‘No pain, no gain” goes the saying, though in the case of weight loss, ‘no pain, no loss’ might be more accurate. The internet is littered with articles claiming that you can effortlessly ‘melt belly fat overnight’, usually by smearing something on your abdomen or eating something disgusting before bed. Unfortunately, I was unable to find any randomised, placebo-controlled trials on the effects of onion and toothpaste sandwiches. But perhaps there could be a way to lose some weight with relatively little effort: hitting the sauna.
In previous articles, we’ve talked about how prolonged exposure to cold temperatures can encourage weight loss by promoting the development of brown adipose tissue, a type of fat tissue dedicated to burning fat to produce heat. Could exposure to heat have similar effects on weight, or is it too good to be true? Let’s take a look.
A sauna is an enclosed, heated room traditionally used for relaxation and to improve physical health. Dry saunas are usually heated by pouring water onto heated rocks, while wet saunas are more akin to steam rooms. Infrared saunas instead emit infrared light to transfer heat directly to the body. In all cases the effects are similar: a slight increase in body temperature triggers thermoregulatory responses – the body does everything it can to maintain its core temperature within the narrow range of 36.5-38.5 degrees Celsius.
The thermoregulatory responses experienced in a sauna are similar in many ways to what occurs during a session of moderate exercise – most notably in the response of the cardiovascular system. Blood is diverted to pass closer to the surface of the skin in order to aid heat dissipation, the heart beats more rapidly, and blood pressure increases during a sauna session. There’s now a good amount of evidence to suggest that this results in long-term benefits for cardiovascular health, such as reduced blood pressure.
Sauna use also mimics some of the effects of exercise at the molecular level, making cells more responsive to the blood sugar-lowering hormone insulin, and boosting the production of nitric oxide, an important molecule for blood vessel health. Sauna use also results in the activation of molecules called heat shock proteins. This is a normal cellular response to stressful conditions such as excessive heat, and puts cells into a kind of ‘defence mode’, in which they prepare to resist further stressors. For example, heat shock proteins protect against damage from inflammation and encourage the repair of damaged proteins and DNA.
A single sauna session will result in a small reduction in weight due to the loss of fluids during sweating, but weight will return to normal upon rehydration. The more pertinent question is: does sauna use contribute to long-term weight loss?
Unfortunately, the best answer we can give for the moment is ‘sort of’. As discussed, the heart works harder while you are in the sauna, which does technically increase its calorie consumption. However, even with this increase, the calorie consumption of the heart is still lower than that which the rest of the muscles in your body require at rest. Indeed, you may well burn more calories on your way to the sauna than you will inside it.
The dream of effortless weight loss in the sauna may be dead, but that doesn’t mean that saunas can’t be used as part of an effective weight loss routine. Since sauna use stresses the cardiovascular system in ways similar to moderate exercise, it could help people to better resist those stressors when they encounter them during actual physical activity, thereby allowing them to exercise harder and for longer and to recover faster. Sauna therapy immediately before or after training may also enhance the beneficial effects of exercise.
There’s some evidence to back this up: for example, a small study in middle distance runners. They found that post-exercise sauna use reduced body temperature and increased running speed and peak oxygen consumption during exercise compared to those not using saunas. Another study found that sauna use following resistance training accelerated recovery. However, the evidence for these benefits is still quite scarce. That’s partly because this line of research is still relatively new – indeed, until recently, many assumed that blood pressure decreased during sauna use due to the loss of fluids, because the research simply hadn’t been done.
Regular sauna use seems to improve general health, particularly cardiovascular health, and may improve your ability to lose weight effectively through exercise. Just don’t expect to burn any fat just by sitting in the sauna – there’s insufficient evidence to justify this as a tool for real weight loss.
The blood pressure and heart rate during sauna bath correspond to cardiac responses during submaximal dynamic exercise: https://doi.org/10.1016/j.ctim.2019.05.002
Regular thermal therapy may promote insulin sensitivity while boosting expression of endothelial nitric oxide synthase – Effects comparable to those of exercise training: https://doi.org/10.1016/j.mehy.2008.12.020
Clinical Effects of Regular Dry Sauna Bathing: A Systematic Review: http://dx.doi.org/10.1155/2018/1857413
Effects of far-infrared sauna bathing on recovery from strength and endurance training sessions in men: https://doi.org/10.1186/s40064-015-1093-5
Acute Hemodynamic Responses to Combined Exercise and Sauna: https://doi.org/10.1055/a-1186-1716
Saunas for a Personal Health and Longevity Strategy: https://www.lifespan.io/news/saunas-health-and-longevity/
Intermittent post-exercise sauna bathing improves markers of exercise capacity in hot and temperate conditions in trained middle-distance runners: https://doi.org/10.1007/s00421-020-04541-z
Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence: https://doi.org/10.1016/j.mayocp.2018.04.008