Meal replacements are pre-packaged meals intended to make it easier and more efficient for an individual to control his or her portion sizes when trying to lose weight. They are available over-the-counter and are typically fortified with vitamins and minerals, and contain around 300 calories or less per serving.

Many times consumers classify foods as good or bad, healthy or unhealthy, or allowed or forbidden. Instead of classifying foods into positive or negative categories, try evaluating them based on nutrient density. Nutrient density refers to the amount of nutrients for the given volume of food; in other words, containing the most nutrition per bite. The opposite of nutrient density is energy density. By definition energy dense foods have more calories per volume and provide few nutrients.