Using a protein shake as an occasional meal replacement may help you lose more weight and fat than you would by following a reduced-calorie diet. According to the “American Journal of Clinical Nutrition,” high-quality proteins are more satiating than either carbohydrates or fats, and they may have the ability to improve the body’s metabolism. Additionally, a study that appeared in the journal “Nutrition & Metabolism” in 2008 stated that obese women and men lost more fat when they drank two protein shake meal replacements per day and followed a low-calorie diet. Subjects who adhered to the diet without the shakes lost less total body fat and more lean muscle mass. The study did not take nutrient deficiencies or diet balance into account, however. Unless you have approval from your doctor, do not replace more than one meal daily with a protein shake.