Know it: The number of calories per serving is usually the first thing people read when they look at a food label. But beware: The USDA allows manufactures to use an estimate that can be up to 20-percent off! And because the serving size is a minimum amount rather than an exact amount, it's more likely that the food has more calories per serving than the label leads you to believe.
Avoid it: If you're being very conscious of calories, some nutritionists recommend automatically adding 10 percent as a buffer and carefully weighing and measuring your food. A more reasonable approach: Listen carefully to your sense of fullness and stop eating when you're satisfied—even if you haven't finished a whole serving.