I have many patients who get the impression that staying healthy is not a year round responsibility.  They tend to focus on physical activity and healthy eating when the weather warms up, but during the fall and winter months, they think they can magically transform into a hibernating bear that is mostly sedentary, consuming excess calories and storing extra body fat despite sitting in heated homes and offices instead of an ice cold cave.

Unfortunately we are not hybrid human-bears and I see cardiovascular risk factors go up during the winter with elevations in body fat, blood glucose, cholesterol and other key health markers.  Believe me, if we were metabolically designed to hibernate and overeat from October to February/March, I would be ecstatic.

By the way, just wanted to finish off my bear analogy and why we aren’t bears.  Bears actually hibernate primarily due to limited access to food in the winter, rather than a mechanism to stay warm.  That’s just an added bonus.  Bears can lose between 25-40% of their body weight during hibernation (burning ~4,000 calories daily) because of caloric deprivation, and so rely on their extra body fat stores for energy.  My hibernating patients unfortunately consume even more calories in the winter thanks to holiday feasting and travel which is why their numbers go haywire.

In this post I’ll discuss how you can use cold weather and just plain cold exposure to your advantage, not just during the winter, but year round.

Brown Fat (aka “BAT”)

Body fat is not just an inert calorie storage container.  It comes in different forms.  If you are familiar with my work, you should know about the dangerous visceral (aka “belly”) fat that releases dangerous chemicals that raise the risk of diabetes, heart disease and cancer.  If not, read my post here.  The other type of fat is called subcutaneous adipose tissue, which is often abbreviated SCAT or SAT.  I’ll refer to it as SAT in this post.

SAT comes in 2 major flavors, white adipose tissue which I’ll refer to as WAT, and brown adipose tissue which is commonly referred to as BAT.  WAT is relatively inactive metabolically and does serve more as a fat (aka triglyceride) storage container.  However BAT is metabolically active and helps increase our caloric expenditure by soaking up glucose and fats from our blood and converting them to energy in the form of ATP.  The conversion to energy takes place in tiny powerplants inside these fat cells called mitochondria, and it’s the increased presence of these mitochondria that gives BAT its characteristic brown color in comparison to the paler WAT.

Aside from converting nutrients like glucose and fats into energy, the increased ATP generation along with the increased expression of a protein called UCP-1 (aka thermogenin), also helps generate heat, to maintain core body temperature in colder exposures.  Newborns have a greater amount of BAT than adults since the brown fat helps keep their tiny bodies warm.

Now here’s where things get even more interesting.  Individuals with ancestral origins from warmer climates have less of the metabolically active brown fat.  This makes perfect evolutionary sense.  If you are coming from a tropical climate where average temperatures are between 90-100 degrees F (32-38 degrees C) along with humidity, the last thing you want is for your body to generate even more heat.  For example, this 2014 Dutch study published in the Lancet showed South Asians (warmer ancestral climactic origin) had lower volumes of BAT compared to Caucasians (colder ancestral climactic origin) and as a result, a lower resting energy expenditure.

How much difference can having active BAT make in terms of daily resting caloric expenditure?  Studies estimate that maximally stimulated BAT can contribute to as much as 20% of daily energy expenditure.  Now if you look at ethnic groups from warmer climates who are now living in modern, air-conditioned environments like Asian Indians, Native Americans, and Pacific Islanders, they share something in common.  Some of the highest rates of diabetes in the world.  I’m not saying a lack of BAT is the sole culprit, but clearly having less metabolically active BAT while living in a sedentary, often temperature-controlled environment is not helping.  Another example of how a gene that protects certain ethnic groups in their native environment, more specifically native climate, becomes maladaptive in today’s modern environment

How to Increase BAT?

Now that you understand the science of BAT, the next question is can we increase it in an effort to boost our metabolism to help us burn more calories even as we sit around (aka resting energy expenditure)?  The answer is yes.  Exposure to cold activates our sympathetic nervous system, which then triggers BAT formation.  The sympathetic nervous system is the stress or what’s known as the “fight or flight” arm of our nervous system.

In addition to triggering BAT formation, cold exposure can also induce “beiging” of WAT.  Beiging means cold exposure can metabolically jump start inert WAT cells into burning some glucose and fat for energy.  This is a good article on how cold exposure and exercise influence BAT formation and beiging.

The real question is how much cold exposure will it take to trigger BAT formation?  Unfortunately there is not great data out there yet on optimal timing and degree of exposure.  Most studies are done in animals and many of the human studies involve durations of cold exposure that are not practical for most.

I’m going to make some cold dosing recommendations based on the existing science and my own personal experience.  An easy way to think of dosing cold exposure is to compare it to exercise, another sympathetic nervous system activator with health-promoting benefits.  Like exercise, too little will have minimal effect and too much can have risks.  I know firsthand because I overdid my cold exposure which I’ll discuss later under the “Wim Hof” section.

A few of my guidelines are as follow:

  • If you are someone who is already cold intolerant, then you need to start with lower doses of less intensive cold exposure.  I had to start like this due to my poor cold tolerance.  It always takes me forever to get into a chilly pool or a cold ocean….Brrr!  Remember, if you are not in great “cold shape,” overdosing on cold may cause more harm than good.  By the way, being excessively cold intolerant can be a sign of an underactive thyroid, so check with your doctor on whether testing is indicated.
  • If you handle cold fine, then you can start off with higher doses and longer durations of cold exposure.  My cold shower section gives tips on adjusting your cold exposure based on your tolerance.
  • As you go through your cold conditioning program, pay close attention to whether you are making progress.  Are you able to handle longer durations and more intense cold doses without feeling unbearably cold or more objectively, without shivering or getting goosebumps? Just like exercise, track your progress.  Improving your cold tolerance is a sign your body is able to generate more heat, which also means you’re burning more calories.  That’s a good thing!
  • If you are starting to “crash” in the afternoon after a morning cold session (shower, outdoor exercise, etc.), just like you might from a strong dose of coffee or an intense workout, then that’s a sign you may be overdoing it.
  • Be safe.  I have a lot of highly motivated Type As who follow my work and I want to remind them that there is a deadly condition called hypothermia which can result from overzealous attempts at cold therapy.  If you have a heart condition or other chronic health conditions, be especially careful and consult with your doctor.

Right now I would suggest you consider adding some amount of cold exposure into your weekly routine and as your body adapts, you can gradually increase the dose.

Cold Walking

I absolutely love combining cold exposure with vigorous walking.  At the time of me writing this post, we are going through a cold spell by California standards.  The morning temperatures have been below 40 degrees F which to me is perfect.  I dress very lightly, sometime just t-shirt and shorts and then start walking vigorously.

What I love best about cold weather walking is that I can get my heart rate up into a great fat burning zone (115-120s for my age) without breaking a sweat.  Below is my Apple watch during a cold weather 15 min walk during my lunch break.  I’m walking at a brisk pace just under a 14 min mile with a heart rate of 120 bpm and by the time I finished, I felt warm but didn’t break a sweat thanks to our cold winter weather.

I also felt fantastic and got a ton of work done after lunch thanks to the doubly energizing impact of physical activity and cold weather exposure…beats a cup of coffee any day!  If you’re not sure what your ideal fat burning exercise zone is, be sure to read my post here.

Smart watch

Although I typically do cold walks or jogs in the morning before work, I can also do cold walks at work between meetings or during lunch break since I don’t have to worry about my work clothes getting drenched in sweat.  Cold walks are also incredibly invigorating, so they can jump start your day or give you a boost in the afternoon to avoid that post-lunch slump in energy.

For those of you living in really cold parts of the world, I hope this might help you appreciate your cold weather as a free way to get an energy boost.  There are people paying large sums of money in Beverly Hills and other affluent warm areas to get exposure to the temperatures that you have free access to.  Take advantage!

Also keep in mind that if you do a fasted cold walk or jog, you are combining 3 energizing, fat-burning strategies into one…exercise, cold exposure and fasting.  This is like taking a powerful, but all natural combination pill that helps your body produce more energy out of glucose and fat.  Like any combination pill, because the individual ingredients work synergistically, you don’t need to do any single one to an extreme.  An overnight fast of 12-16 hours and a vigorous walk (no need to sprint or run) in cold weather, or topped off with a cold shower (see next) can work together effectively.

Cold Showers and Baths

I used to hate cold showers and if given the choice, I would always opt for a hot shower, but I have to say that even short doses of cold showers are incredibly invigorating.  If you cannot fathom your entire shower being ice cold, introduce the concept of what I call “Tabata showers” or “Cold interval showers,” where the cold exposure is analogous to a brief period of intense exercise.

Tabata is a form of interval exercise where you sprint or exercise at maximal intensity for 20s and follow that with a 10s rest period and repeat this 8 times for a duration of 4 minutes.  A Tabata shower would be done as follows:

  • Warm-up with lukewarm water for 1-2 minutes.  This is optional but may help the transition to cold if you are excessively cold intolerant or just a beginner.
  • Turn the dial either to maximum cold or almost maximal cold and do a 20 second countdown.  If 20 seconds is too much, do a 10 second countdown in the beginning.  If your shower takes a little time to get cold, only start counting when you are at the desired temperature.
  • Switch back to warm for 10 seconds.  Then repeat this sequence 6-8 times.
  • As your cold tolerance improves, you may not need a warm-up phase and you can do longer periods of cold exposure or even do an entire cold shower.
  • I also like to do slow, deep breathing during the period of cold exposure.  Training yourself to be calm, centered and to breathe slowly during intense cold exposure (a form of stress) can help your nervous system remain calm during emotional and other forms of stress
  • If cold showering becomes easy enough, you can graduate to ice baths.  Ice baths are great for recovering from intense workouts to reduce muscle soreness or as a way of really taking your cold workouts to another level to enhance BAT formation.
  • I also like to come out of the shower into a cold bathroom and wait a couple of minutes before toweling off. Again, providing an additional dose of cold for my body to adapt to.

Below is an image of a shower dial in one of our guest bathrooms where I often shower.  I put some numbers to represent different temp levels like a clock face.  The 6 o’clock position is the off position, right after maximum cold.  12 o’clock is medium temp, so as I go clockwise from 12 o’clock, the temp drops. If I go counterclockwise from 12 o’clock, the water gets warmer.

When I’m cold adapted, I can just go right to 6 o’clock and hang out there for the entire shower.  Other times when I just am not feeling like a cold shower, I do the intervals where I go to 2 or 3 o’clock for 20 seconds and then back to 12 o’clock for 10 seconds and then go colder on the next set and so on.  You get the picture.

Sorry to get this detailed, but I find having this literally “dialed in” has really helped me cold adapt and I now look forward to these sessions.  The ice cold baths are a different story and I haven’t incorporated those on a regular basis yet, but plan on doing so.

Shower handle

I don’t do cold showers every day.  I still love hot showers and so cold showers might be dosed anywhere from 2-4 times a week.  Some mornings I may not have much time to exercise, so I might just combine fasting with a cold shower and an occasional small dose of caffeine.  I don’t drink coffee on most mornings, so when I combine a little caffeine with fasting, exercise and/or cold exposure, together they pack a powerful punch!

Wim Hof Technique

If you’re not familiar with the Wim Hof technique, I encourage you to watch this video which does a great job of explaining the science and then watch a tutorial video by Wim Hof (aka the “Ice Man”) here.  Wim Hof’s feats are legendary and scientifically proven and you can read about them here.

The Wim Hof technique combines a specific breathing technique inspired by Pranayama, followed by progressive breath holding, cold exposure and then exercise.  I practiced Wim Hoff nearly every day for close to a year.  I was completely hooked and it was the closest thing I had ever felt to being superhuman.  I was able to hold my breath after blowing all the air out of my lungs for nearly 5 minutes (my personal record), I set personal records on lifting and running speed and endurance, and I had some incredible meditation sessions after Wim Hof.

So why didn’t I continue?  I realized that I had become addicted to my own adrenaline surges and over time started experiencing some increasing fatigue and sleep issues.  I talked earlier about the powerful potential combination of fasting, cold weather exposure and exercise.

Adding on breath holding and on some days caffeine would enhance adrenaline release even more.  My body became so dependent on this sensation that I would jolt out of bed between 4-4:30a to go for an outdoor run in just a t-shirt in 30-40 degree weather.  When I looked in the mirror, I felt like I had prematurely aged, despite being leaner and stronger.  I essentially had partially burned out my adrenal glands in my overzealous efforts at Wim Hof.

Now keep in mind that many individuals have felt sustained benefit from doing Wim Hof over longer periods.  They may have greater cold tolerance, they may have dosed Wim Hof in a more rational way, or they may be unaware of the fact that they are having some side effects due to the masking effect of adrenaline.

Many of us are addicted to our own adrenaline surges and don’t even realize it. Beware of this slippery slope since it can take its toll like it did for me.

I also mentioned some of the differences in BAT distribution among ethnic groups.  Individuals with ancestral origins from warm climates like South Asians, who have less BAT, likely have less cold tolerance capabilities.   If you’ve ever visited a country like India in the winter, you’ll notice locals wearing sweaters, hats, and scarves when the temperature is 70 degrees F.  Their dose of cold exposure and practices like Wim Hof might have to be less intense, at least in the beginning.


In an individual who is at high risk for heart disease, the dose of stressors like cold exposure and exercise must be managed sensibly.  Due to the nature of my work, I have come across many individuals who had a fatal or near-fatal heart attack while exercising.  Although exercise can reduce our risk of cardiovascular disease, in someone with an unstable plaque in their arteries, an excessive dose of exercise can be the final straw.

Exercise and cold exposure in someone with a dangerous plaque in their coronary arteries can be a deadly combination.  The combined stressor of exercise in a deconditioned person with the constriction of blood vessels from cold exposure can be a huge stress to the heart.

Read this Harvard summary which discusses heart attack risk from shoveling snow.  The key point of this article is typically individuals who are at risk are those that don’t regularly exercise, but all of a sudden are shoveling hundreds of pounds of snow as a necessity so they can clear the driveway and get to work.  Now even if you don’t live in a snowy region, but you are a normally sedentary person who all of a sudden decides to run outdoors in ice cold weather, you may be putting yourself at risk.  Talk to your doctor if you are unsure, but generally err on the side of slow and gradual progress with any exercise regimen.  Cold strolls outdoors might be a good starting point.

Finally, from personal experience be aware that exercising in cold weather can increase your risk of a musculoskeletal injury.  I threw my back out once because after doing some low intensity running outdoors, I decided to hit the playground equipment at the local school and do pull-ups and other body weight exercises despite not being adequately warmed up.

Food and Brown Fat

Apart from cold exposure, emerging science is showing that specific nutrients can increase brown fat formation.  Capsaicin, the active ingredient in spicy foods, is at the top of the list.  Other nutrients include turmeric, resveratrol, and green tea to name a few.  This is based on studies done in animals, so before you start opening up your wine bottles and chili pepper containers, we do need to validate this in human studies.  A nice review article on this topic can be found here.


Hopefully this post has equipped you with another powerful tool in your wellness toolkit which when used properly can help boost your metabolism and energy levels.  A bigger point I want to make is that modern humans have gotten used to being too darn comfortable 24 hours a day, 7 days a week and that is having dire health consequences.

Heaven forbid we experience hunger, some physical pain from exercise, or a deviation in temperature that may make us feel really cold or really hot.  Intermittent doses of stressors in the form of fasting, exercise, extreme cold, or heat exposure are adaptive and we call the adaptation to these stressors hormesis.  These adaptive changes at the cellular level promote longevity and can reduce our risk of chronic disease.

Based on the potential benefits of certain stress-induced adapations, the saying “what doesn’t kill us makes us stronger,” might have some truth to it.  So give cold exposure a try and see what it does for your energy levels, metabolism, body composition, and overall health goals.