Whether it turns up unexpectedly around our waists, as cellulite on our thighs or as deposits in our arteries, fat is rarely welcome. In the UK 60% of the population is carrying too much fat and many spend huge amounts of money trying to get rid of it. The fat cell is clearly not wanted. But recent research tells us that not all fat cells are the same and that, bizarrely, some may even be helpful in losing weight.
There are two types of body fat (adipose tissue) – white and brown. White fat is the depressingly familiar type, hanging over the belt or covering the thighs and upper arms etc. In overweight humans, white fat may account for 40% or more of total body weight. Brown adipose tissue (BAT), on the other hand, is stored in small amounts around the neck area and is involved in burning calories rather than storing them. The main function of BAT is to maintain body temperature. When the external temperature falls, BAT stores are activated and burn energy to form heat.
Whilst it has long been known that newborn babies – as with many small mammals – have active BAT, it has always been assumed that once we reach adulthood, our BAT stores became inactive. But recent research has shown that adult humans have BAT stores which are capable of burning significant amounts of energy. In one study, a typical individual carried 63 grams of brown fat, enough to burn in a year the amount of energy stored in about 4 kilograms (almost nine pounds) of white fat! Overall, BAT could burn up to 20% of an average person’s daily calorie intake, so making it an exciting target for the weight loss drugs of the near future.
But there is another twist to this fascinating story which could also shed some light on the causes of obesity. A naturally occurring hormone called melatonin seems to increase the activity of BAT stores. Unfortunately, modern artificial lighting dramatically reduces melatonin production in the body, so that the calorie-burning activities of BAT tissue are effectively switched off.
So, if the BAT hypothesis is right, an effective piece of weight loss advice would be to turn off the heating and the lights – what you get up to in the dark is for you to decide!
Dr David Ashton
19th September 2011
