MRI Scans Reveal What Obesity Does to the Brains of Teens

Obesity has been linked to brain damage in teenagers, with scans revealing impairment in regions associated with emotions, cognitive function and appetite control.

Scientists, whose study is to be presented at the Radiological Society of North America (RSNA) next week, say the changes could be related to inflammation in the nervous system.

"Our maps showed a positive correlation between brain changes and hormones such as leptin and insulin," said study co-author Pamela Bertolazzi, a Ph.D. student and biomedical scientist at the University of São Paulo in Brazil, in a statement.

"Furthermore, we found a positive association with inflammatory markers, which leads us to believe in a process of neuroinflammation besides insulin and leptin resistance."

Bertolazzi and colleagues came to this conclusion after analyzing MRI scans of 59 obese adolescents and comparing the scans to those of 61 healthy adolescents, all aged 12 to 16 years old.

The researchers used a technique called diffusion tensor imaging (DTI). This enables scientists to monitor the distribution of water along the brain's signal-carrying white matter tracts as a direct measure of brain damage. Specifically, they used a measurement called fractional anisotropy (FA)—a reduction in FA directly positively correlates to greater damage of the white matter.

Model of Human Brain
A model of a human brain on display in the Calouste Gulbenkian Foundation in Lisbon, Portugal. Scans reveal damage to the brain's white matter in obese teenagers. Horacio Villalobos#Corbis/Corbis/Getty

In obese adolescents, the scans revealed lower FA values in areas of the brain related to emotional control and reward (the middle orbitofrontal gyrus) as well as the corpus callosum—a bundle of 200 million nerve fibers called axons that join one hemisphere of the brain to the other. Its job is to provide a bridge for information related to motor, sensory, and cognitive functions to pass from the left or right hemisphere to the other, and vice versa.

This damage correlated with higher levels of hormones such as leptin and insulin. The first is produced by the body's fat cells and is associated with the regulation of appetite and fat stores. Leptin resistance can cause people to keep eating even if the body has sufficient (or excessive) fat stores, and results in the production of more leptin. The second is produced in the pancreas and helps control blood sugar levels. Obesity can cause insulin resistance and thus, increase a person's risk of developing type 2 diabetes.

Bertolazzi says further research will need to show whether or not the inflammation is caused by structural changes in the brain, and determine whether or not the process can be reversed.

"In the future, we would like to repeat brain MRI in these adolescents after multi-professional treatment for weight loss to assess if the brain changes are reversible or not," she said.

The U.S. Centers for Disease Prevention and Control (CDC) calls childhood obesity "a serious problem." As of 2015-2016, 39.8 percent of U.S. adults and 18.5 percent of U.S. children met the criteria for obese. That includes 18.4 percent of children aged 6 to 11 and 20.6 percent of adolescents aged 12 to 19. This is more than three times the number of children and adolescents affected by obesity in the 1970s, the researchers say.

Brain Scans
Bertolazzi and co./RSNA