Brown Fat & Weight Control ?
     Newborns and hibernating animals have brown adipose tissue which is important in the thermoregulation and possibly body weight. Its primary function is to generate body heat due to a presence of large number of mitochondria and more capillaries than white fact requiring a greater need for oxygen and aerobic metabolism.
     Human individual variation in adaptive thermogenesis may be attributed to variations in the amount or activity of brown adipose tissue. Until recently, the presence of brown adipose tissue was thought to be relevant only in small mammals, hibernaters, and infants, with negligible physiologic relevance in adult humans.
   W.D.M. Lichtenbelt of Maastricht University, Netherlands N. Engl. J Med. 2009;360:1500-8) examined the presence, distribution, and activity of brown adipose tissue in lean and obese men during exposure to cold temperature and energy metabolism. They studied 10 lean healthy men — and 14 overweight or obese men under thermoneutral conditions (22°C) and during mild cold exposure (16°C). Brown-adipose-tissue activity was determined using 18F-fluorodeoxyglucose positron-emission tomography and computed tomography.
     Brown-adipose-tissue activity was seen in 23 of the 24 subjects (96%) during cold exposure* but not under thermoneutral conditions. The activity was significantly lower in the overweight or obese subjects than in the lean subjects. Resting metabolic rate had a significant positive correlation* with brown fat.
     Conclusion: Brown adipose tissue is high in humans, but its activity is reduced in men who are overweight or obese. Brown fat may be metabolically important in men, and because it is reduced yet present in most overweight subjects may make it a target for the treatment of obesity.   back