Appetite decreases with heat partly because the body is trying to keep cool. All of the body's functions, including digestion, create heat within the body. A body working hard to keep cool will suppress appetite in an attempt to lessen its work load. Additionally, with heat comes perspiration. You not only lose water when you perspire, you lose vitamins and minerals. The loss of vitamins and minerals can contribute to chemical imbalances within the body that can suppress appetite.