The body fat that's good for you

CRACK this riddle... What am I? The more of me you have, the less you weigh. The older you get, the quicker I disappear.

fat

CRACK this riddle... What am I? The more of me you have, the less you weigh. The older you get, the quicker I disappear.

Men don't have as much of me as women do. Until recently, scientists didn't think adults had any of me at all and believed I could only be found in rodents and newborn babies.

The answer is: brown fat, a beneficial part of our bodies that researchers are now unlocking some of the mysteries of.

While most body fat - white fat - can be harmful, researchers believe brown fat may hold a key to fighting obesity in the future.

What is brown fat?

Dr Paul Lee, an endocrinologist at the Garvan Institute of Medical Research in Sydney, who is now continuing his research at the National Institutes of Health in Washington DC, explains:

"Think of white fat as an energy storehouse and brown fat as a generator. Brown fat burns fat, rather than storing it. As it burns fat, it turns this energy into heat to keep us warm."

Brown fat is present in newborn babies to help them maintain body heat, but scientists believed that it disappeared after infancy.

However, new imaging technology has revealed that people actually retain varying levels of brown fat in adulthood - usually around the neck, shoulders, spine and adrenal glands.

More fat the better

Lee's research has found that people with higher reserves of brown fat are usually slimmer, have a lower body mass index and a healthier blood glucose level.

"It looks as if people who are overweight have less brown fat," he says.

"Now we're looking into whether having less brown fat means burning less fat in general and thus putting on weight. Or is it perhaps because a person is overweight and has the layer of fat that provides sufficient insulation that their brown fat atrophies because there's no longer the need for it?"

While 50 grams of white fat stores around 300 kilocalories of energy - potentially leading to weight gain - the same amount of brown fat burns 300 kilocalories a day, which is why it has a lot more health benefits.

Activating brown fat

Scientists at Boston's Dana-Farber Cancer Institute have found that exercise may convert some white fat into brown by increasing the level of the hormone irisin.

It appears to "activate" the genes that transform one type of fat into another. These researchers are now developing an irisin-based drug to aid weight loss and also improve blood glucose levels, reducing the risk of diabetes.

Professor Peter Clifton, head of nutrition at the Baker IDI Heart and Diabetes Institute in Melbourne, agrees that working out increases brown fat efficiency.

"If you exercise, you can activate brown fat, although we don't yet know how much training you have to do. That said, regular exercise and increasing muscle helps the effectiveness of brown fat," he says.

Kickstart in the cold

Staying cool also seems to stimulate brown fat. In a study at the University of Sherbrooke in Quebec, a group of men were placed in a cool room - chilled but not cold enough to make them shiver - and their metabolic rates increased by 80 per cent as their brown fat kicked into action.

"Studies have shown that even exposure to mild cold - 18ºC or 19ºC - will activate brown fat," Lee adds.

"One hypothesis is that obesity is reaching epidemic proportions because we're eating more and are less active, but we are also no longer exposed to the cold as much. Everywhere is so thermally regulated that we're not allowing brown fat to grow as a response to feeling chilly."

The fat of the future

As we learn more about the nature of brown fat, its potential medical benefits become increasingly apparent, too. Lee and his team at the Garvan Institute have shown that brown fat can be cultured from adult stem cells.

This raises the possibility that it could eventually be grown outside the body and then transplanted into humans. Alternatively, the production of brown fat may eventually be stimulated with drugs.

"We know almost all humans have some brown fat. Some have more, some have less, but it's there," Dr Lee says.

"If we can get the conditions right, we can potentially stimulate the growth of it in humans. Or we could harvest the human brown fat cells, grow them in a laboratory, then put them back into the body to increase the amount.

Knowing brown fat exists may help us discover if there are additional measures we can use to help people enjoy a more healthy weight."

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