Is your fat brown, beige or white?

For a long time the only fat we ever heard about was white. It was the repository of excess energy and was displayed as the lumpy bits when our BMI was high. But now some new colours of fat are coming forward and, like in Animal Farm, it seems that not all fats are created equal.

Professor Jan Nedergaard from the University of Stockholm addressed the International Union of Nutritional Sciences (IUNS) 20th International Congress of Nutrition yesterday and the topic of his plenary session was the potential of brown fat - New powers of brown fat: Fighting the metabolic syndrome.

Until recently, brown fat was only of passing interest, but new research has shown it to be a major promoter of energy expenditure, with a consequent role in the metabolism of triglycerides and glucose.

Brown fat is used by young children to maintain a good body temperature in the cold. However, an increasing number of studies suggest that adults have small amounts of this brown fat, which could help improve their metabolism and thus prevent obesity.

Half fat, half muscle, brown fat looks more like muscle. “Indeed, it has been shown that young cells can differentiate into both muscle and brown fat but not into normal fat,” explained Professor Jan Nedergaard of the Department of Molecular Biosciences at The Wenner-Gren Institute, Stockholm (Sweden). As children get older their brown fat becomes muscle.

To produce thermogenesis, brown fat uses triglycerides and glucose in the bloodstream. “All published studies show the major capacity of brown fat to take up and assimilate blood glucose, making it a weapon for use against diabetes. It has also been shown that brown fat can burn extra energy if ingested with food. What is not known yet is how important it is and how it can be regulated,” pointed out Professor Nedergaard.

Although there are many ongoing studies, the main obstacle to find out the whole potential of brown fat is that “we still have no way of modifying the amount of this type of fat in humans, by using a drug, for example”, he indicated.

What appears to have been shown is that obese people have less of this brown fat than people with normal weight. “We don’t know, however, whether this low amount of brown fat (partly) explains why (some) people become obese. But in experimental animals, a lower activity of brown fat is sufficient to cause obesity,” explained Professor Nedergaard.

And the last part of the fat puzzle is a recent discovery, ‘brite’ or ‘beige’ fat. “These are normal fat cells that acquire properties of brown fat cells, including the capacity to burn excess energy, although to a smaller extent than brown fat.” The importance of this ‘new arrival’ is still under ‘investigation and discussion’.

The 20th International Congress of Nutrition, currently underway in Granada, is promoted by the IUNS and organised by the Spanish Nutrition Society in conjunction with the Iberoamerican Nutrition Foundation and the University of Granada.