue of NeuroImage.

" By simulating feelings of fullness with an expandable balloon we saw

the activation of different areas of the brain in normal weight and

overweight people, " said lead author Gene-Jack Wang of Brookhaven Lab's

Center for Translational Neuroimaging. The overweight subjects had less

activation in parts of the brain that signal satiety in normal weight

subjects. The overweight subjects were also less likely than normal

weight subjects to report satiety when their stomachs were moderately

full. " These findings provide new evidence for why some people will

continue to eat despite having eaten a moderate-size meal, " said Wang.

Wang and colleagues studied the brain metabolism of 18

individuals with body mass indices (BMI) ranging from 20 (low/normal

weight) to 29 (extremely overweight/borderline obese). Each study

participant swallowed a balloon, which was then filled with water,

emptied, and refilled again at volumes that varied between 50 and 70

percent. During this process, the researchers used functional magnetic

resonance imaging (fMRI) to scan the subjects' brains. Subjects were

also asked throughout the study to describe their feelings of fullness.

The higher their BMI, the lower their likelihood of saying they felt

" full " when the balloon was inflated 70 percent.

One notable region of the brain - the left posterior amygdala

- was activated less in the high-BMI subjects, while it was activated

more in their thinner counterparts. This activation was turned " on "

when study subjects reported feeling full. Subjects who had the highest

scores on self-reports of hunger had the least activation in the left

posterior amygdala.

" This study provides the first evidence of the connection of

the left amygdala and feelings of hunger during stomach fullness,

demonstrating that activation of this brain region suppresses hunger, "

said Wang. " Our findings indicate a potential direction for treatment

strategies - be they behavioral, medical or surgical -- targeting this

brain region. "

The scientists also looked at a range of hormones that

regulate the digestive system, to see whether they played a role in

responding to feelings of fullness. Ghrelin, a hormone known to

stimulate the appetite and cause short-term satiety, showed the most

relevance. Researchers found that individuals who had greater increases

in ghrelin levels after their stomachs were moderately full also had

greater activation of the left amygdala. " This indicates that ghrelin

may control the reaction of the amygdala to satiety signals sent by the

stomach, " said Wang.

This study was funded by the Office of Biological and

Environmental Research within the U.S. Department of Energy's Office of

Science, the National Institute on Drug Abuse (NIDA), the National

Institute of Diabetes and Digestive and Kidney Diseases, the Intramural

Research Program of the National Institute on Alcohol Abuse and

Alcoholism (NIAAA), and the General Clinical Research Center at

University Hospital Stony Brook. DOE has a long-standing interest in

research on brain chemistry gained through brain-imaging studies.

Brain-imaging techniques such as MRI are a direct outgrowth of DOE's

support of basic physics and chemistry research.

The current study is part of a major focus of research at

Brookhaven Lab on the neurobiology of eating disorders and obesity and

their treatment. Earlier studies at the Lab have:

* identified brain circuits that may cause the obese to overeat

* shown

that levels of dopamine receptors, which receive chemical messages of

well being and reward in the brain, are decreased in the brains of

obese individuals

* demonstrated that parts of the brain responsible for sensation in the tongue, mouth, and lips are more active in the obese

* revealed

that the mere sight and smell of favorite foods spikes levels of

dopamine in the brains of food-deprived people - just as it spikes this

pleasure chemical in the brains of those with drug addictions in

response to their drug of choice

----------------------------Article adapted by Medical News Today from original press release.