Protein-rich foods can also suppress levels of the hormone ghrelin — the one released when our stomach is empty to make you hungry — they help create a long-lasting feeling of fullness. Try adding whey protein to a low-calorie smoothie. (If you're sensitive to gluten, just be sure to check the ingredients list; some whey protein products contain gluten.) One study found that whey brought about a prolonged suppression of ghrelin.