Brown fat may be key to metabolically healthy obesity

Researchers from the Medical University of Vienna (MedUni Vienna) and Vienna General Hospital have shown that people who are seriously overweight who also have active brown fat have a healthier metabolism and use more energy than obese people without brown fat. The team’s findings, published in the journal Diabetes, suggest that the presence of brown fat may protect against secondary obesity-related diseases.

For years now, medical researchers have been trying to understand why some obese people are less likely to develop health conditions such as diabetes or high blood pressure than others of similar weight. It now seems that an important factor in what is known as ‘metabolically healthy obesity’ has been identified in the form of brown fat.

“Brown fat has long been thought to benefit metabolism because, unlike the much more common white storage fat, it can burn energy in the form of heat,” said Florian Kiefer, Head of the MedUni Vienna research group. “Babies and toddlers in particular use brown adipose tissue to maintain their body temperature, but the proportion of brown fat in the body decreases with age and with excess weight.”

In the recently published study, the Viennese research group discovered that more than a third of severely overweight adults (BMI >35 kg/m²) still have active brown fat. In the study, the volunteers were first exposed to moderate cold using cooling vests to activate brown fat, which was then detected by PET-CT scanning.

“In adults, brown fat is predominantly found at the base of the neck and in the rib cage,” Kiefer said. “A brief period of cold stimulation of about one hour is sufficient to activate it.”

The overweight participants with brown fat displayed higher energy consumption, less harmful abdominal fat, healthier sugar metabolism and fewer signs of fatty liver disease than a control group of similar weight with no detectable brown fat. Kiefer said it was “quite amazing that the participants with brown fat did better on almost all metabolic parameters, even though they had a slightly higher BMI”, with the results indicating that it’s “not just the quantity of adipose tissue that matters, but more importantly its quality”.

In fact, differences in fat distribution may have contributed to the advantageous metabolic status. In particular, the proportion of deep-lying abdominal fat (visceral fat), which represents a high risk for diabetes and heart attack, was significantly lower in the brown fat group.

“It is conceivable that the increased metabolic activity of brown fat will preferentially break down and burn harmful visceral fat stores first,” Kiefer said. “That is why we are currently working hard to develop drug treatments to activate brown fat.”

Image credit: ©stock.adobe.com/au/New Africa

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