Obese people cannot convert 'white fat' to calorie-burning 'beige fat'

A new study has revealed that exposure to cold temperatures can convert white fat tissue from the thighs and belly to beige fat that burns calories for heat, but this biological response is hampered in obese people.

While white fat can burn calories when it takes on some characteristics from brown fat tissue, the tissue created in this process is called beige fat. When rodents are exposed to cold temperatures, they can convert white fat deposits to beige fat.

The researchers investigated whether human adults had the ability to transform some white fat deposits into beige fat when they were exposed to cold, and said study's authors, Philip A. Kern, MD, of the University of Kentucky School of Medicine in Lexington, KY said that browning fat tissue could be an excellent defense against obesity. It would result in the body burning extra calories rather than converting them into additional fat tissue.

Researchers analyzed belly fat tissue samples from 55 people to see if the tissue samples taken in winter showed more evidence of browning activity than those taken in summer.

Scientists also took thigh fat tissue samples from 16 people after they held an ice pack on the skin for 30 minutes. The analysis checked the tissue samples for specific genetic markers found in brown or beige fat.

Researchers analyzed the belly fat samples to see if there was a difference in response among lean and obese people. The analysis revealed that the seasonal effect of fat browning was blunted in obese people. Obesity was defined as having a body mass index greater than 30 and that inflammation can hinder the conversion of white to beige fat.

The study was published in the Endocrine Society's Journal of Clinical Endocrinology and Metabolism.