There have been hyped reports of late about “brown fat”. Different from the fat we mostly have (white fat), brown fat is capable of burning more energy. So the theory goes: if we have more brown fat, we can lose weight. But selective reporting and misinformation has blurred the lines between fact and fiction.
What is brown fat?
Grab that roll of fat on your stomach – that is white fat. The job of white fat is mainly to store energy, and then release it when other organs need it. We have much less brown fat which is hidden deep in the torso and neck. The main role of brown fat is to heat our body when we’re cold. To produce heat, brown fat cells expend (burn) energy.
Decades of research, mainly in rats and mice, tell us when brown fat is “activated” from its resting state (for example, by cold exposure) it can burn a lot of energy relative to its small size. The potential for health lies in whether this energy-burning power can be harnessed to treat obesity.
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Brown fat’s presence in adult humans has been known for decades. While previously believed to have no function, in 2009 a series of studies showed it does burn energy when activated by short-term (minutes/hours) cold exposure. Our brown fat can’t burn as much energy as the brown fat in mice, and some evidence suggests its normal energy burning level is so low as to be irrelevant.
When brown fat is not “activated”, its energy expenditure is very low. The level of cold exposure and the amount of the skin surface exposed control the amount of energy expenditure. Most importantly, “training” brown fat forces it to become better at burning energy. But training involves weeks of daily cold exposure for several hours – something we modern humans rarely, or ever, do.
Can cold showers activate brown fat?
This new awareness of brown fat has, unsurprisingly, led to exaggeration of its purpose, function and benefits in humans. Cold exposure as a health fad has boosted this recent popularity. Common recommendations to activate brown fat are cold showers and (worryingly), immersion for short periods in very cold (below -100°C) nitrogen gas.
Brown fat, like muscle, follows a “use-it-or-lose-it” principle and, as highlighted above, the more you use it the better it gets. Training brown fat requires cold exposure for several hours per day. So brief periods such as a few minutes in the shower or a dip in nitrogen gas interspersed in an otherwise warm lifestyle are unlikely to train brown fat in a meaningful way.
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