BBC Science Focus
WHY DO I HAVE LESS OF AN APPETITE IN HOT WEATHER?
All of our metabolic processes generate heat, including digestion. For every 1,000 calories you eat, only 250 are converted into useful energy – the rest ends up as waste heat. In hot weather, your body is already working hard to keep you from overheating, and it doesn’t need the extra heat from digesting a big dinner. So your appetite is temporarily dialled back and your body gets more of its energy from stored fat reserves instead.