A lot of the time it's hard to distinguish between real physical hunger and mental or emotional hunger. One of the biggest causes of weight gain is emotional eating, which happens anytime you eat for reasons other than physical needs. It's surprisingly easy to convince yourself that you're hungry when your body doesn't actually need food. Therefore, use the following tests before eating anything to determine whether you are about to eat emotionally or because your body actually needs the nourishment.
First and foremost, pay attention to the hunger scale. Your goal is to stay between four and eight at all times. The first test is simply to check in with your body and consciously register where you're at on the hunger scale. If you're at a five or a six, you probably don't need to eat anything right now.
Apple Test: before you eat, ask yourself if you would still want it if it were only an apple (or some other fruit or vegetable that you like but are not tempted to overeat). If the answer is yes, why not go for that apple (or other fruit or vegetable) to truly nourish that physical hunger? If the answer is no, then the hunger/craving you are experiencing is probably not a physical hunger in your stomach, but instead an emotional hunger.
Water Test: drink a glass or two of water before you eat. Your perception of your hunger signals might actually be thirst signals.