Reduced Brain Impact of Eating in Obesity
Countless studies now show that there are important metabolic differences between people living with obesity and those living with normal weight.
Of particular interest are studies showing difference in hormonal and neuronal response to eating.
Now, a study by Nancy Puzziferri and colleagues from the University of Texas, published in OBESITY, show that the brain response to eating may differ substantially between people with normal weight and those living with obesity.
The study was conducted in 15 women with severe obesity and 15 age-matched lean women (18-65 years old).
When fasting, brain perfusion measured by arterial spin labeling was similar between obese and normal-weight volunteers and both groups showed significantly increased activity in the neo- and limbic cortices and midbrain activity in functional magnetic resonance imaging (fMRI).
However, after a standard meal, the lean group showed significantly decreased activation in these areas, whereas the group with severe obesity showed no such decreases.
In line with these findings, after eating, subjective appeal ratings of food decreased in lean but not in the obese women.
As the researchers note, these findings are in line with previous brain imaging studies.
“…after eating, participants with severe obesity maintain activation in the midbrain, one of the most potent reward centers. Thus, once satiated after eating, participants with severe obesity continue to perceive food as appealing and their brains continue to be activated by visual food cues as though they were hungry.”
These finding would explain why individuals with obesity are perhaps at a far greater risk to continue eating (especially highly-palatable foods such as dessert) even when satiated.
What these type of studies do not tell us whether these differences are primary (i.e. could have led to the weight gain in the first place) or secondary (i.e. the consequence of weight gain).
Be that as it may, the findings do show that there are significant differences in how the brain responds to eating between people with obesity and those with normal weight.
Clearly, the next step would be to see if this lack of response can be restored through weight loss (e.g. bariatric surgery) or through anti-obesity medication.
At least the findings perhaps explain why simply telling people with an activated limbic system to “push away from the table” may not be all that effective.