Does sweating more burn more fat?
Short answerNo
No. Sweat is about 99% water, and it’s how your body cools down. The pound or two you lose in a sweaty workout or a sauna is water, and it comes back as soon as you drink. Fat leaves your body mostly as carbon dioxide you breathe out, and how much leaves depends on the calories you burn, not the sweat.
What we’d do
Judge a workout by what you did, not by how wet your shirt is. Skip sauna suits and wraps sold for fat loss. If you sweat a lot, weigh yourself before and after a long workout and drink to replace what you lost. Enjoy a sauna for how it feels, not for fat loss.
If you remember three things
- Sweat is water, and the weight it takes comes back when you drink.
- Fat leaves mostly through your lungs, as carbon dioxide.
- Heat makes you sweat, not burn fat. Hot rooms and sweat suits change the sweat, not the fat.
Why it seems true
Sweat feels like effort leaving the body. You step on the scale after a hot class and you’re a pound or two lighter, which looks like proof. Sauna suits, belly wraps and hot yoga have all been sold on that feeling.
The scale is right that you weigh less. It just can’t tell you what you lost. Sports scientists use exactly that drop to measure how much water someone sweated out: weigh before, weigh after, and the difference is the fluid to replace.
Judging a workout by sweat is like judging a car’s mileage by how hot the engine runs. The heat tells you about the weather and the cooling, not the distance.
What sweat is
Sweat from the glands that cool your skin is about 99% water, with a little salt. It evaporates and carries heat away. How much you sweat varies from person to person and day to day, which is why the American College of Sports Medicine suggests weighing before and after exercise to estimate it.
A sauna shows how much water it can be. Harvard Health puts it at about a pint for an average person in a short sauna session. A pint of water weighs about a pound, and all of it is water you’ll drink back.
Where fat goes
When your body burns fat for energy, it breaks it into carbon dioxide and water. In 2014, two scientists at UNSW Sydney worked out the chemistry: of 10 pounds of fat burned, about 8.4 pounds leave through your lungs as carbon dioxide and 1.6 pounds become water. So the main exit for fat is your breath, and it only opens when your body burns more energy than you eat. See where does fat go when you lose it.
How to use the scale after a sweaty workout
The drop on the scale is useful, just not for fat. Weigh yourself before and after a long or hot session, in the same clothes. The difference is roughly the water you lost, and the American College of Sports Medicine advises replacing that fluid afterward. If you’re down two pounds after a class, that’s about two pounds of water to drink back over the next hours. Your fat loss shows up in the weekly average of your morning weigh-ins, weeks later.
More detail: why heat doesn’t burn more fat
A hard workout in the heat does burn calories, but they come from the work, not the heat. Exercise on its own takes off modest amounts of fat: in a 2017 review of 31 trials, people lost about 2 to 3 pounds (0.9 to 1.4 kg) of fat on average over weeks of cardio. Turning up the heat changes the sweat and the risk of getting dehydrated, which can make the session harder to finish.
6 sources
- Cleveland Clinic, Sweatmy.clevelandclinic.org
- Sawka et al., American College of Sports Medicine position stand: exercise and fluid replacement, Medicine and Science in Sports and Exercise, 2007pubmed.ncbi.nlm.nih.gov
- Harvard Health Publishing, Sauna health benefits: are saunas healthy or harmful?harvardhealth.org
- Meerman and Brown, When somebody loses weight, where does the fat go?, BMJ, 2014pubmed.ncbi.nlm.nih.gov
- UNSW Sydney, When we lose weight, where does the fat go?, news release on Meerman and Brown, 2014unsw.edu.au
- Keating et al., A systematic review and meta-analysis of interval training versus moderate-intensity continuous training on body adiposity, Obesity Reviews, 2017pubmed.ncbi.nlm.nih.gov
