A study using PET scans of children found brown adipose tissue (BAT) -- a kind of fat that burns energy -- is more active in thinner kids.

The study, published online Friday in the Journal of Pediatrics, found that children with a lower body-mass index tended to have more brown fat activity, as determined by (18)F-fluorodeoxyglucose PET scans. The experiment involved 385 scans of 172 children, aged 5-21, at Children's Hospital Boston.

"BAT activity increases from childhood into adolescence, when it is detected in almost half of patients, and it correlates inversely with obesity, suggesting that BAT may play a prominent role in pediatric metabolism," write the researchers. The senior author was Dr. Aaron M. Cypress, with Beth Deaconess Medical Center and Joslin Diabetes Center in Boston.
The function of brown fat is to burn calories to make you warmer. It's especially prevalent in newborns, who can't shiver to heat up.

Earlier studies have shown, in both mice and humans, the brown fat becomes more active in colder temperatures. These findings even led some researchers to speculate in a January Obesity Reviews article that modern warmer indoor temperatures over the winter -- due to freer use of heating systems -- could be linked to obesity.

But surprisingly, in this study, brown fat prevalence in children was not linked to outdoor temperature.

Also, the study didn't determine a causal relationship between brown fat and body size: that is, it's not clear if brown fat activity helps kids stay thinner, or if someone being thin causes the tissue to be more prevalent or active.

“That’s the billion dollar question,” Cypress said in a statement.

According to the paper, brown fat activity peaks between 13-15 years. Although it was thought BAT mostly vanished in adulthood, previous work by Cypress' team found BAT was active in around 3 to 7.5 percent of adults.

More Industry Headlines