A striking new study, presented at the annual meeting of the Radiological Society of North America, claims to have identified white matter brain damage in obese teenagers. The researchers did not find the same brain changes in non-obese subjects, and suggest the structural differences correlate with metabolic markers that point to obesity as a causal factor.
The new study imaged the brains of 120 teenage subjects, half of which were classified as obese. Using an MRI technique known as diffusion tensor imaging (DTI) the researchers calculated a measure called fractional anisotropy (FA), an effective metric that indicates connectivity across the brain’s white matter. The lower the FA value, the more likely there is some kind of white matter brain damage.
Compared to the healthy control cohort, the researchers saw low FA values in several brain regions among the obese subjects. Low FA values were identified in the corpus callosum, a region connecting the left and right sides of the brain, and the middle orbitofrontal gyrus, a brain region strongly related to appetite, emotional control and reward behavior.
"Brain changes found in obese adolescents related to important regions responsible for control of appetite, emotions and cognitive functions," says Pamela Bertolazzi, co-author on the new study from the University of São Paulo in Brazil.
In an effort to affirm a link between the brain changes and obesity, the researchers took blood samples from all subjects. Several obesity-related inflammatory markers could be distinctly correlated with the brain changes, including leptin, insulin and proteins from the tumor necrosis factor (TNF) family.
"Our maps showed a positive correlation between brain changes and hormones such as leptin and insulin," says Bertolazzi. "Furthermore, we found a positive association with inflammatory markers, which leads us to believe in a process of neuroinflammation besides insulin and leptin resistance."
It is difficult to conclude any kind of causality from this early imaging study, and even then, it's harder to confirm the direction of causation. Do these brain changes precede obesity, or are they the downstream result of obesity?
The new research, which is yet to be published in a peer-reviewed journal, is not an anomalous outlier. A recent study from the University of Cambridge also detected distinct structural differences in the brains of obese children, compared to a healthy control group. The Cambridge researchers were cautious about hypothesizing what their study could mean, and were hesitant to discuss what may come first, the obesity or the brain damage.
A study from the University of Glasgow earlier this year suggested there may be a direct causative link between high-fat diets and depression, following a long-observed correlation between obesity and depression. The Glasgow research focused on animal experiments, elucidating how dietary fats can enter the bloodstream, travel to the brain, accumulate in a specific region, and ultimately induce depression-like symptoms.
The implication of the Glasgow research is that depression doesn’t cause obesity, but instead, obesity can directly cause depression. Adding these newer brain imaging studies into the mix and a reasonable hypothesis emerges suggesting high-fat diets leading to obesity can explicitly effect the brain in ways that influence emotional control and mental health.
It’s still early days for this kind of research and plenty more work is needed to better tease out these new observations linking obesity with structural brain changes. One of the big questions Bertolazzi and her team hope to answer in the next stage of their research is whether these obesity-related brain changes are reversible through weight-loss methods.
The new study will be presented at the upcoming annual meeting of the Radiological Society of North America.
