While obesity is primarily associated with weight gain, a new study suggests it triggers inflammation in the nervous system that could damage important regions of the brain.
Developments in MRI, like diffusion tensor imaging (DTI), a technique that tracks the diffusion of water along the brain's signal-carrying white matter tracts, have enabled researchers to study this damage directly.
"Brain changes were found in obese adolescents related to regions responsible for control of appetite, emotions and cognitive functions," said study co-author Pamela Bertolazzi from the University of Sao Paulo in Brazil.
The World Health Organisation (WTO) data indicates the number of overweight or obese infants and young children increased from 32 million in 1990 to 41 million in 2016 globally.
For the study, researchers compared DTI results in 59 obese and 61 healthy adolescents, aged 12-16 years.
From DTI, the researchers derived a measure called fractional anisotropy (FA), which correlates with the condition of the brain's white matter. A reduction in fractional anisotropy is indicative of increasing damage in the white matter.
The results showed reduction of FA values in the obese adolescents in regions located in the corpus callosum, a bundle of nerve fibre that connects the left and right hemispheres of the brain.
Decrease of fractional anisotropy was also found in the middle orbitofrontal gyrus, a brain region related to emotional control and the reward circuit. None of the brain regions in obese patients had increased fractional anisotropy.
According to researchers, this pattern of damage correlated with some inflammatory markers, like leptin, a hormone made by fat cells that helps regulate energy and fat stores.
In some obese people, the brain doesn't respond to leptin, causing them to keep eating despite adequate or excessive fat stores. This condition, known as leptin resistance, makes the fat cells produce even more leptin.
Worsening condition of the white matter was also associated with levels of insulin, a hormone produced in the pancreas that helps regulate blood sugar levels. Obese people often suffer from insulin resistance.
"Our maps showed a positive correlation between brain changes and hormones, such as leptin and insulin," Bertolazzi said.
"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," she said.
The study will be presented at the annual meeting of the Radiological Society of North America (RSNA), scheduled from December 1 to 6 in the USA.