The experience of sitting in a sauna, which involves exposure to high heat, often leads to a noticeable drop on the scale immediately afterward. Traditional saunas heat the air to temperatures between 150°F and 195°F, while infrared saunas use light waves to warm the body directly. This intense thermal environment forces the body to work hard to maintain its core temperature, resulting in temporary weight change due to fluid loss through heavy sweating.
The Immediate Weight Loss Result
A single, one-hour session in a sauna can result in a temporary weight loss ranging from approximately one to five pounds. This figure is variable, influenced by individual factors like starting hydration level, total body mass, and sweat rate.
The type of sauna also plays a role, as does the temperature setting and session duration. This immediate result is a measurement of mass lost, not a measure of permanent body change.
How Saunas Induce Temporary Weight Reduction
The physiological process causing this temporary weight reduction is the body’s attempt at thermoregulation. When exposed to the heat, the body must prevent its core temperature from rising. This leads to an increase in heart rate, similar to moderate physical activity.
The primary cooling mechanism is the production of sweat, which is composed of about 99% water. The profuse sweating expels a significant volume of this fluid from the body. This rapid loss of water mass registers as a lower number on the scale immediately following the session.
The Critical Difference Between Water Weight and Fat Loss
The weight reduction achieved in a sauna is almost entirely water weight, which has no lasting impact on body composition. Sustainable weight loss requires achieving a caloric deficit, meaning more calories are burned than consumed. Fat loss occurs when the body breaks down stored adipose tissue for energy.
The minimal increase in metabolic rate caused by heat stress does not equate to the substantial caloric expenditure needed to burn significant fat. The small number of calories burned while sitting is negligible compared to the deficit required for meaningful fat loss. This temporary fluid loss is quickly reversed once the individual rehydrates.
Safe Sauna Use and Hydration Guidelines
Given the rapid fluid loss, safety and proper hydration must be the focus of any sauna session. For most healthy adults, sessions should not exceed 15 to 20 minutes; a full 60-minute session is strongly discouraged due to the extreme risk of dehydration and overheating. New users should begin with shorter durations, around five to ten minutes, to assess tolerance.
It is advised to drink sufficient water before entering the sauna. After exiting, the lost fluid must be replaced immediately, and water intake should be two to four glasses to restore hydration balance. For extended or frequent use, incorporating an electrolyte-containing beverage helps replenish lost sodium and potassium.
Users should be aware of the warning signs of overheating, including dizziness, nausea, lightheadedness, and an intense headache. If any of these symptoms occur, the session must be ended immediately, and the person should move to a cooler environment. Consuming alcohol before or during a sauna session is highly dangerous, as it accelerates dehydration and impairs the body’s ability to regulate its temperature.