I was in the gym doing bent over rows and to my left I heard a gym rat telling a newbie that it is important to sweat because sweating actually burns fat. The guy had an incredible physique, but I have to see his knowledge about the metabolic functions of the human body are tad bit to the ignorant side of things. I’d say his statement was akin to the tail wagging the dog.
Sweating is a response of our autonomic nervous system when the temperature of our bodies (due to increased exercise or just hot weather) begins to rise. Our pores release sweat so that it can evaporate. The evaporation process requires energy to convert water molecules into humidity in the air. Because energy is taken from the heat surrounding the water to facilitate this process, the heat (the energy) on the skin is reduced — hence a natural refrigeration process.
So it is not the sweating that is burning the fat. Sweating is in response to the increase in body temperature. But if that increase in body temperature is due to exercise, then that temperature increase is due to a metabolic increase. And yes, the metabolic increase does burn fat (especially if the exercise is slow and steady.)
So does sweating burn fat? No, but it may be the result of an activity that is burning fat. So laying on the beach in the sun sweating is probably not doing much for your waistline. However, if that sweat is earned with exercise that it is a touchstone that your metabolism is attacking those nasty little fat cells.