In today’s society, much of our technology – air conditioning, heated pools, goose-down jackets, portable misting fans – is designed to keep us within a comfortable band of temperatures. But humans did not evolve with these modern comforts. Instead, we evolved on hot grasslands, cold tundras, and every climate in between. As a result, our bodies developed adaptive mechanisms to deal with the extremes of hot and cold.
These mechanisms are actually beneficial to our health. Outside our comfort zone, hormones are released, metabolic changes occur, inflammation is dampened, and that’s just a few of the benefits. With enough cold exposure, in fact, even our fat tissue changes color and characteristic and starts using more energy. Not bad.
Let’s start off with proven metabolic changes that cold exposure can deliver.
In one study, exposing mice to 4℃ air (39°F) for 1-8 hours 3 times per week increased their metabolism and improved their blood sugar response. The cold hungry mice ate so much to compensate for their higher energy burn that they didn’t lose any weight.
In another study, this time on humans, young men were immersed up to their necks in cold water of various temperatures – 32°C (89° F), 20℃ (68°F), and 14°C (57°F) – for one hour. Afterward, various biomarkers were measured.
The results? Under the cold conditions, the young men’s resting metabolism increased by 93% in the 68°F water and 350% in the 57°F water. Under the warm condition, though, no metabolic change was observed.
If you wallow in cool water long enough or brave the winter frost wearing only a Speedo, eventually your muscles will start to quiver involuntarily. It’s your body saying hey, I’m going to keep you warm whether you like it or not.
This is called shivering thermogenesis, and it’s one way your body maintains its core temperature in frigid environments. Shivering generates heat (that’s the thermogenesis part), and this increase in heat means a boost to your metabolism.
Although shivering thermogenesis accounts for some of the metabolic benefits of cold exposure, the more lasting benefits come from another adaptive mechanism: non-shivering thermogenesis.
Staying Warm Without Shivering
No, shivering isn’t the only way your half-naked body stays warm on a blustery winter day. You’re also kept warm by a special, metabolically active form of fat tissue called brown fat.
Brown fat, also called brown adipose tissue, converts food energy into heat energy. It keeps you warm without you having to shiver. Brown fat, then, is your secret weapon for nonshivering thermogenesis, which is way more fun than shivering to stay warm and burn more calories.
From a body composition perspective, having more brown fat is generally a good sign. Overweight and obese men, one study revealed, had less brown fat than healthy men. In that same study, brown fat activity was also positively correlated with metabolic rate.
It makes sense that higher brown fat activity is linked to higher metabolism. That’s because brown fat is packed full of mitochondria, our cellular energy centers. More mitochondria means more energy production.
But the mitochondria that give brown fat its distinctive brown color aren’t just any old mitochondria. These special mitochondria contain a protein called uncoupling protein 1 (UCP1), which creates energy in the form of heat. That’s how you stay warm without shivering.
A bit more detail on how this works. Mitochondria need food (like fatty acids and glucose) in order to produce energy. UCP1 super mitochondria, found in brown fat, are great at turning food into energy – specifically, heat energy.
In other words, when active, brown fat burns both fat and sugar to keep you warm.
From a metabolic perspective then, brown fat is pure gold. How do you get more of it? If you’re thinking cold pool, snow angels, cold showers, ice baths, or cryotherapy, you’re on the right track.
Browning Your Fat
If you want to turn your fat brown, cold exposure is the quickest way to accomplish that goal. You don’t need to shiver, but you might have to get a bit uncomfortable.
The good news is: the more brown fat you have, the less uncomfortable cold will make you. That’s because, as we covered earlier, the super-mitochondria in brown fat keep you warm through their special, UCP1-powered nonshivering mechanism. This, in turn, boosts your metabolism.
So what kind of cold exposure is required to brown your fat? Let’s look at some peer-reviewed research.
In one 2013 study, 8 men and 9 women were exposed to cool temperatures once a day for 10 days. While the exposure wasn’t very cold, it was enough to induce a response. And the response, in both men and women, was increased energy expenditure during the procedure.
The cold group also showed significant increases in nonshivering thermogenesis after the cold acclimation period. This means that, after being in a cold environment, these men and women became better able to convert food energy to heat – an adaptive response to the cold.
Along these lines, the final (and probably most interesting) finding in the study was the robust increase in brown fat tissue observed in the 17 subjects (a 37% increase, to be precise). “The current study shows, for what we believe is the first time,” write the authors, “highly significant [brown fat] recruitment in human adults after a 10-day period of cold acclimation.”
This research proves that it doesn’t take Game of Thrones, “winter is coming”, levels of cold to induce brown fat formation. Good news for all you non-polar bears out there.
There are also benefits on the opposite end of the spectrum. For those who can handle the heat, extra health benefits might be in store. Heat affects your metabolism during exercise. In fact, prolonged exposure to heat, in activities such as hot yoga, can actually speed up your metabolic rate, one pose at a time.
Hot Exposure–Hot Yoga and Your Metabolic Rate
Although hot yoga might seem like a crazy fad, it could actually be onto something.
Both your internal and external temperatures influence your metabolic rate. The chemical reactions that occur in your body and make up your metabolism happen more quickly if the temperature is higher, as the body works harder to restore your normal temperature balance. For example, if you have a fever, your BMR will predictably jump up to a rate that’s much higher than normal to increase the rate of cellular metabolic reactions aimed at tackling that fever and getting your body back to a healthy state.
When it comes to external temperature, though, it’s only prolonged exposure to heat that raises your BMR significantly. A brief exposure to heat isn’t enough to do much to your metabolism. To really raise BMR, a longer exposure to heat is necessary. This is something more easily changeable than certain genetic or biological factors, such as age, height or gender. And that’s why so many have turned to hot yoga in the hopes of helping their BMR.
Hot yoga is one of the latest trends in the world of exercise.
Traditional yoga, the kind that’s not done in a 105-degree room, has been around for a while. Experts say it originated in India more than 5,000 years ago. It’s still popular today, and for good reasons. Practicing yoga has real health benefits like increasing flexibility, managing high blood pressure, and improving cardiovascular (heart) health. But hot yoga might be overtaking its predecessor on the popularity scale because of something even better–its link with burning more calories by increasing metabolism.
The idea behind hot yoga is simple but might seem crazy to some. Hot yoga involves performing a set sequence in a studio that’s 105 degrees Fahrenheit with a 40% humidity rate. It’s an intense workout that involves a lot of sweating, and it scares many wannabe yogis away. The founder of the practice maintains that the high heat helps increase blood flow, warm the muscles for deeper stretching, and helps the lymphatic system to release toxins through sweat.
With hot yoga, all the same benefits of traditional yoga are still present–and a few extra advantages are added, too. Hot yoga tends to get a bad rap; either people think it’s crazy, dangerous, or both.
But in reality, there’s nothing wrong with hot yoga. It can be dangerous because you will be sweating a lot in a heated room, but as long as yogis consult with their doctor beforehand, hydrate properly and watch for any signs of heat intolerance, hot yoga is safe… and remember, it’s a great way to get a workout.
So how exactly does hot yoga help? Hot yoga is often performed in an environment where the temperature is much higher than your body temperature–for example, although most yoga studios keep the temperature below 100 degrees Fahrenheit, some are conducted in 105-degree heat. Because prolonged exposure to heat can raise your BMR, hot yoga can raise your BMR, too.
Yoga is extremely beneficial for many reasons. And although hot yoga may seem like an undue, sweaty punishment, the rewards could be worth it- because of the exposure to heat, hot yoga can help speed up your metabolic rate. Not only does hot yoga reap the benefits of increased flexibility and mental strength, but it can also help support your body composition goals. Next time you are looking for a new challenge, why don’t you roll out your mat and get your sweat on?