A sauna session can drop the number on your scale by half a kilogram or so, and almost all of that is water you'll put back with your next glass of it. The studies that have measured this directly point the same way: sweating changes your weight, but it does not appear to change your fat.
That doesn't make a sauna a bad idea. It just means the question worth asking is what you actually want out of it, because the answer changes whether it's worth your money.
The Quick Answer
Sauna weight loss is mostly fluid loss. In a study of 230 healthy men who sat through two 10-minute sessions at 95C, the average body mass loss was 0.49 kg (about 1 lb), with a range of 0.2 to 1.1 kg.1 In a separate trial where 12 men did 12 high-temperature sessions over 4 weeks, the authors reported no changes in weight and fat tissue compared with a control group.3 Research suggests a sauna may support recovery and relaxation, and it should not be treated as a fat loss tool.
Why the Scale Drops After a Sauna
When your core temperature climbs, your body sweats to cool itself down. Sweat is mostly water, so you walk out of the sauna lighter than you walked in. Step on a bathroom scale right away and it looks like progress.
The catch is that your body treats that water as something it needs back. Drink a couple of glasses and eat a normal meal, and the weight returns within a day. Fat works differently: your body has to burn it, not sweat it, and a sweat gland has no way of pulling fat out of storage.
One study of Finnish sauna sessions put it in a single sentence in its conclusions. The authors wrote that body mass loss in the sauna "is related to the loss of body fluids as a result of sweating."4
What the Research Found
A few small studies have actually put people on a scale and in a sauna, and they line up well.
| Study | Who | Sauna protocol | What happened |
|---|---|---|---|
| Boraczyński 20181 | 230 healthy young men | Two 10-minute sessions at 95C | Average body mass loss 0.49 kg (0.61%), range 0.2 to 1.1 kg |
| Podstawski 20192 | 45 overweight, sedentary men | Four 10-minute sessions at 90 to 91C | Body mass fell 0.65 kg over the 60-minute treatment |
| Toro 20213 | 23 healthy young men (12 sauna, 11 control) | 12 sessions over 4 weeks at 100C | Authors reported no changes in weight and fat tissue |
| Podstawski 20224 | 30 healthy men | Four 12-minute Finnish sauna sessions at 90C | Body mass decreased, attributed by the authors to sweat loss |
A single visit takes off somewhere between a third of a kilogram and two-thirds of one, depending on how long you stay and how big you are. When researchers repeated sessions for a month and then checked fat, the fat was still there.
A few honest caveats apply. These are small studies, all in men, and they were mostly designed to look at heart rate and blood pressure rather than weight loss, so none of them is a clean test of "can a sauna habit change body fat over a year." What they do show consistently is that the immediate weight change is fluid.
What About the Calories You Burn?
You may burn a small amount of extra energy in a sauna, because your heart works harder to push blood to your skin. In the 230-man study, average heart rate rose from about 79 beats per minute at rest to about 136 after 20 minutes of sauna.1 That is roughly the heart rate of a brisk walk.
The articles I could verify for this post did not report energy expenditure, so I can't give you a trustworthy calorie number, and I'd be wary of any sauna brand that gives you a confident one. Even if the number were meaningful, sitting in a hot room while your heart rate sits at brisk-walk levels is not going to compete with an actual walk, or with changes in how much you eat.
Who Loses the Most, and Why That Isn't a Good Sign
Larger bodies lose more fluid in the sauna. In the 230-man study, the group with the highest body surface area lost 0.66 kg, compared with 0.38 kg in the group with the lowest, and the authors found that loss tracked closely with body mass and body surface area.1
That sounds like an argument for sauna use if you carry extra weight, but the same study points the other way. The authors concluded that the physiological cost of dry sauna heat is higher in people with greater body mass, and they recommended more frequent cooling, more fluids, and no more than two 10-minute sessions on that protocol for these individuals.1 In the 45-man study of overweight, sedentary men, the authors noted that deleterious cardiovascular adaptations were most prevalent in the men with the highest degree of obesity and the largest body size.2
So the people most likely to be tempted by sauna weight loss are also the people who need to be most careful with it. If you're managing a heart condition, high blood pressure, or you're not sure how your body handles heat, talk with your doctor before starting.
Safety and Hydration
Because the weight you lose is fluid, the safe way to treat it is as fluid you owe back. Drink water before and after, and consider electrolytes if you sweat heavily. Leave the room if you feel dizzy, nauseated, or your heart is pounding in a way that feels wrong, and give yourself a few minutes to cool down before you stand up quickly.
Please don't use a sauna to "make weight," cut water the day of a sauna, or stack long sessions to chase a number. Dehydration is the entire mechanism behind that number, and it tends to make you feel worse, not leaner.
Alcohol, certain medications, and pregnancy all change how well you tolerate heat, so check with your clinician if any of those apply to you.
What a Sauna Can Reasonably Do for You
Research suggests regular sauna use may support relaxation, sleep, and recovery from hard training, and one of the studies above found lower blood pressure after sessions.4 We've written about the sleep angle in sauna for sleep and about session length in how long to stay in an infrared sauna. Those are good reasons to use one.
If weight is the goal, the levers with real evidence behind them are food, strength training, sleep, and for some people, medical treatment. A sauna fits fine on top of that routine as the part that feels good, as long as you don't expect it to do the work. For people exploring the medical side, our medical weight loss program in Lisle starts with a consultation that looks at labs, history, and what has and hasn't worked before. Tracking what is changing, fat versus fluid, is easier with a Styku 3D body scan than with a bathroom scale, and the post on DEXA vs 3D body scan vs InBody explains how the methods compare.
Sauna Sessions and Pricing at Defiant
Our sauna is a hybrid cabin at 5100 Lincoln Ave in Lisle, and it can run as either infrared or traditional dry heat. We see people from Naperville, Downers Grove, Wheaton, and Oak Brook. Sessions are $45 for 30 minutes, $65 for 45 minutes, and $85 for 60 minutes, and a first session for new clients is $25 for 30 minutes or $40 for 45 minutes. Sauna sessions are also included in the monthly credits on Defiant memberships.
If you want to stack it with cold, the contrast therapy page covers the guided sauna and cryotherapy option, and infrared sauna vs traditional sauna explains which heat setting to pick.
- The weight you lose in a sauna is mostly water. Studies measured about 0.5 to 0.65 kg lost per visit, and it comes back when you rehydrate.
- A 4-week, 12-session high-temperature sauna trial found no changes in weight and fat tissue versus a control group.
- Heart rate rose to roughly 136 bpm after 20 minutes in one study, but the verified studies did not report calorie burn.
- Larger bodies lose more fluid and also carry more heat strain, so more sweat is not a sign of a better session.
- Sauna may support relaxation, sleep, and recovery. Use food, strength training, and medical care for weight goals.
Frequently Asked Questions
Use the Sauna for What It's Good At.
Recovery, relaxation, and a warm reset after training. Book a session in our hybrid infrared and dry-heat cabin in Lisle, and track real change with a body composition scan instead of the bathroom scale.
Keep Reading
Last updated October 12, 2026.
References
- Boraczyński T, Boraczyński M, Podstawski R, Borysławski K, Jankowski K. Body mass loss in dry sauna and heart rate response to heat stress. Rev Bras Med Esporte. 2018;24(4):258-262. Full text
- Podstawski R, Borysławski K, Clark C, et al. Correlations between repeated use of dry sauna for 4 x 10 minutes, physiological parameters, anthropometric features and body composition in young sedentary and overweight men. Biomed Res Int. 2019;2019:7535140. PubMed
- Toro V, Siquier-Coll J, Bartolomé I, et al. Effects of twelve sessions of high-temperature sauna baths on body composition in healthy young men. Int J Environ Res Public Health. 2021;18(9):4458. PubMed
- Podstawski R, Bielec G, Borysławski K, Alföldi Z, Marzec A. Changes in the blood pressure, heart rate and body mass of physically active men in response to thermal stress. Cent Eur J Sport Sci Med. 2022;37(1):65-76. Full text