The human body contains small amounts of a calorie burning tissue called brown fat (brown adipose tissue, BAT) that converts food energy directly into heat. White fat does the opposite— it stores energy. BAT is an important heat generating tissue in hibernating animals. It promotes non-shivering thermogenesis, which generates heat and helps animals and humans adapt to the cold. Individual differences in BAT content and activity plays an important role in human obesity. BAT is turned on by the sympathetic nervous system, which is the body’s fight-or-flight system for coping with stress and emergencies. However, a recent study by Piryank Motiani from Turku University in Finland and colleagues found that exercise, an important activator of the sympathetic nervous system, was not a significant stimulus for brown fat activation in middle-aged men. Increasing brown fat activation helps people expend more calories and burn more fat. Cold exposure and key nutrients, such as L-arginine, L-citrulline, and L-glutamate can increase brown fat activity, which increases caloric expenditure and promotes fat burning.

(Diabetes, Obesity and Metabolism, published online March 20, 2018)