RHR: Cold Exposure: Why Sustained Beats Extreme

In this episode we discuss:

• Why ice baths and extreme cold exposure are not the most effective way to activate brown fat
• What brown adipose tissue is and how it differs from white fat
• The science behind sustained mild cold exposure
• How extreme cold triggers a stress response that limits metabolic benefits
• Practical, accessible ways to incorporate mild cold exposure into daily life
• When ice baths do make sense

Show notes:

• “Contribution of brown adipose tissue to whole-body energy expenditure and macronutrient oxidation in humans” by Fernández-Verdejo, R. et al.
• “Minimal changes in environmental temperature result in a significant increase in energy expenditure and changes in the hormonal homeostasis in healthy adults” by Celi, F.S., et al.
• “Brown adipose tissue improves whole-body glucose homeostasis and insulin sensitivity in humans” by Chondronikola, M., et al.
• “Cold but not sympathomimetics activates human brown adipose tissue in vivo” by Cypess, A. M., et al.
• “Short-term cold acclimation recruits brown adipose tissue in obese humans” by Hanssen, M. J., et al.
• “Effect of acute cold exposure on energy metabolism and activity of brown adipose tissue in humans: A systematic review and meta-analysis” by Huo, C., et al.
• “Temperature-acclimated brown adipose tissue modulates insulin sensitivity in humans” by Lee, P., et al.
• “Activation and recruitment of brown adipose tissue by cold exposure and food ingredients in humans” by Saito, M., et al.
• “Cold-stimulated brown adipose tissue activation is related to changes in serum metabolites relevant to NAD+ metabolism in humans” by U Din, M., et al.
• “Cold acclimation recruits human brown fat and increases nonshivering thermogenesis” by van der Lans, A.A., et al.
• “Brown and beige adipose tissue and aging” by Zoico, E., et al.
• “Recruited brown adipose tissue as an antiobesity agent in humans” by Yoneshiro, T., et al.
• Learn more about the Adapt Naturals Core Plus bundle or take our quiz to see which products best suit your needs
• If you’d like to ask a question for Chris to answer in a future episode, submit it here
• Follow Chris on Instagram or Facebook

Hey everybody, Chris Kresser here. Welcome to another episode of Revolution Health Radio. I’m guessing you’ve seen the cold plunge trend all over social media. Ice baths, extreme cold exposure, people dunking themselves in near-freezing water for a few minutes at a time. The conventional dogma on cold exposure is “the colder, the better.” If you really want metabolic benefits, you need to get into that 34 degree ice bath and tough it out. This has understandably turned a lot of people off to the idea of cold exposure. After all, who really wants to get into an ice bath?

But here’s the thing, the research doesn’t support the “colder is better” dogma. In fact, a new review in The Journal of Physiological Anthropology found that sustained mild cold exposure is more effective than those short bursts of extreme cold that everyone’s talking about. That’s good news if you’ve been interested in the benefits of cold exposure but have been intimidated by cold plunging. By the end of this episode, you’ll understand what brown fat is and how it works, why moderate cold can be more beneficial than extreme cold, and what you can do to get these benefits without shocking your system. Let’s dive in.

White Fat vs Brown Fat

Okay, let’s start with the basics. Most of the fat in your body is white adipose tissue, or white fat. It stores energy for later use. But there’s another type, called brown adipose tissue, or brown fat, that works completely differently. Brown fat is packed with mitochondria, the powerhouses of your cells. Mitochondria contain a lot of iron, which is what gives brown fat its color. Unlike white fat, which stores energy, brown fat burns energy to generate heat, and that’s called thermogenesis. When you’re exposed to cold, your sympathetic nervous system kicks in and releases norepinephrine. That activates your brown fat, which starts burning glucose and fatty acids to create heat. This is called non-shivering thermogenesis. It’s your body’s way of keeping you warm without shivering. Brown fat is incredibly metabolically active. A 2014 paper in Diabetes found that brown fat activation improves glucose metabolism and insulin sensitivity. When your brown fat is active, your body gets better at handling blood sugar and using insulin effectively.

Another paper in the Journal of Clinical Investigation showed that people with more active brown fat tend to have lower body mass index, better glucose control, and improved lipid profiles. Brown fat isn’t just about staying warm. It plays a real role in your overall metabolic health. Unfortunately, we don’t have a lot of this metabolically active brown fat as adults. Babies have significantly more because they can’t shiver effectively and they lose heat quickly. But we lose most of it as we grow up. The average adult might have only 50 to 100 grams of brown fat, but even that small amount is extremely metabolically active. Studies suggest that just 50 grams of maximally activated brown fat could burn an extra 300 to 500 calories per day.

Mainstream Dogma on Cold Exposure

Okay, so let’s talk about the mainstream dogma on cold exposure. Cold plunging has become a massive trend. You see influencers and biohackers getting into ice baths at 34 to 39 degrees for two to four minutes. I was doing this myself up until a couple of years ago. The message is pretty consistent. Go as cold as you can, push your limits. That’s where the magic happens. I get the appeal. There’s something compelling about doing an extreme intervention that feels uncomfortable. It feels like you’re really doing something powerful. I’m not saying there aren’t benefits to cold plunges. There clearly are, but we need to look at what the research says. The review I mentioned earlier looked at all the research on cold exposure and brown fat activation. What they found was that sustained mild cold exposure, around 17 to 19 degrees Celsius, or 63 to 66 degrees Fahrenheit, for about two hours was more effective at activating brown fat and increasing energy expenditure than short bursts of extreme cold. So I’ll say it again, sustained mild cold was more effective than brief extreme cold exposure.

One paper in the Journal of Clinical Endocrinology and Metabolism kept participants at 19 degrees Celsius for two hours. Again, that’s about 66 degrees Fahrenheit. Not freezing. Not even close to an ice bath. They showed marked increases in brown fat activity and energy expenditure without shivering. Another study found that daily mild cold exposure for six weeks resulted in increased brown fat activity and decreased body fat.

Science of Sustained Mild Cold Exposure

Why would mild cold be more effective than extreme cold? It comes down to sustainability and the type of response your body has. When researchers measure brown fat activity, they’re looking at glucose uptake in those tissues using specialized imaging. What they find is that mild cold exposure for longer periods leads to greater total energy expenditure than brief extreme cold. The math is straightforward. If you’re in 66 degree air for two hours and burning an extra 200 calories per day, that’s more metabolic benefit than three minutes in an ice bath that might activate brown fat briefly, but doesn’t sustain that activation. When you get into a 34 degree ice bath, your body goes into crisis mode. Your blood vessels constrict dramatically, your heart rate spikes, and your body is essentially trying to protect your core temperature from what it perceives as a life threatening situation. You might activate brown fat, but you can only stay in that environment for a few minutes before it becomes dangerous. Compare that to sustained mild cold exposure. At 63 to 66 degrees, your body isn’t in crisis mode. It’s just slightly uncomfortable. Cool enough that your body needs to generate heat, but not so cold that you can’t tolerate it for an extended period. And that extended exposure turns out to be key.

A paper in Cell Metabolism found that when you expose your body to mild cold for longer periods, you not only activate existing brown fat, but you can recruit new brown fat. There’s a process called browning, where certain white fat cells can transform into beige cells that have brown fat-like properties. That process takes time. It doesn’t happen in a three-minute ice bath. There’s also the issue of what happens after the cold exposure. When you get out of an ice bath, your body is focused on warming back up as quickly as possible. But with sustained mild cold, your body stays in that thermogenic state for longer. You’re burning calories, activating brown fat, improving insulin sensitivity, and you’re doing it in a way that’s sustainable.

A meta-analysis in Frontiers of Endocrinology looked at multiple studies on cold exposure. They found that acute cold exposure at 16 to 19 degrees Celsius increased energy expenditure by an average of 188 kilocalories per day. That might not sound like a lot, but it adds up over time, and it’s happening at temperatures that most people can tolerate. Another fascinating finding comes from research on cold acclimation. A paper in Diabetes followed participants who were exposed to mild cold overnight for several weeks. Brown fat acclimation was accompanied by improved insulin sensitivity and changes in hormones like adiponectin and leptin, which play important roles in metabolism and body weight regulation. On a cellular level, the mitochondria in brown fat cells have a special protein called UCP1, or uncoupling protein 1. This protein essentially short circuits the normal energy production process. Instead of producing ATP, which is your cell’s energy currency, it produces heat. Your body is burning fuel directly to stay warm rather than storing it first. Brown fat prefers fatty acids and glucose, so when it’s active, it’s pulling these substrates out of your bloodstream and burning them for heat. That’s why you see improvements in blood sugar control and lipid profiles with regular cold exposure. Your body is consuming these nutrients to generate warmth. Sustained mild cold gives your body time to activate brown fat, recruit new brown fat, improve metabolic markers, and do all of this in a way that’s pleasant enough that you might stick with it long-term.

I first started wondering about this long before I became a functional medicine clinician. I’m a lifelong surfer, and I’ve always noticed it’s fairly rare to see overweight surfers. Now I understand why. We spend hours in water that’s often in the 50s and 60s, and sometimes colder. This isn’t ice bath temperature. It’s sustained mild to moderate cold, exactly what studies suggest burns fat most efficiently. I still cold plunge occasionally in the Deschutes River or Tumelo Creek near my home in Bend, Oregon, and I enjoy it. But this research on sustained mild cold validated what I’ve long suspected. You don’t need to go to extremes to get real metabolic benefits. I’m also an avid skier, and skiing, of course, involves being outside in cold weather for extended periods. You’re getting that sustained mild cold exposure. Your body’s working to maintain temperature, your brown fat is active, and you’re doing it in a way that’s enjoyable, rather than something you have to white knuckle through. When you think about how humans evolved, we spent most of our evolutionary history exposed to varying temperatures. We didn’t have central heating or perfectly climate controlled environments. Our bodies had to adapt to being cooler sometimes and warmer other times. That natural variation in temperature exposure is probably closer to what our physiology is designed for than the constant 72 degrees that most of us live in now.

In this episode of Revolution Health Radio, we break down the science of cold exposure and explain why sustained mild cold exposure is more effective than short bursts of extreme cold for improving metabolic health. #RHRpodcast #coldexposure #ChrisKresser

Incorporating Mild Cold Exposure into Daily Life

Here are several practical ways to incorporate sustained mild cold exposure into your life. None of these require an ice bath or cold plunge or any special equipment. First, turn down your thermostat. This is probably the easiest one. Research suggests that keeping your indoor temperature around 66 to 68 degrees Fahrenheit can activate brown fat and increase energy expenditure. It’s not freezing. It’s just cool enough that you might want to wear a sweater or sweatshirt inside. A paper in the European Journal of Endocrinology found that minimal changes in environmental temperature resulted in significant increases in energy expenditure and changes in hormonal homeostasis in healthy adults. 66 degrees might sound cold at first, but after a few days of keeping your home cooler, your body adapts. You start to feel comfortable at lower temperatures, and that adaptation is exactly what we’re looking for. That’s brown fat recruitment and activation happening in real time.

Second, spend time outside in cool weather with one less layer than you think you need. I’m not saying go outside in the dead of winter without a coat, but if you normally wear a heavy jacket, try a lighter one. Let yourself feel a bit cooler. That mild discomfort is beneficial. Your body adapts, your brown fat activates, and over time, you’ll probably find that you can tolerate the cold better. I do this all the time. When I’m walking the dog or going for a hike or even skiing, I’ll intentionally underdress slightly. Again, not to the point where I’m shivering uncontrollably, but just enough that I feel a bit cool. After 10 to15 minutes of walking or skiing or whatever I’m doing, I will warm up naturally. My body is generating that heat through movement and through brown fat activation.

Third, you can take cool showers. Not ice cold, just turn the temperature down to where it’s uncomfortable but tolerable. Start with the last 30 seconds of your shower and work your way up to a few minutes. A paper in PLOS ONE found that people who took cold showers had lower rates of sickness and absence from work compared to those who took only warm showers.

Fourth, if you have access to a pool or natural body of water, swimming in cool water is excellent. Water temperatures in the 60s provide sustained mild cold exposure. You get the added benefit of exercise and being outdoors if it’s a river or an outdoor body of water, and it’s something you can do for 20 or 30 minutes, which is much longer than you’d ever spend in an ice bath. You can also consider swimming in even cooler water in a wetsuit. Many people do that here in Oregon well into the fall and early spring, with water temps in the 40s and 50s.

Fifth, consider sleeping in a cooler room. Research shows that sleeping in temperatures around 66 degrees Fahrenheit can increase brown fat activity and may improve sleep quality. There’s some interesting research showing that cooler sleeping temperatures may improve deep sleep and help with blood sugar regulation overnight. We keep our bedroom in between around 64 and 66 degrees at night, and I found that to be a perfect temperature for promoting deep sleep and just supporting overall metabolic health.

The key with all these approaches is consistency. Doing it once won’t change much, but if you incorporate some form of mild cold exposure most days, you’re giving your body the signal to maintain and recruit brown fat, improve your metabolic health, and you’re doing it in a way that’s sustainable. The research suggests that you can see increases in brown fat activity within a few weeks of regular cold exposure. One study found measurable changes after just 10 days of daily cold exposure. But for more substantial changes in brown fat mass and metabolic markers, you’re looking at more like six to eight weeks of consistent practice. Older adults do have less brown fat than younger adults on average, but they can still benefit from cold exposure. Some studies have specifically looked at middle aged and older adults and found they can still increase brown fat activity and improve metabolic markers with regular cold exposure.

When Ice Baths Make Sense

Before we wrap up, I want to address situations where ice baths or extreme cold exposure might still make sense. I don’t want you to walk away thinking that ice baths are useless. They’re not. They just serve a different purpose than what’s being marketed or talked about on social media. For athletes, particularly after very intense training sessions, ice baths can help reduce inflammation and muscle soreness. The mechanism is different from brown fat activation. It’s about vasoconstriction reducing blood flow to damaged tissues and limiting the inflammatory response. That can be very helpful for recovery in certain situations. Ice baths can also be valuable for building mental resilience. There’s something about voluntarily putting yourself in an uncomfortable situation and breathing through it that builds psychological strength. That’s not metabolic benefit, that’s mental training, and that’s legitimate. It’s just different, again, from what we’ve been talking about with brown fat activation.

Some people genuinely enjoy the feeling after an ice bath, and I’m one of those people. That rush of endorphins and norepinephrine can be invigorating. If you’re someone who just likes that feeling and you’re doing it safely, there’s nothing wrong with continuing. Just understand that for metabolic benefits specifically, sustained mild cold is more effective. And last, time is a factor. A three-minute ice bath is certainly going to be quicker than spending two hours outside in mild to moderate cold, and given busy schedules that might be more accessible for many people.

Okay, so now I’m going to wrap this up. Here’s what I want you to take away from this episode. Brown fat is a special type of fat that burns calories to generate heat. It plays an important role in glucose metabolism, insulin sensitivity, and overall metabolic health. When you activate brown fat through cold exposure, you’re doing something genuinely beneficial for your body. But you don’t need extreme cold to get these benefits. The research suggests that sustained mild cold exposure at around 63 to 66 degrees Fahrenheit for longer periods is more effective than short bursts of extreme cold like ice baths. And of course, you’re more likely to stick with something that’s uncomfortable but tolerable than something that is borderline painful or shocking. So if you’ve been curious about cold exposure but intimidated by ice baths, I hope this episode encourages you to try it in a more accessible way. Your body is adaptable. It responds to stress in predictable ways. When you give it the right kind of stress at the right dose, you can see real improvements in your metabolic health.

The other thing I want you to remember is that cold exposure is just one tool in the metabolic health toolkit. It’s not magic. It’s not going to overcome a poor diet or lack of exercise or chronic sleep deprivation. But when you combine it with other healthy practices, it can be a meaningful contributor to your overall metabolic health.

Okay, that’s it for this episode. I hope it was helpful. You can find show notes and links to all the studies I mentioned at ChrisKresser.com. If you have questions about cold exposure or other topics you’d like me to cover, head over to ChrisKresser.com/podcastquestion, and submit your question there. I read all of them, and I use them to guide what topics I cover on the show. Thanks for listening. I’ll talk to you next time.