When Stomach Speaks But Brain Won’t Listen

At the Brookhaven National Lab scientists used functional MRI to detect the effect a satisfied stomach had on a hungry brain. Using a number of subjects, the researchers noted that overweight people have a far weaker response in the brain to signals from a full stomach.

“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.

Press release: Overweight People May Not Know When They’ve Had Enough