The retrieved sources uniformly support the claim's core content. An exercise physiologist is quoted stating that sweating is not a reliable indicator of fat oxidation or energy expenditure and is merely the body's cooling mechanism , and that sweat volume can vary due to heat and humidity, clothing, hydration level, and individual differences in sweat rate, while high-intensity workouts that make you sweat heavily can burn many calories, the sweat itself is not the cause . A pharmaceutical technical director quoted in Business Standard called the assumption that sweating is directly proportional to fat burn a myth, explaining that fat breakdown depends on calorie expenditure and metabolic activity , and that heavy sweating during exercise does not always indicate higher fat burn . Consumer explainers state directly that sweat is not melted fat leaving the body but the body's cooling system . Sources also note that a person can burn fat and calories effectively while sweating little, for example in a cool room .

Background context from training knowledge, not a retrieved source: fat oxidation ends in carbon dioxide exhaled through the lungs and water excreted through urine, sweat and breath, so the fat itself is not lost as sweat. Sweat is essentially water with dissolved electrolytes, chiefly sodium and chloride. Acute body mass drops after sweaty exercise are dominated by fluid loss and are reversed by rehydration. This is the basis of the rapid "weight cut" practiced by weight-class athletes, which does not reflect fat loss.