Brains of obese teens show damage in critical areas that control appetite, emotions and cognitive functions

The findings suggest the disease triggers inflammation in the nervous system that could damage important regions of the brain, say experts.


                            Brains of obese teens show damage in critical areas that control appetite, emotions and cognitive functions

The brains of obese children and teenagers are damaged in important regions that control appetite, emotions, and cognitive functions.

The findings, which suggest there may be a direct association between childhood obesity and brain development, are very concerning as obesity now affects 1 in 5 children and adolescents in the US, say experts.

The research team used MRI to compare the brains of obese and healthy weight adolescents and found visible signs of damage that may be related to inflammation in the brains of obese adolescents, which might make it harder for them to control their eating habits.

The scans also showed changes in a brain region related to emotional control and the reward circuit, which could also lead to excess eating, say experts. 

"Brain changes found in obese adolescents related to important regions responsible for the control of appetite, emotions and cognitive functions," says study co-author Dr Pamela Bertolazzi, a biomedical scientist and PhD student from the University of São Paulo in Brazil.

According to the researchers, while obesity is primarily associated with weight gain, the new evidence suggests that the disease triggers inflammation in the nervous system that could damage important regions of the brain.

The scans showed changes in a brain region related to emotional control and the reward circuit, which could also lead to excess eating, say experts. (Getty Images)

What do the numbers say?

Obesity in children and young people is a significant public health problem globally. According to the US Centers for Disease Control and Prevention (CDC), the percentage of children and adolescents affected by obesity has more than tripled since the 1970s in the US. For children and adolescents aged 2-19 years, the prevalence of obesity was 18.5% and affected about 13.7 million children and adolescents, shows national estimates from 2015–2016. 

"The prevalence of obesity was higher among youth aged 6–11 years (18.4%) and adolescents aged 12–19 years (20.6%) compared with children aged 2–5 years (13.9%)," says CDC

Globally, according to a study published in The Lancet, the number of obese children and adolescents increased tenfold — from 11 million in 1975 to 124 million in 2016. The study analyzed weight and height in nearly 130 million people, including 31.5 million children aged 5-19 years. 

The analysis

The aim of the current study was to investigate the influence of childhood obesity on changes in brain connectivity. The researchers used a technique in MRI called diffusion tensor imaging (DTI), which tracks the diffusion of water along the brain's signal-carrying white matter tracts, to study the damage directly.

They compared scans of 59 obese adolescents and 61 healthy adolescents, aged 12-16. From the imaging technique, the researchers analyzed 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 analysis shows that the obese group had significantly lower FA values in multiple white matter regions than those who had a healthy weight. 

"The results showed a reduction of FA values in the obese adolescents in regions located in the corpus callosum, a bundle of nerve fibers that connects the left and right hemispheres of the brain. A decrease of FA 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 FA," says the study.

The findings will be presented at the annual meeting of the Radiological Society of North America (RSNA) next week (December 1 to 6).

Reduction in fractional anisotropy (FA) in obese patients compared to the control group: At the intersection of the alignment vectors, a large cluster of FA decrease located in the corpus callosum on the left. In red: Reduction of FA in obese patients compared to controls. A reduction in FA is indicative of increasing damage in the white matter. (Study author and RSNA)

According to the researchers, the pattern of damage correlated with some 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.

The 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.

"Our maps showed a positive correlation between brain changes and hormones such as leptin and insulin. We also found a positive association with inflammatory markers, which leads us to believe in a process of neuroinflammation besides insulin and leptin resistance," says Dr Bertolazzi. 

The researchers say further studies are needed to determine if this inflammation in young people with obesity is a consequence of structural changes in the brain.

"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," says Dr Bertolazzi.

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