Minecraft wiki entry for Beginner%27s_guide, associated text: If you get too hungry, you start suffering: Below 90% you can't heal damage, below 30% you can't sprint, and if the hunger bar goes empty, you'll lose health to starvation. You can't actually starve to death unless you're in Hard difficulty, but you are still quite vulnerable. You do not lose hunger at all in Peaceful mode. See the Second Day guide for slightly more detail, or the Hunger page for the whole story.