Your body's telling you that you need specific nutrients. Maybe you feel run down, and feel you need a hamburger (protein). Or perhaps the need for some quick energy from carbohydrates after a game of volleyball or tennis is calling you. Or maybe, if less likely, you crave liver (you may be needing iron). Listen to these signals. They're another example of God's profoundly beautiful design of our human bodies.
The only catch is that many of us also hear habits talking. Voices like "I want ice cream." Or perhaps you drive by a donut shop and think you must have one, or a dozen! Or sometimes (like me) you think you need a cup of coffee to get through the day. (When what I really need is a nap!)
A good way of determining whether it's body cravings or habits is to try to develop a sense of where those feelings are coming from. If they’re coming from your stomach, bowels, or torso--then you're likely noticing a really important craving. If they’re coming from your head, then you're probably hearing from a habit. Also, if your second thought is something like: "Gosh, I don't really need donuts or ice cream," pay attention. Let your conscience guide you as well.