Research Review: More play, more brown fat? | Precision Nutrition

Research Review: More play, more brown fat?

By Helen Kollias, Ph.D.


Getting leaner and revving your metabolism could be as simple as playing.

Want to get leaner?

Many people think, “Sure, but that means I have to eat grilled chicken breast and broccoli every day while spending hours at the gym and living like a hermit. Bo-ring!”

I often get the impression that people think being lean, fit and following a healthy lifestyle means they’ll be chained to their kitchen and gym. That they can’t go out, spend time with their friends, or — most importantly — have any fun.

Well, first, take a look at Gourmet Nutrition to find more food options than chicken and broccoli. And check out our Lean Eating Coaching Program, which will teach you how to lose weight without putting your life on hold.

But even cooler than great food and learning how to become a ninja (well, almost), new research suggests that having a more stimulating environment (aka fun and games) may help you lose weight. The key is a very special type of fat called “brown fat.”

Between fat and flesh: Brown fat

Unlike white fat, which stores energy, brown fat burns energy like muscle. In the last few years researchers (including me) have figured out that brown fat is a lot more like muscle then we’d ever imagined… and it may increase your metabolism.

For years, everybody thought only babies had brown fat (see the slightly creepy Figure 1). Scientists assumed that as we got older we gradually lost all our brown fat, so by the time you get zits and stick up Justin Bieber posters, your brown fat is gone.

But in 2009, three separate groups published three separate papers at the same time in the New England Journal of Medicine proving adults have brown fat. Whoops!

Figure 1 – Regions of brown fat in infants

Why did it take three groups publishing three articles at the same time in the same journal? It took that much convincing, because in the modern medical universe, this was equivalent to Galileo to saying the earth revolved around the sun.

I actually reviewed one of the three breakthrough articles in a Research Review.

Since then, lots of researchers have tried to learn more about brown fat by asking questions like:

  • Where is it?
  • Who has it?
  • How can we get more?

Brown vs. white fat

Brown fat is similar to white fat in its composition — both have triglycerides. Where the fats differ is their function and behaviour.

It’s a bit of an over-simplification to think of brown fat as good fat and white fat as bad fat, since having too much or too little of anything is a bad thing. Instead of thinking of good and bad, let’s think of heating (brown fat) and storage (white fat).

Brown fat uses fat to make heat. White fat uses fat for storage, insulation and cushioning.

Brown fat is similar to muscle because it breaks down fat and makes energy, but instead of using the energy to move (like in a muscle contraction), brown fat converts energy into heat.

Where is brown fat?

As you can see in Figure 1, most brown fat is between the shoulder blades, along the front of the neck and down the front of the chest to the belly button, with a bit around the kidneys.

Since the main function of brown fat is to keep us warm, it makes sense that it’s near the heart and kidneys, where a lot of blood passes to pick up heat. Think of your furnace and the vents leading away from it.

Another cluster of brown fat has been found intermixed with white fat in visceral fat. Yes, that visceral fat, the fat associated with all kinds of metabolic problems, can have metabolically active brown fat that actually protects us from metabolic disease (such as diabetes, heart disease, etc).

As an interesting aside, most methods of measuring body fat like hydrostatic weighing, DEXA and bioelectrical impedance can’t differentiate between brown and white fat. Skinfolds only measure white fat, since brown fat in humans is not in subcutaneous fat (fat under the skin). As you can see from Figure 1 above, brown fat tends to cluster deep in the body.

What activates brown fat?


In his book The 4 Hour Body, Tim Ferriss describes an apparently wacky regimen of self-cooling with cold baths and ice packs on his neck. Actually, he may have been on to something. Putting people (or animals) in a cold environment, as mild as 16°C (61°F), increases brown fat activity, metabolism and overall energy expenditure.

Sympathetic (β-adrenergic) stimulation

This is the fight or flight response that kicks in when you feel threatened. It’s part of the autonomic nervous system. It can also be artificially prompted by stimulants such as caffeine. However, before you start guzzling at the coffee pot, just be aware that nobody’s yet linked triple espressos to brown fat production.

…and play?

Research question

This week’s article looks at how an enriched environment — aka giving mice fun stuff to do — increases metabolism. Does play actually change the nature of fat? It sounds too good to be true.

Cao L, et al. White to brown fat phenotypic switch induced by genetic and environmental activation of a hypothalamic-adipocyte axis. Cell Metab. 2011 Sep 7;14(3):324-38.


Disclaimer: This study was done on mice, which is the best model we have right now for these type of studies. But we have to be careful about how we interpret the results. (Just like you shouldn’t run out and drink a venti Americano while rolling naked in the snow just yet, you probably shouldn’t immediately invest in a giant running wheel to improve your brown fat.)

Lab mice generally have a dull life.

They have a couple of siblings, as much water and mouse chow as they want, and maybe a toy like a ping pong ball, but things are pretty much the same, day in and out. They don’t even have Mouse TV where they could entertain themselves with shows like The Big Cheese or Trapped!

These mice were the tiresome, tedious controls. (Sorry about your luck, mice.)

Enriched environment

Researchers decided to create a party for one group of mice, by constructing an enriched environment.

The mice in the enriched environment lived in a bigger cage with running wheels, tunnels, igloos, hut, retreats, wood toys and a maze, but with the same number of mice (5/cage) as the control group.

Other groups included a third group that had a regular cage with a running wheel and nothing else different from the controls; and a fourth group that had an enriched environment but no running wheel.

So, to recap, we have:

  • Group 1 Control: Boredom central, 5 mice per cage
  • Group 2 Super-enriched environment: Party time, 5 mice per toy-filled cage
  • Group 3 Running wheel only, 5 mice per cage
  • Group 4 Enriched environment only (no running wheel), 5 mice per cage


After four weeks in the enriched environment, the Group 2 mice were slightly lighter, but had nearly 50% less visceral fat compared to the Group 1 mice in the controlled environment. Wow!

Well, maybe the enriched environment group was too busy to eat and they just were taking in fewer calories. Nope. The enriched Group 2 ate more than the control group (about 2 grams less a day).

Compared to Group 3 with a running wheel, the Group 2 enriched environment mice still had less white fat, as measured by 3 abdominal regions (epididymal, inguinal and retroperitoneal fat), but with no difference in body weight.

Since both groups had a running wheel, could it be that the mice in the enriched environment liked running more than the running wheel group? Nope. The enriched group ran less (0.86 km/day) than the running wheel group (2 km/day).

When comparing Groups 2-4 (enriched, running wheel only, enriched but no wheel) to the control Group 1, all had less abdominal white fat. Both enriched groups had more brown fat in the retroperitoneal region (fat right behind the kidneys).

The stimulation of the enriched environment increases a specific brain protein (brain derived neurotropic factor; BDNF) that increased brown fat by activating the sympathetic nervous system.


An enriched environment with less routine and more mental stimulation improves metabolism through a pathway called the hypothalamic-sympathoneural-adipocyte axis.

Translation: An enriched environment increases a specific protein in the brain (BDNF) that activates the sympathetic nervous system (fight or flight) that increases brown fat in visceral fat. The increase in brown fat means a higher metabolism with less visceral white fat.

More stimulation, more BDNF, more brown fat, faster metabolism leads to less white fat.

Getting leaner and revving your metabolism could be as simple as having fun. Play yourself ripped. Cool.

After discovering that having a more stimulating environment helped fight obesity through increasing brown fat and metabolism, what did the researchers conclude?

That people should have more stimulating environments, or play more, to fight obesity? Nope. They figured that hopefully someday a drug could be found to activate the same pathway that an enriched environment does. Doh!

Well, you could wait around for a drug to activate your hypothalamic-sympathoneural-adipocyte axis pathway or you can try to live a more stimulating (not stressful) life.

Bottom line

A more stimulating environment — fun stuff to do — increases metabolism of mice and may do the same for people.

Right now scientists can’t say that a more stimulating environment will increase metabolism in people since they don’t have evidence from human studies, but this is a good “self-experiment”.

Try something different, exercise your brain, go somewhere new… hell, run through a maze on occasion. What’s the worst that could happen?


Click here to view the information sources referenced in this article.

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