Your body primarily uses carbohydrates for fuel. But when those run out—like, say, during a hard workout—your protein stores get burned up, producing ammonia as a byproduct, which is excreted in your sweat. A low-carb, high-protein diet speeds the build up of ammonia. Dehydration makes it even worse because there’s less water to dilute the stinky stuff. If you notice an ammonia stench when you sweat, make sure to drink lots of water, and up your carb quotient before you exercise.