Brown fat is a beneficial type of fat that burns energy and glucose to make heat, and animal studies have shown that it protects against diabetes and obesity. Now, new research suggests long-term exposure to cold environments can stimulate growth of this "good" fat in humans, potentially benefitting glucose and energy metabolism.
Results of the study were presented at the joint meeting of the International Society of Endocrinology and the Endocrine Society in Chicago, IL, over the weekend. They are also published in the journal Diabetes.
Dr. Paul Lee, former research fellow at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) of the National Institutes of Health (NIH), led the study.
In previous research, he and his colleagues have shown that people with abundant brown fat stores tend to be lean and have low blood sugar levels, and they even showed that ordinary white fat cells can transform into the beneficial brown fat cells.
However, until now, how brown fat is regulated in humans and its relationship with metabolism has been unclear.
To further investigate, Dr. Lee and his team analyzed the impact of controlled temperature acclimatization on brown fat - also known as brown adipose tissue (BAT) - and energy balance.
Their research, called the Impact of Chronic Cold Exposure in Humans (ICEMAN) study, involved following five 19-23-year-old men for a period of 4 months.
Cold increased brown fat, while warmth suppressed it
Though the study participants took part in their normal daytime activities, they slept in a private room, where the air temperature varied.
The new study suggests exposure to mild, colder temperatures stimulates "good" brown fat, while exposure to warmer temperatures suppresses it.
During the first month, the rooms were set at 24º C, which the researchers describe as a "thermo-neutral" temperature at which the body does not need to work to either produce or lose heat.
For the second month, the temperature was moved down to 19º C, then back to 24º for the third month. For the final month, the temperature was moved up to 27º C.
All throughout this period, the researchers measured the men's brown fat using cold-stimulated PET/CT scans, and they measured tissue metabolic changes with muscle and fat biopsies.
Results showed that the mild cold (at 19º C) increased the men's brown fat amount and activity by about 30-40%, while the mild warmth (at 27º C) decreased the amount of brown fat to below that of baseline.
Furthermore, Dr. Lee notes that the increases in brown fat were "accompanied by improvement in insulin sensitivity and energy burning rate after food."
Commenting on their findings, Dr. Lee adds:
"The improvement in insulin sensitivity accompanying brown fat gain may open new avenues in the treatment of impaired glucose metabolism in the future. On the other hand, the reduction in mild cold exposure from widespread central heating in contemporary society may impair brown fat function and may be a hidden contributor to obesity and metabolic disorders."
Warmer houses 'could be contributing to obesity'
The study authors say their findings lead them to hypothesize that manipulating temperature in order to grow brown fat could be a promising strategy in obesity and diabetes treatment.
Dr. Lee notes that studies in both the UK and US measuring household temperatures in individual homes during the last few decades have shown that the temperature has climbed from around 19º C to around 22º C, which is "a range sufficient to quieten down brown fat."
"So in addition to unhealthy diet and physical inactivity, it is tempting to speculate that the subtle shift in temperature exposure could be a contributing factor to the rise in obesity," he concludes.
Earlier this year, Medical News Today reported on a study that suggested shivering is as good as exercise for producing brown fat.