Brown fat (brown adipose tissue) is one of the two types of fat (the other is white fat) found in the body. Brown adipose tissue (BAT) is a specialized tissue whose function is to produce heat; it is found in the upper back, on the side of the neck, between the collar bone and the shoulder and along the spine, all in very small amounts. BAT is more prevalent in slim people rather than obese people and the young have more than the old. It is metabolically highly active opposed to white fat, which is the bodies stored fat and has a low rate of metabolic activity. Over time various studies on rodents showed that as the rodents could not shiver, BAT was vital for proper thermogenesis during cold exposure; so in order to generate any heat, their bodies relied upon this brown fat. Human infants also use brown fat the same way rodents do, but until recently we didn’t know for sure whether it contributed to cold-induced non-shivering thermogenesis in adult humans. So up until 3 years ago scientists didn’t think human adults had any brown fat; since adults can shiver and it is this process that allows the body’s temperature to be raised when we are cold.
In a new study scientists found that one form of BAT is activated when people get cold; this activation results in the BAT cells ‘sucking’ the fat out of the rest of the body when they run out of their own repositories. Dr Andre Carpentier of the University of Sherbrook, Quebec, Canada says – “We have proof that this tissue burns calories — yes, indeed it does, but what happens over the long term is unknown.” In the study, the subjects (all men) were kept chilled but not to the point of shivering which itself burns calories. Their metabolic rates increased by 80%, all from the actions of a few ounces of cells. The brown fat also kept its subjects warm. The more brown fat a man had, the colder he could get before he started to shiver. The brown fat burned an average of 250 calories over 3 hours.
In another study scientists discovered a form of brown fat that can be created from ordinary white fat via exercise. This type of BAT is interspersed in the white fat and is much harder to study and doesn’t appear in large amounts either. Rodent studies show that through exercise white fat converts to brown fat and that this is possible as the hormone irisin (newly discovered) converts the white fat cells into brown fat cells and these cells burn calories. This rings true for the human study as well; we also have irisin in the blood, which is identical to the irisin in rodents (mice). The recent discovery in relation to BAT and exercise may well explain to some extent, the relationship between the amount of calories required to perform an exercise and the actual calories burned during the exercise; calories burned during exercise may exceed calories required to perform the exercise. The excess calories burned may be a result of some of the white fat cells turning brown.
Dr Carpentier says “There is still a lot of research to do before this strategy can be exploited clinically and safely” Unfortunately scientists can’t yet ‘turn on’ the brown fat in people without putting them in cold rooms or subjecting them to pretty much 24-7 hour workouts, if they could then we would have one amazing weight loss treatment!