Ah, brown fat! In 2009, three independent research groups published findings in the New England Journal of Medicine (1,2,3) demonstrating that this hero cousin to evil white fat was present and metabolically active in healthy adults. Ever since, research in the area of brown adipose tissue has exploded. As has media hyperbole! With the promise of a higher metabolism and the “melting” away of body fat, it’s no surprise that descriptions of brown fat on the internet make it sound almost mythological, kind of like a unicorn or holy grail. Which we suppose it sort of is – a type of body fat once thought to have disappeared in childhood that may hold the key to weight management? Pretty impressive stuff.
But what exactly is this lesser known type of adipose tissue and how can it potentially help you lose weight?
Prior to April 2009, brown fat was thought to be relevant only in infants and some hibernating animals; we thought that it disappeared in childhood and had no activity in adults. The findings published in the New England Journal of Medicine that month (1,2,3), however, turned that old notion on it’s head – adults DID have brown fat AND it most certainly was doing something.
What is brown fat?
While labelled as brown adipose tissue (BAT), so-called brown fat actually has more in common with skeletal muscle. White fat – the stuff we typically think about when we curse our thighs and belly – functions as a store for excess calories. Conversely, brown fat actually burns calories from fat to produce heat, called “non-shivering thermogenesis”. Brown fat gets its colour from blood vessels and mitochondria, our cellular energy factory (4,5).
The body heat generated by brown fat plays a crucial role in newborns (as well as hibernating animals) and is found predominantly in the neck, chest, upper back and around the kidneys. Since babies do not have the muscle strength and coordination to generate shivering and they cannot externally regulate their body temperature, say by throwing on a sweater, turning up the heat or moving away from a drafty window, brown fat plays a crucial role in protecting them from hypothermia. That’s why you will never have more brown fat than you did as an infant – upwards of 5% of a baby’s body fat is made up of brown fat (4,5).
Adults are not quite so lucky – it’s estimated that brown fat makes up <1% of total body fat in adults. Brown fat stores also decrease with age, increasing BMI and hyperglycemia (elevated blood sugar levels) (6).
So, what’s all the fuss about? Not only does brown adipose tissue utilize body fat stores for heat production, it can also pull circulating triglycerides and glucose from the blood to use as fuel, perhaps reducing the risk of chronic diseases like type 2 diabetes and cardiovascular disease (4,5).
How do you activate brown fat?
Activating your brown fat stores is fairly simple – lower the temperature but not enough to generate shivering. When six healthy men were put into a cold suit (19⁰C or 65⁰F) or for three hours per day, they burned an additional 250 kcalories per day (7). May not sound like much, but this cold exposure would amount to 1 pound of weight loss every two weeks! If you don’t happen to have a cold-water suit laying around, just turn down the temperature at night when you sleep.
Lee et al. (8) took five healthy male participants and altered the temperature of their sleeping arrangements for three months:
- Thermoneutral = 24⁰C (75⁰F)
- Cold = 19⁰C (66⁰F)
- Warm = 27⁰C (81⁰F)
They found that sleeping in the cold room boosted brown fat activity by 30%, while the warm environment actually decreased brown fat activity; the thermoneutral room was considered baseline. Interestingly, insulin sensitivity – how well your cells respond to insulin to decrease blood sugar – increased in the cold sleeping environment.
I can hear some athletes asking, “What about cold water therapy”? Well, cold water immersion therapy, a type of cryotherapy that’s been shown to be effective post-exercise to reduce muscle soreness (9,10), is typically done at temperatures of 10 – 16⁰C (50 – 59⁰F). This is cold enough to induce shivering.
The “magic” temperature for brown fat activation needs to be cold BUT not so cold that shivering happens, where your muscles are activated to generate heat. Once the shivering starts, brown fat activity decreases (4,5). SO far, no research (that we’ve been able to find) has looked at post-exercise cryotherapy and brown fat activation.
Is it possible to gain more brown fat?
This side of the research has been booming. If researchers can find a way to stimulate brown fat production, this would be a extremely appealing treatment for obesity. Unfortunately, the science just isn’t there yet. Increasing the amount of calorie-burning fat you have by converting white fat to brown fat, also called “browning” or “beige” fat, is a bit more complicated with no studies demonstrating lasting change. This converted “beige” fat also only metabolizes fat at about 60% that of the real-deal brown fat, and it seems from animal models that the converted “beige” fat is pretty transient.
Although some research in mice has suggested that exercise training can encourage the activation of “beige” fat, results in humans are not so promising. Norheim et al. (11) looked at the effect of a 12-week endurance and strength exercise program on markers of brown fat activity and the “browning” of white fat… they didn’t find much.
Some groups are looking at brown fat activity and possible conversion using medications that activate specific cellular receptors known to be involved in the normal breakdown of body fat. In a brand new study published last week, researchers gave mirabegron, a medication for overactive bladder, to 12 healthy subjects (12). Compared with placebo, the medication increased both brown fat activity and resting metabolic rate – by about 200 kcalories per day. Sounds very promising BUT keep in mind mirabegron is still a medication with side effects; the most common side effect is increased blood pressure, so not exactly ideal for the target population with metabolic syndrome.
No Baloney’s advice? The research on brown fat is still relatively new, and there are no proven strategies to boost the “browning” of white fat. But you can make the most of the brown fat you do have!
Reducing your sleeping temperature is likely a great place to start. In fact, melatonin may be an important cofactor in brown fat activation, so make sure to not just lower the temperature but also darken your bedroom as much as possible and limit your TV/computer/phone screen time at least an hour before bed since blue light-emitting screens can interfere with melatonin release (13). As for exercise, get outside and enjoy some cold weather activities, whether walking, snowshoeing or skiing.
See, winter isn’t so bad!