What is Brown Fat?
I think it’s fair to say we’ve reached a point where rampant fat-phobia is finally starting to subside.
By now, most health-conscious people know that dietary fat is nothing to shy away from. Omega-3s and monounsaturated fats from fish, olive oil, and avocado are loudly celebrated. And even saturated fat is shaking off its decades-long bad rap.
But when it comes to body fat, the story’s a little different. The idea that a little extra adipose tissue might actually be good for you is a tough sell. But if you’ve been paying attention to the emerging research on “brown fat,” then you’re already one step ahead of the game.
In case you haven’t heard of it, let me take a moment to get you up to speed — starting with a few fast fat facts...
First, let’s state the obvious: Fat serves a biological purpose. Its main role, of course, is as a stockpile of surplus caloric energy. If you’re ever stranded on an island without food, that beer gut was designed by nature to come to your rescue.
But in addition to this function, fat also has what you could call a mind of its own. It’s a metabolically active substance — which means that it broadcasts messages to your body in the form of hormones and inflammatory signals.
The first function paints a pretty straightforward picture — calories in, calories out. If you eat too much, you get fat. If you cut down your calorie intake, the fat melts away.
The problem here — and one with which you’re probably already familiar — is that it doesn’t always work this way in practice. And that’s a direct result of fat’s metabolic activity. In other words, your body’s going to do what your fat tells it to do — so the signals it’s sending are of critical importance to your health.
This is why your fat’s “type” matters — or for the sake of this discussion, its color.
Most of the fat in your body is white adipose tissue (WAT). In normal amounts, it's responsible for modulating hormones like adiponectin and leptin, two key players in appetite regulation and insulin sensitivity. But as your weight creeps up, your white fat cells grow larger — and things go haywire fast.
All this white fat throws off your body’s homeostasis — an eventually, your body simply stops listening to the signals it’s sending. At the same time, excess white fat recruits inflammatory cytokines, which pushes your metabolic balance into an even deeper tailspin.1
It’s a vicious cycle to recover from — which is why a lot of people don’t. They just get fatter. And then they get diabetes.
Brown adipose tissue (BAT), on the other hand, comprises only a few ounces of all the fat on your body. But good things come in small packages. And suffice it to say that this stuff is a different beast altogether.
That’s because brown fat isn’t there to store energy — it’s there to generate it. Brown fat’s darker color comes from its abundance of mitochondria — your cells' power centers. And one of its functions is to ramp up body heat. (This is why infants have the brown fat market cornered. Think of it as an evolutionary source of super-fuel, kicking in when other bodily mechanisms — like shivering — aren’t able to get the job done.)
Brown fat burns calories — as many as 500 in a single day. So in this respect, it behaves less like fat as we know it... and more like muscle. It’s fat-burning fat that shifts your metabolism into high gear and gobbles up white fat in the process, leaving your body leaner as a result.
So it’s no surprise research shows that lean kids have higher amounts of active brown fat than their obese peers.2 In fact, gains in brown fat appear to be closely related to gains in muscle volume all the way through puberty — particularly among boys.3
And what about adults? Well, the answer to that question might explain a few things about middle-aged weight gain...
In 2009, researchers at Joslin Diabetes Center in Boston found that, contrary to what was previously thought, adult bodies have active brown fat stores, too. (Mostly concentrated in the upper back and neck.) And that, like children, lean adults with healthy blood sugar levels have the most brown fat.4
The trouble is that brown fat declines markedly with advancing age. In fact, the Joslin researchers found that adults over 64 who also have a high BMI were six times less likely to have an ample supply of brown fat. And another study published just last year showed that — in mice, at least — biological changes associated with advancing age strip brown fat of its thermogenic activity.5
This, of course, raises more than one million dollar question. Namely, is there a way to convert white fat into brown — or to turn the brown fat you have back “on”?
Science has turned up a few possible answers in recent months. Some of them are lethal — some are completely impractical. But some of the strategies are a lot simpler than you might think. I’ll be giving you the lowdown on all of them next week. So as always...
Stay tuned and stay well,
1. Greenberg AS, et al. Am J Clin Nutr. 2006 Feb;83(2):461S-465S.
2. Drubach LA et al. J Pediatr. 2011 Dec;159(6):939-44.
3. Gilsanz V, et al. Pediatr Res. 2013 Jan;73(1):3-9.
4. Virtanen KA, et al. N Engl J Med. 2009 Apr 9;360(15):1518-25.
5. Sugatani J, et al. FASEB J. 2014 Jan;28(1):440-52.