 When it's really hot, why does it appear that our appetite is reduced when we're feeling so warm? Yeah, I know. It's interesting, isn't it? So it's been scientifically proven that when our core body temperature rises, and of course, that's what happens when we get really hot weather, our appetite declines. And this means that anything that increases core body temperature can affect appetite. And so that includes exercise, as well as the steamy weather that we often have in the summer, or even if you have a fever.