Editors' ChoiceObesity

BAT Burns Fat? Cool.

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Science Translational Medicine  11 Sep 2013:
Vol. 5, Issue 202, pp. 202ec148
DOI: 10.1126/scitranslmed.3007485

In modern times, we turn up the thermostat if we’re cold, but evolution designed our bodies to acclimate to cold temperatures and maintain euthermia (normal body temperature) without the assistance of external climate control. One way mammals thermoregulate is through the burning of calories by brown adipose tissue (BAT), whose main function is thermogenesis. Until recently, BAT was believed to be present mainly in rodents and animals that hibernate, whereas in humans its presences in newborns was thought to dissipate by adulthood. But 4 years ago, functional BAT was identified in adult humans, leading to a barrage of research investigating how to harness BAT’s calorie-burning power to combat obesity. Now, two studies examine whether cold exposure activates brown fat in adult humans and thereby increases energy expenditure.

In the first study, van der Lans et al. exposed 17 healthy, lean [mean body mass index (BMI) = 21.6kg/m2], young (mean age 23) men and women to 15 to 16°C (59 to 60.8°F) for 6 hours per day on 10 consecutive days. Fluorodeoxyglucose-positron emissions tomography/computed tomography (FDG-PET/CT) imaging of the subjects revealed that cold exposure and acclimation significantly increased BAT activation, nonshivering thermogenesis, and energy expenditure. The authors suggest that intermittent, daily cold exposure may be a possible therapy for obesity by its effect on increasing energy expenditure. In the second study, Yoneshiro et al. randomized 22 lean, healthy, young men whom they had characterized as having low or undetectable BAT activity into two groups: One group was exposed to 17°C (62.6°F) for 2 hours per day for 6 weeks (n = 12 participants) and a control group lived a “normal life style” for the same period of time (n = 10 participants). The authors found that compared with the control group, the cold-exposure group had increased BAT activity, increased energy expenditure, and, importantly, decreased fat mass.

These studies provide insight into using cold exposure to harness the power of BAT to promote thermogenesis, increase energy expenditure, and “burn” fat. Because these studies were conducted in lean individuals and were relatively short in duration, the experiments need to be conducted in obese humans over longer periods of time to assess both efficacy and feasibility of such interventions. Concurrently, researchers are also attempting to discover and develop pharmaceutical agents that activate BAT. In the meantime, regular dips in a cold swimming pool might help us burn a few extra calories.

A. A. J. J. van der Lans et al., Cold acclimation recruits human brown fat and increases nonshivering thermogenesis. J. Clin. Invest. 123, 3395–3403 (2013). [Full Text]

T. Yoneshiro et al., Recruited brown adipose tissue as an antiobesity agent in humans. J. Clin. Invest. 123, 3404–3408 (2013).[Full Text]

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