According to Wim Hof, the Ice Man, exposing the body to the cold, by taking an ice bath or a cold shower, contributes to losing weight. This effect occurs via an acceleration in metabolism, and with faster metabolism, more calories are burned.
This doesn’t just stem from Wim Hof.
Wired, 2013:“Exposing the body to cold can be a radically effective spur for losing weight”
SciTech Daily, 2022:“Harvard scientists discover how cold temperatures could help you lose weight”
Business Insider, 2018:“There’s more evidence that exposing yourself to cold temperatures could trigger weight loss”
MedPage Today,
2020:“Cold-induced energy burn higher with brown fat - more evidence of the tissue’s potential as target for weight loss, researchers say”
Time Magazine, 2017:“Your body is burning extra calories in response to cold. That can even translate to some
body-weight benefits… you can expect to lose some weight in response to cold”
So, what’s the story here? As part of our coaching at Triage, should we start encouraging our clients to ditch the warm showers, remove some layers, and do their training in the cold instead?
As is often the case with such claims, there is a kernel of truth, but quite a bit of exaggeration and extrapolation.
Your Body’s Response to Cold
Cold exposure does indeed cause the body to exhibit specific physiological responses. As you can imagine, it makes sense that your body would respond by ramping up processes that
generate heat or reduce heat loss to the environment. Some obvious examples that you can clearly observe are shivering (muscle contractions to generate heat), peripheral vasoconstriction (constriction of blood vessels at the skin surface to reduce heat loss), and piloerection (better known as goosebumps; hairs standing up on your skin, keeping heat close to the surface). One of these responses is less intuitive, and certainly not observable: Brown Adipose Tissue
(BAT).
BAT is a type of adipose tissue (body fat) that is responsible for the process of non-shivering thermogenesis (Tansey & Johnson, 2015). It is more metabolically active than its white counterpart (WAT), which makes up the majority of fat cells
(adipocytes). Normally, when we produce energy (ATP) through metabolism, we want there to be optimal coupling between the energy in (e.g. carbs consumed) and energy out (ATP produced). However, we are not 100% efficient, so there is often heat generated in the process that is somewhat of a “waste” from an energy perspective, but is useful for keeping us warm. The advanced details of these metabolic processes are beyond the scope of this article, but are covered in our Nutrition Certification for those who’d like to go deeper. For now, understand that what this means is that, the greater the uncoupling present, the more heat we produce through metabolism.
The presence and function of BAT in adult humans was established just in the last decade or so, as it was previously thought that BAT was more or less irrelevant beyond the neonatal stage of human development. This has brought excitement and interest in the area of BAT and the so-called “browning” of adipose tissue (there is a spectrum, white-beige-brown) as an avenue for obesity prevention and treatment, as there
exists both “classical” and “inducible” BAT cells, raising the question as to how we might activate more of the latter.
van der Lans, A. A., Wierts, R., Vosselman, M. J., Schrauwen,
P., Brans, B., & van Marken Lichtenbelt, W. D. (2014). Cold-activated brown adipose tissue in human adults: methodological issues. American journal of physiology. Regulatory, integrative and comparative physiology, 307(2), R103–R113. https://doi.org/10.1152/ajpregu.00021.2014
Above, you can see a list of all studies since 2009 demonstrating the
prevalence of cold-activated BAT in adult humans (Van Der Lans et al., 2014). Cold, thus far, is the most widely tested activator of BAT. Therefore, we can confidently say that an increase in metabolism in BAT does result from cold exposure, and that this seems to occur to the greatest extent in the neck and thorax.
Adaptation to Cold
Can we say with any certainty that any of this actually plays out in physiological changes over time?
It seems so. In outdoor workers, necropsies demonstrated a higher prevalence of BAT, which has also been confirmed by other methods assessing BAT activity and
non-shivering thermogenesis levels in those who have acclimatised to the cold (Huttunen et al. 1981;Vybiral et al. 2000;Van Der
Lans et al. 2013). This tells us that the prevalence and activity of this BAT can likely be increased by chronic cold exposure.
However, it is, as usual in biology, more complicated. The story doesn’t end there. We mentioned above that uncoupling in BAT contributes to thermogenesis (heat generation), but this also takes place in skeletal muscle. Blondin et al. (2017) found that, in response to 4 weeks of cold acclimation, coupling improved in skeletal muscle, resulting in no net change in muscle ATPase-independent thermogenesis. Practically, this means that whole-body thermogenesis would be maintained.
This brings us to the core
question: do we have any evidence that actually demonstrates increased energy expenditure or fat loss?
Does Cold Lead to Greater Calorie Burning?
The most recent meta-analysis assessing the effect of acute cold exposure on energy metabolism found that cold exposure resulted in a boost in calorie burning of 188 calories per day (Huo et al. 2022). This meta-analysis summarised the results of 10 studies, with cooling protocols ranging from 1 hour to 12 hours. Therefore, this may not translate well to the 3-10 minute exposures most frequently seen in ice-bath users.
It’s important to note that the increase in energy
expenditure results from both shivering and non-shivering (BAT), so while all the excitement often relates to the latter, shivering is still relevant. In more extreme cooling protocols (in water at 8 degrees celsius for 70-minutes), peak shivering intensity has been demonstrated to result in close to 5 times resting energy expenditure (Eyolfson et al. 2001). This is the equivalent of a light jog on
a treadmill for most people, and thus this would likely result in a significant increase in acute energy expenditure.
What you can probably gather from this is that, while we can increase energy expenditure through cold exposure, the level of discomfort is likely disproportionate to the same duration of exercise, while resulting in less energy expenditure than the
exercise would produce (and without the increase in fitness, of course). Therefore, while I am somewhat confident in saying that cold exposure can boost your energy expenditure, it seems to be a very inefficient way of doing so, unless you are undergoing such exposures for other reasons (e.g. to acclimate to the cold).
Lichtenbelt, W. van M., Kingma, B., van der Lans, A., & Schellen, L. (2014). Cold exposure – an approach to increasing energy expenditure in humans. Trends in Endocrinology & Metabolism, 25(4), 165–167. doi:10.1016/j.tem.2014.01.001
In summary, ambient temperature probably plays some role in changes in body fat over time. How significant this is is difficult to say. As you can see in the image above, getting just a little cold allows us to escape the thermoneutral zone (TNZ), remaining in the thermal comfort zone (TCZ), while still availing of some increase in metabolic rate via non-shivering
thermogenesis (NST) (Lichtenbelt et al. 2014). It’s probably not a great strategy to spend your entire day shivering; is fat loss really worth that?
Overall, there is some truth to the claim that cold exposure impacts energy metabolism, and although it’s often
exaggerated, we may be too comfortable in our cosy homes for our own good.
