With many new year resolutions including weight loss, a recent study concerning body fat has grabbed people’s attention. We all know too much fat is a bad thing. Yet studies into different types of fat – which burn energy rather than store it – suggest that there might be new ways to tackle obesity.

White ‘bad’ fat, is the type of fat that stores calories, and excess amounts of it cause people to put on weight. It’s found in abundance in obese people.

Brown fat generates heat and burns calories and has been linked to helping control weight. Brown fat dwindles with age – it was believed to only be present in children until researchers in 2009 found that it’s also active in up to 7.5 per cent of adults.

But now a newer study* in the journal Cell has reported the discovery of beige fat – another type of fat present in “most or all human beings” which has the ability to both store and burn calories.

Beige – the new brown
The existence of beige fat cells was first suggested in 2008 by Dr Bruce Spiegelman, a cell biologist at Harvard Medical School. But it wasn’t until this recent study, conducted by Dr Spiegelman and scientists at Harvard’s Dana-Farber Cancer Institute, that it’s been possible to isolate the cells and determine their genetic profile.
Beige fat cells, the scientists say, can be found in humans in small deposits around the collarbone and spine. In this study, they cloned beige fat cells in mice to look at them more closely.

The scientists discovered that beige fat is similar to brown fat in some ways. Both contain iron, which gives them their distinct colour, and both have an abundance of mitochondria – a part of the cell which can produce heat and burn calories.

But there were also some significant differences. Brown fats cells give off high levels of UCP1 a protein that mitochondria need to produce heat and burn calories. In comparison, beige fact cells usually express low levels of UCP1. However, beige fat can be stimulated to produce a lot of UCP1 when exposed irisin, a hormone released by muscles during exercise or when muscles shiver due to exposure to cold temperatures.

It was also found that the cells differ from each other genetically. Brown fat cells originate from muscle stem cells. In contrast, beige fat cells emerge from white fat cells – making it possible for them to store fat when levels of UCP1 are low, but burn it when muscles release irisin through exercise.

Fighting obesity
The study reports: “The therapeutic potential of both kinds of brown [brown and beige] fat cells is clear, as genetic manipulations in mice that create more brown or beige fat have strong anti-obesity and anti-diabetic actions.”

It is hoped that these discoveries may lead to new treatments in obesity. Indeed, Spiegelman has already set up a biotech company, Ember Therapeutics, in an attempt to develop irisin in a drug form to stimulate brown and beige fat cells to increase weight loss.

However, this is still a very new field. While more brown and beige fat cells are found in fit compared to sedentary people, for example, more research is needed to prove the two are directly linked. It’s believed that the effects of irisin may only be temporary but scientists don’t know this for sure yet.

*Spiegelman, Bruce M et al. Beige Adipocytes Are a Distinct Type of Thermogenic Fat Cell in Mouse and Human. Cell, Volume 150, Issue 2, p366-376. July 2012