A decrease was also found in the middle orbitofrontal gyrus, an area related to emotional control and the reward circuit.
And there was a relationship between the pattern of damage and inflammatory markers like leptin, a hormone made by fat cells that helps regulate energy levels and fat stores.
In some obese people, the brain does not 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, a state in which the body is resistant to the effects of the hormone.
Dr Bertolazzi said: “Our maps showed a positive correlation between brain changes and hormones such as leptin and insulin.
“Furthermore, we found a positive association with inflammatory markers, which leads us to believe in a process of neuro-inflammation besides insulin and leptin resistance.”
She called for more studies to establish if this inflammation in young obese people is a consequence of the structural changes in the brain.
The researcher added: “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.”