Monday, August 26, 2013

More Thoughts on Cold Training: Biology Chimes In

Now that the concept of cold training for cold adaptation and fat loss has received scientific support, I've been thinking more about how to apply it.  A number of people have been practicing cold training for a long time, using various methods, most of which haven't been scientifically validated.  That doesn't mean the methods don't work (some of them probably do), but I don't know how far we can generalize individual results prior to seeing controlled studies.

The studies that were published two weeks ago used prolonged, mild cold exposure (60-63 F air) to achieve cold adaptation and fat loss (12).  We still don't know whether or not we would see the same outcome from short, intense cold exposure such as a cold shower or brief cold water plunge.  Also, the fat loss that occurred was modest (5%), and the subjects started off lean rather than overweight.  Normally, overweight people lose more fat than lean people given the same fat loss intervention, but this possibility remains untested.  So the current research leaves a lot of stones unturned, some of which are directly relevant to popular cold training concepts.

In my last post on brown fat, I mentioned that we already know a lot about how brown fat activity is regulated, and I touched briefly on a few key points.  As is often the case, understanding the underlying biology provides clues that may help us train more effectively.  Let's see what the biology has to say.

Biology of Temperature Regulation

As warm-blooded mammals, maintaining a stable core body temperature is essential for our survival.  Since the rate of chemical reactions depends heavily on temperature, and our reactions are optimized for 97-99 degrees F, we must maintain a stable core temperature to support core organ function.  For this reason, we have a sophisticated temperature control system that acts to maintain thermal stability, also called homeostasis (3).

As with most large-scale homeostatic systems in the body, body temperature is controlled by the brain, and particularly a brain region called the hypothalamus (3).  The brain senses changes in core temperature via "thermometers" in the brain and the abdominal cavity.  In addition, the brain uses "thermometers" in the skin to detect situations that threaten future core temperature stability (3).  In other words, if the skin is cooling rapidly, this tells the brain that the core is at risk of cooling soon.  This allows us respond to thermal challenges before core temperature is compromised.

Humans maintain body temperature by a hierarchy of sequentially deployed responses that are coordinated by the brain.  Behavioral responses are one of the first lines of defense.  Humans can use a wide variety of behaviors to maintain thermal stability, such as putting on a sweater, moving under the shade of a tree, turning on the heat, and changing posture (e.g. crossed arms and legs vs. sprawled out limbs).  These behaviors "feel good" because they are made rewarding in situations where they help maintain thermal stability.  This is analogous to how food is more motivating and tastes better when you're hungry.

Changes in the diameter of small blood vessels (capillaries) in the skin are another early line of defense against cold or hot temperatures.  In cold conditions, capillaries contract, limiting blood flow to the skin and extremities and therefore limiting heat transfer from the core to the environment.  In this scenario, the skin and extremities cool down, acting as a thermal insulator for the core.  In hot conditions, capillaries dilate to allow the dissipation of excess heat generated inside the body.  Another line of defense is sweating, which takes advantage of the large amount of heat that is absorbed by the evaporation of water.

Other lines of defense against cold are deployed later, presumably because the're energetically costly.  These include non-shivering thermogenesis (via brown fat) and shivering.  Brown fat is activated first, and if that isn't sufficient, shivering kicks in to make up the shortfall.  The brain is reluctant to deploy these strategies because they're extremely costly: you're burning a lot of calories for heat that could be used to do other useful things instead, like performing muscular work, reproducing, and building or maintaining tissues.  These lost calories may also have to be replaced by seeking more food.  Not an ideal situation in a natural environment where food may be limited and obtaining it presents risks.

The brain lets you know that it prefers not to burn calories for heat by making you feel uncomfortable.  This is negative reinforcement and negative affect, the opposite of what happens when you do something your brain 'likes'.  Shivering is uncomfortable, and brown fat activation probably also correlates with mild to moderate discomfort.  Your brain would rather you put on a sweater than waste calories through non-shivering thermogenesis or shivering.

Practical Implications

Understanding the underlying biology can often help us understand how best to apply techniques that are based on biological processes.  Here are a few points of informed speculation that I'll offer to people who are interested in cold training for fat loss or performance.

1. You don't have to lower your core temperature to activate brown fat.  The brain activates brown fat in response to perceived threats to future core temperature, including a rapid drop in skin temperature.  This is why cold showers probably activate brown fat strongly, even when the exposure time isn't sufficient to lower core temperature significantly.

2. Simply revving up your brown fat for brief periods may not make much of a difference in calorie balance or fat loss.  Like muscle tissue, what burns calories is using brown fat, not just having the capacity to use it.  Resting metabolic rate for muscle and brown fat tissue are both low, despite both tissues having the capacity to use a huge amount of fuel when activated.  You can have a highly trained non-shivering thermogenesis system, but if you don't use it for more than a few minutes a week, it may not make much difference in your body weight.  Still, having a highly trained system does make you more resistant to cold stress, which may be advantageous, and may also have metabolic benefits.  Also, it remains possible that brown fat activation has neuroendocrine effects on body fatness and metabolism that go beyond calorie use.

3. The sensors that detect temperature for the purposes of activating brown fat are not, to my knowledge, located in brown fat itself (3).  Some people have used ice packs for cold training.  There's probably no advantage to putting ice on your upper back, where brown fat is located, relative to any other patch of skin on your torso.  In fact, I might actually avoid putting ice on my upper back because the more you cool your brown fat, the slower uncoupling will proceed.  Ice may also be a weaker stimulus than cold water due to the smaller surface area of skin it targets.  Water doesn't actually have to be that cold to activate non-shivering thermogenesis, due to its high conductance.

4. If you don't feel uncomfortable at all, it probably isn't doing anything.  When the brain perceives a thermal threat, it initiates a coordinated physiological and behavioral program designed to oppose core temperature change.  Part of that program includes activating brown fat, and part of it involves making you feel uncomfortable so you'll hurry up and put on a sweater or stop standing in a cold shower and wasting energy.

To illustrate that principle with an example, if you're overheated and you get into a cold shower, it feels good.  Cold water doesn't activate your brown fat in that scenario, because it's helping you achieve thermal homeostasis, not posing a threat to it.  Likewise, some people have found ways to feel more comfortable during cold training, such as keeping extremities warm.  Since feeling uncomfortable is part of the program that the brain turns on when it perceives a cold threat, I wonder if these strategies make cold training less effective by reducing the degree of brown fat activation.  You may not need to feel very uncomfortable to activate brown fat, but if you don't feel uncomfortable at all then I question whether you're having the desired effect.

I look forward to research on these questions so we can have more definitive answers.  Any additional thoughts on cold training are welcome in the comments.


aluchko said...

I generally feel both more comfortable in cooler temperatures than other people and more. What would be involved in this kind of acclimatization? Is it a purely mental response, my brain learning that temperature X is an ordinary thing and filtering the stimulus. Is it the counter measures becoming more efficient? Or something else entirely?

Could brown fat be part of this perception, that people acclimatize to cooler temperatures by activating brown fat and raising the resting metabolic rate. And once this happens the body doesn't need to take additional measures to maintain its temperature and no longer feels cold.

Essentially I'm hoping that 4) is wrong and that we can exploit this without feeling uncomfortable :)

Thomas Hemming Larsen said...

Hi Stephan,

Interesting thoughts and I like your view of not claiming to know it all when we need more research.

I've been doing the cold showers for several months now and even though I use the coldest water possible they don't really feel cold anymore. But I usually stay under the cold water until my (pardon my language) scrotum has shrunk as much as possible. The idea is that my brain by then thinks that its cold.
On top of that I swim in the ocean several times each week.

I wear as little clothes as possible and as a very lean person I'm thinking that its actually easier to activate/recruit BAT since I'll feel cold at higher temperatures than other people. Anecdotally, I've found it much easier to adapt to cold water than cold air. I still feel cold sitting at temperatures around 15-18 degrees.

Gretchen said...

I think the brain can sometimes override homeostatic mechanisms.

Example, I discovered long ago that if I was cold and shivering while waiting for a bus, if I said to my brain, "Look, brain. I know I'm cold, but I can see the bus way off in the distance and I'm not going to freeze to death in 5 minutes," I would stop shivering, and I would also feel warmer. The shivering itself was making me feel cold.

Oddly, my brother figured out the same thing at about the same time.

Of course this wouldn't be a good idea if I were stuck in freezing weather with no way to get away.

bentleyj74 said...

How would swimming factor in?

Meghan Kennihan said...

Won't the body preferentially lay down fat around the mid-section to insulate vital organs from hypothermia when you do CT daily? Or at least hold onto more fat because of the "cold"
Sorry if this is a stupid question....

Paleo Phil said...

That's cool (pun intended :) ), Gretchen. I did something similar when I moved back from Florida to the cold-weather state of my birth. I decided that if I was going to live here that I would make the best of it and learn to like winter and cold. I saw other people doing it, so I knew it was possible. Wim Hof talking about the cold as his "friend" and a local man who swims in a lake year-round, digging a hole in the ice when necessary, further inspired me. I now prefer winter weather to summer and regret a bit the ending of each winter and look forward to the next winter.

I do also enjoy the hottest days of the summer more because I find I'm also less affected by hot temperatures, and I'm trying to learn to love summer and heat like I love cold. One nice thing about the summer is there can be a hot day followed by a cold night--an invigorating cryotherapy range within a single day. My favorite seasons for weather used to be Fall and Spring, but now their weather seems somewhat boring to me, though they still also have nice aspects for me.

I mentioned Scandinavian cold/hot cryotherapy practices in a comment to Stephan's last post on brown fat, but I neglected to mention another famous example: the "caldarium (hot bath), the tepidarium (warm bath) and the frigidarium (cold bath)" of the ancient Roman baths. (

Scott Sterling said...

Does this mean Dr jack Kruse is no longer persona non grata in the paleosphere?

DancinPete said...

Hi Stephan

Won't increasing your BAT recruitment just cause other homeostatic mechanisms to kick in to counteract the additional calorie consumption? ie: won't you just eat more to offset the energy being used?

fredmull said...

not that special according to this scientist.

Jane said...

Stephan, a few months ago Jim Johnson sent me a review on browning of white fat which was then in press. It's very interesting because the central player is PPAR alpha, which I knew activates transcription of fat-burning genes in the liver, but wasn't sure it did the same thing in adipocytes. The paper is long and technical, and I thought your readers might like to see some notes I made.

The UCP1 gene has an enhancer for PPAR gamma and PPAR alpha

PPAR gamma is needed for WAT and BAT development [and can make you fat] while PPAR alpha does the WAT --> BAT switch

Thermogenic activation downregulates PPAR gamma in mature BAT

Enriched environment --> browning of WAT and leanness via hypothalamic BDNF

Thyroid hormones and vitamin A promote browning, and vitamin D may inhibit it

Leptin --> browning via central effect on SNS + upregulation of beta-3 adrenergic receptor in WAT

Beta-3 adrenergic receptor upregulates PPAR alpha in WAT

Leptin induces PGC-1alpha [which makes new mitochondria] and PPAR alpha in isolated white adipocytes

PKC beta [notorious obesity gene induced by high fat diet] downregulates beta-3 adrenergic receptor in WAT

Irisin [new browning hormone]upregulates PPAR alpha in adipocytes

High fat diet usually but not always upregulates UCP1 in BAT and downregulates it in WAT

Stephan Guyenet said...

Hi Jane,

The problem is that there's no evidence for browned white adipose tissue in humans. Rodents are a lot better at non-shivering thermogenesis than we are and so I don't necessarily expect humans to be able to do it.

Jack LaBear said...

My brain regulates my temperature by controlling how much thyroid hormone I put in my mouth.
In summer I take less so that I don't suffer from the heat, and in winter I take more so that I don't suffer from the cold ;-)

Jane said...

Hi Stephan
Well in a way I'd have to agree with you. But have a look at this quote about PPAR alpha from the review.

'Genetic [78] and biochemical [44,138] studies suggest that one aspect of the biological effects of PPARα activation is to promote a
BAT-like phenotype in WAT depots, acting through the induction of
the master regulators PGC-1α and PRDM16 [44]. In keeping with
this concept are observations that PPARα agonists (bezafibrate,
GW7647, WY-14,643) induce mitochondrial biogenesis and fatty
acid oxidation in human [154,155] and murine [156] white adipocytes
in culture. ..'

So the same thing happens in human adipocytes in response to PPAR alpha activation as happens in rodent adipocytes. One has to conclude at the very least that the machinery for browning is there. It all seems to depend on mitochondrial biogenesis, and since the 'normal' human diet these days is deficient in nutrients mitochondria need, perhaps it isn't surprising that so far there's no evidence for browned white fat in humans. Or perhaps there is evidence, in people like Wim Hof, but it's difficult to demonstrate.

You may remember a paper I posted earlier about PPAR alpha, suggesting that its endogenous ligand is a phospholipid product of de novo lipogenesis.
Insofar as DNL in adipocytes is dependent on insulin, this would suggest, would it not, that insulin can make you thin just as well as it can make you fat.

Paleo Phil said...

Scientists have been studying brown adipose tissue in Wim Hof and his students: Wim said the research on his students will be published soon and all he can say is that the results were good.

Heard this on 60 Minutes--Cold shock causes the spleen to release oxygen-rich blood:
“Just like dolphins, when we go into cold water a reflex kicks in which slows down our pulse; shifts blood from our extremities to our heart and to our brain. Our spleen contracts releasing oxygen rich blood into our arteries.” Death-defying free dives push boundaries, 60 Minutes Overtime,

This is the mammalian diving reflex that is triggered by cold water on the face.,

Paleo Phil said...

Evidence of increased expression of genes involved in nonshivering thermogenesis in response to winter climate in humans, influencing "the global distribution of allele frequencies in UCP1 and UCP3" genes:

Population Genetic Analysis of the Uncoupling Proteins Supports a Role for UCP3 in Human Cold Resistance, Anna Di Rienzo et al,

Kerwin. said...

I wonder if this physiological effect explains the huge amounts of calories freedivers and spearfishers need to consume after a session of diving in cold water, even with a wetsuit.

Water temps where I dive often hover around 55 degrees Fahrenheit, and diving sessions last 2-3 hours with almost continuous submersion.

Interesting article, thanks for the writing.

Ramon INGA said...


There is some people having had success with cold showers,bains dérivatifs.Both activate the brown fat.Both helped me to sleep better.


gunther gatherer said...

Hi Stephan, are you familiar with Wim Hof, the "Iceman"? He does incredible feats like sitting in ice for 80 minutes using breathing techniques.

Anyway, in contrast to your suggestion about brown fat and feeling uncomfortable, Mr. Hof seems pretty damn comfortable in situations that would cause hypothermia in untrained individuals.

A study on his brown fat revealed:

The experiment
To test the role of Brown adipose Wim has been thoroughly measured at the university of Maastricht for two days. The First day we measured his Brown adipose at room temperature (neutral) and the next day in a cold environment (11 degrees Celsius) for two and a half hours . We have measured the following:
- Brown fat adipose
- Heatproduction while exposed in the cold
- Bodytemperatures
- Heartbeat and bloodpressure
- Skinbloodflow
- Heatproductive capacity oif the muscle
- Bodycomponements (fat, fatfree and bonemass)

While the experiment was ongoing the body can do two things, generate heat and closing the skinbloodflow, or decreasing it.
The way Wim did it was comparable with Young adults (Wim is 52 years). Remarkable was that Wim produces the same amount of Brown adipose and in some cases even more than young adults. An average of 35 % in comparison to the 0 to 20% of youg adults, and at peaks Wim even raised over the 50 % above the normal.
Has Brown adipose been the reason of this enormous heat production while exposed in the cold?
In the PET Scan in thermo neutral conditions we have seen no Brown fat, however in the cold it showed that he had as much as Young adults. Interesting therefore is that Brown adipose partially contributed to effectively generate heat thus we can conclude that cold exposure takes care of maintaining Brown fat.
We can conclude that Wim in cold exposure feat is able to generate heat enormously and that Brown adipose is partially causing this. The other conclusion of that muscle tension and or contraction is responable for the heat production we still do not know as we still could not measure this adequately. Wim’s conviction is that concentration (will and control) are absolutely part of the process to maintain body temperature in extreme cold conditions. Another interesting fact is that people at middle age and older are capable to activate Brown adipose after training in the cold.

van Marken Lichtenbelt WD, Vanhommerig JW, Smulders NM, Drossaerts JM, Kemerink GJ, Bouvy ND, Schrauwen P, Teule GJ 2009. Cold activated brown adipose tissue in healthy men. N Engl J Med 360:1500-1508.
The research team:
Wouter van Marken Lichtenbelt
Maarten Vosselman
Boris Kingma
Guy Vijgen
Team Nuclear Medicine

So it seems you can still train yourself to "like" the cold and it doesn't diminish the benefits. At least with Wim. Cheers.

Stephan Guyenet said...

Hi Gunther,

Thanks for the references. People enjoy going for a jog, but there is still discomfort involved, which is why it requires motivation. It's less comfortable than sitting on the couch. I seriously doubt Wim Hof is totally comfortable sitting in that cold water, even if he enjoys it. I enjoyed my cold shower this morning, but it was definitely uncomfortable.

Bris said...

Humans evolved in the East African Highlands. The EAH climate is a relatively cool 15C-25C (59-77F) year round.

Modern Westerners wear far too many clothes and keep their living spaces far too warm. This is probably a major contributor to obesity.

Gretchen said...


I doubt it. People in tropics live in heat, and Inuit used to keep their igloos so hot they took off their clothing when inside. Both types of people weren't fat.

Jane said...

HOT igloos??

Vincenzo Tortora said...

It was interesting to see what happened if the cold was "somministered" during fasting/or overfeeding.

I speculate that fasting + "bout of cold" could have a duplice impact on mithocondrial function, potentiating the process that conduce to heat production.

The fasting induce improvemente in mithocondrial function/size/number; the cold induce BAT activation -> fasting + cold = increased mithocondrial function (also) in BAT -> increased heat production (compared to cold alone)

What do you think? :)