Obese teenagers can have certain brain differences from their thinner peers -- changes that might signal damage from inflammation, a new, preliminary study suggests.
Using advanced MRI techniques, researchers found that obese teenagers tended to have signs of decreased "integrity" in the brain's white matter. White matter contains the fibers that connect different areas of the brain. In this case, lower white-matter integrity was seen in a brain region related to emotional control and "reward" seeking.
The findings, based on 120 teenagers, are considered preliminary. Experts said it's not clear what they might mean.
But the findings add to evidence linking obesity to certain brain structure differences. Recent studies of middle-aged adults, for example, have found evidence of brain tissue "shrinkage" among those with high levels of body fat -- particularly around the belly.
One possibility is that excess amounts of body fat directly harm the brain through inflammation, the researchers suggested.
In the new study, there was a correlation between decreases in white matter integrity and higher levels of certain inflammatory substances in the blood. Teens with those brain changes also tended to have higher levels of the hormones leptin and insulin. Leptin is involved in appetite control, while insulin regulates blood sugar levels.
Dr. Harold Bays is a fellow of the Obesity Medicine Association and medical director of the Louisville Metabolic and Atherosclerosis Research Center, in Kentucky.
Bays said brain-imaging studies like these provide additional objective evidence that obesity is not just a matter of "willpower."
"Some people don't see obesity as a disease and argue that it's all about behavior," said Bays, who was not involved in the study.
But, he said, obesity is actually driven by a range of underlying factors. "Yes, behavior is a key component," Bays said. "But there are other components, too, including a neurological one."
So does extra body fat cause the brain differences? Or do the brain differences feed weight gain?
Bays suspects there may be a two-way street -- where, for example, brain differences contribute to obesity, and obesity ramps up inflammation that affects the brain.
But this study does not get at that question.
"This doesn't tell you anything about the direction of the relationship," said Allan Geliebter, a senior scientist in psychiatry at Mount Sinai's Icahn School of Medicine in New York City.