Rice cakes. Popcorn. Celery sticks. High-fiber crackers. Raw broccoli. They all fill up your stomach but contain very few calories. The volumetrics diet, for example, emphasizes eating lower-calorie, nutrient-dense foods such as fruits, vegetables, whole grains and low-fat dairy. However, this doesn't mean that you're guaranteed to eat less. Here's why: Fullness is not the same as satisfaction. These foods do a great job of physically filling up and stretching your stomach. But physically filling your stomach is only one part of your body's appetite regulation equation. The three macronutrients – protein, carbohydrates and fat – all play a role in triggering a cascade of events and hormones that signal to your body that you're done eating. If you're missing out on any of these food components, you may feel physically full for a short while, but soon after, you'll find yourself hungry again. So pick a carbohydrate, a protein and a fat at each meal.