Does Sweating Burn Fat? What the Evidence Says
Does sweating burn fat? Learn why the amount you sweat doesn't measure fat burned, what sweat is made of, and where lost fat actually goes.
The 30-second summary
- Sweat is how your body cools down. It is mostly water and salt, so how much you sweat doesn't tell you how much fat you burned.
- A 2025 systematic review of 43 studies found hot yoga raised body temperature and heart rate, but not energy burned, compared with non-heated yoga.
- Most of the direct evidence comes from hot yoga studies in which 76% of participants were women, so it may not apply equally to every sport or person.
Does sweating burn fat? The short answer is no. Sweat is your body's way of getting rid of heat, and it is mostly water and salt. You can sweat a lot simply because the room is hot, without burning more energy. So the amount you sweat is not a measure of the fat you burned.
Below, we look at why so many people link sweat with fat burning, what a recent review of hot yoga found, and where fat actually goes when you lose it. We also answer two common questions: does sweating make you lose weight, and what is sweating during exercise good for?
The popular claim
«The more you sweat, the more fat you burn»
Myth
Sweat is your body's cooling system and is mostly water and salt. How much you sweat reflects the heat from your working body and your surroundings, not how much fat you burned.
Why do people believe it?
The idea feels logical. The harder you exercise, the more heat your body makes, and the more you sweat. A 2019 review by Baker notes that the body gains heat mainly from two sources: its own work during exercise and the surrounding environment. So sweat often goes along with harder workouts, which makes it look like a sign of burning.
Seeing how much fluid you lose adds to the belief. In 90 minutes of Bikram yoga, a type of hot yoga, people lost 1.5 litres of sweat on average and drank only about 0.4 litres, roughly a quarter of what they lost. Hot sessions may also feel harder, but feeling more effort is not the same as burning more energy.
What does the evidence say?
The most direct evidence comes from a 2025 systematic review by Willmott and colleagues in Sports Medicine - Open. It gathered 43 studies on hot yoga with 942 participants, 76% of them women. A single hot yoga session raised body temperature and heart rate, but not the energy the body used, compared with non-heated yoga. The authors concluded that hot yoga does not consistently or meaningfully raise energy burned or oxygen use, although people may feel they are working harder.
On what sweat actually is, a 2019 review by Baker in the journal Temperature says the main job of sweating is to release heat and control body temperature. Sweat is a complex mix, but mostly water and sodium chloride (table salt), along with many other substances. The main things that decide how much you sweat are the heat your body makes during exercise, which rises with effort, and the heat around you.
And the fat itself? Research by Meerman and Brown in the BMJ, explained by UNSW Sydney in 2014, followed what happens to fat when it is lost. Of every 10 kg of fat, 8.4 kg leaves through the lungs as carbon dioxide, and 1.6 kg becomes water that exits in urine, faeces, sweat, breath, tears and other fluids. So sweat is one of several exits for a small part of it, not the main route. The researchers also point out that breathing more than your body needs does not cause weight loss.
We rate evidence by study design, not by how exciting the result is. How we rate evidence
The takeaway
Don't judge a workout by how much you sweat, and replace the fluids you lose by drinking water.
But keep in mind
- The clearest comparison of exercising in the heat versus without it comes from hot yoga studies; the review did not test every type of exercise.
- Women made up 76% of the 942 participants across the 43 studies, so the results may not represent everyone equally.
- The review says hot yoga does not raise energy burned 'consistently or meaningfully', which suggests the studies did not all find exactly the same thing.
- The 1.5-litre figure is an average from 90-minute hot yoga sessions and varies between people. In general, how much you sweat depends on effort, the heat around you and body size.
FAQ
Is sweating during exercise a sign of burning fat?
Not a reliable one. Harder exercise makes more heat, so you sweat more, but a hot room makes you sweat more too. In hot yoga, body temperature and heart rate went up without a rise in energy burned compared with non-heated yoga.
Does sweating make you lose weight?
You can lose a lot of fluid through sweat: about 1.5 litres on average in 90 minutes of hot yoga. But what you lose is mostly water and salt, not fat, so replace it by drinking water.
What is sweating during exercise good for?
Its main job is to release heat so your body temperature stays in check. You sweat more as exercise gets harder or your surroundings get hotter, and people with a larger body sweat more because they make more heat for the same work.
Where does fat go when you burn it?
According to research by Meerman and Brown in the BMJ, explained by UNSW Sydney in 2014, of every 10 kg of fat lost, 8.4 kg is breathed out as carbon dioxide. The other 1.6 kg becomes water that leaves in urine, faeces, sweat, breath, tears and other body fluids.
Sources
- 1Hot Yoga: A Systematic Review of the Physiological, Functional and Psychological Responses and AdaptationsSports Medicine - Open (Willmott et al.) · 2025
- 2Physiology of sweat gland function: The roles of sweating and sweat composition in human healthTemperature (Baker LB) · 2019
- 3When we lose weight, where does the fat go?UNSW Sydney Newsroom (on Meerman & Brown, BMJ) · 2014
These are the original sources; we only explain them. Read them yourself.
Science information for education only; it does not replace medical advice.
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