The dry sauna is a hot, low-humidity environment where temperatures typically range from 150°F to 195°F. Many people are drawn to this practice with the hope of passively increasing their energy expenditure. The energy used during a session is a direct result of the body’s effort to regulate its core temperature, which requires metabolic work.
Caloric Expenditure in a Dry Sauna
The number of calories burned in a dry sauna varies significantly based on individual factors and the intensity of the session. For an average 150-pound adult, a 30-minute session may burn approximately 90 to 150 calories more than what would be burned while simply resting outside the sauna. This represents the additional energy expenditure beyond the Basal Metabolic Rate (BMR), which is the energy required to maintain basic body functions at rest.
To put this in perspective, this extra burn rate is comparable to the energy used during light activities such as a slow walk or leisurely stretching. The exact caloric output is highly dependent on the sauna’s temperature and the duration of the exposure. Higher temperatures force the body to work harder to cool itself, thereby consuming more energy.
An individual’s body mass and existing metabolic rate are also major variables that influence the final calorie count. Larger individuals generally expend more energy because their body must work harder to cool a greater surface area and mass. Studies have shown a wide range of results, from a marginal 30 calories to over 200 calories in a 30-minute period, underscoring the importance of these personal differences.
Physiological Response to Heat Stress
The mechanism behind the energy expenditure is the body’s attempt to maintain a stable internal temperature, a process known as thermoregulation. When exposed to extreme heat, the body initiates physiological responses to prevent overheating, which requires energy supplied by burning calories.
The most noticeable change is a significant increase in heart rate, which can rise by 50% to 75%, mimicking the cardiovascular response to moderate exercise. This increased heart rate is necessary to pump blood rapidly toward the skin’s surface, a process called vasodilation, where heat can be dissipated. Simultaneously, the sympathetic nervous system is activated, releasing hormones like epinephrine.
These hormonal and cardiovascular adjustments elevate the body’s metabolic demand as it actively attempts to cool down. The body’s cooling system is effectively working overtime, and this increased internal workload is what accounts for the modest rise in calorie consumption. This heat-induced metabolic effort is a form of non-exercise activity thermogenesis (NEAT).
Water Loss Versus Fat Loss
The rapid, noticeable drop in weight immediately following a dry sauna session is nearly all due to fluid loss, not the burning of fat. The body’s primary cooling method in the sauna is the production of sweat, which is mostly water pulled from the bloodstream and tissues. Losing a liter of sweat, for example, results in a temporary weight reduction of about two pounds.
This fluid loss is temporary, and this weight is quickly restored once a person rehydrates by drinking water. True, sustained weight loss only occurs when the body metabolizes stored fat or glucose to create a long-term caloric deficit.
The calories burned in the sauna contribute only a small fraction to a person’s total daily energy expenditure. Therefore, while a sauna session may support overall wellness and recovery, it is not a substitution for regular exercise and dietary management for achieving fat loss. The focus must remain on replacing the lost fluids to prevent dehydration and maintain normal bodily functions.