Briefs: Losing weight thanks to cooling?
Could cold temperatures become a way to lose weight? Three recent studies underline the role of brown adipose tissue (BAT) in burning fat to produce heat and regulate body temperature. Human adults were previously thought to be lacking BAT. All three studies used tomography, a medical imaging technique that measures the absorption of 18F-fluorodeoxyglucose (FDG), a harmless form of glucose into various tissues, thus giving indications on the metabolic activity of each tissue. In small mammals, exposure to cold stimulates the release of the hormone adrenaline which triggers brown fat cells to consume more fat and glucose for heat production. The experiments involved for example volunteers to stay in rooms at 17-19°C, or to immerse one foot in cold water for 5 minutes every five minutes. In all individuals, exposure to cold led to a 15-fold increase in FDG uptake in the supraclavicular region. Biopsy of this region in three volunteers revealed the presence of BAT. Up to 63 g of supraclavicular BAT was found in one individual, a mass estimated as able to burn the equivalent amount of energy during a year as is stored in about 4 kg of white fat tissue. BAT activity also showed a significant negative correlation with percentage body fat and correlated positively with resting metabolic rate. Cold temperatures activate BAT in adult humans, apparently more often in women than men? Could a good way for people with metabolically active BAT to lose weight simply be to turn the cooling down? Drugs that mimic the action of cold by activating the sympathetic nervous system are also being considered.