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Limited evidenceMyth check

Sweating more means burning more fat

Sweat is water and electrolytes, not fat. The weight you lose in a sweaty session, sauna or plastic suit is fluid that returns as soon as you drink. How much you sweat mostly reflects heat, humidity, clothing, body size and heat acclimatisation, not how much fat you burned.

What the science says

  • The scale drop after a sweaty workout is fat Limited evidence

    The ACSM's 2007 position stand on exercise and fluid replacement (Sawka and colleagues) treats the change in body weight before and after exercise as a measure of sweat loss, i.e. water, and recommends replacing it afterwards. That short-term weight loss is fluid and is regained with rehydration.

  • Sweat is mostly water and salts Moderate evidence

    Baker's 2019 review of sweat gland physiology describes sweat as a water-based fluid whose main job is cooling the body through evaporation; its solutes are mainly sodium chloride and other electrolytes. Fat is not excreted in sweat: it is used up in metabolism.

  • Sweating more means working harder or detoxing Limited evidence

    Baker's review notes that sweat rates vary widely between people and rise with heat acclimatisation, and that the role of sweat in eliminating waste products or toxins appears minor compared with the kidneys and gut. Sweat volume is a poor guide to energy expenditure.

What to do instead

Judge fat loss by trends in body weight and waist measurements over weeks, created by an energy deficit, and replace the fluid you sweat out.

What drives fat lossA sustained calorie deficit plus regular training
TrackingWeekly average body weight and waist, not pre- vs post-workout weight
Fluid replacementDrink to replace sweat losses; avoid losing more than about 2% of body weight during exercise
Saunas and sweat suitsFine for comfort or heat tolerance, useless for fat loss
Estimating your sweat rateWeigh yourself before and after a session (adjusting for drinks)

Who should be careful

Deliberate dehydration (sweat suits, saunas, fluid restriction to 'make weight') can be dangerous, especially in heat. People with heart or kidney conditions, or who are pregnant, should ask a physician before heat exposure or heavy-sweating exercise.

Frequently asked questions

Why do I weigh less right after a sweaty workout?

Because you lost water. The ACSM uses that before-after weight change to estimate sweat loss and recommends replacing it.

Does sweating flush out toxins?

A 2019 review found the role of sweat in eliminating waste products or toxins is minor compared with the kidneys and gut.

Do people who sweat more burn more fat?

Not necessarily. Sweat rates vary widely between people and increase with heat acclimatisation; sweat volume is a poor guide to energy expenditure.

Scientific references

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