The average adult needs 1 to 2 g protein/kg of body weight and 25 to 30 kcal/kg of body weight per day. Caloric needs in adults differ based on height, weight, activity level, and disease state. Malnutrition is defined as an imbalance of nutrition, including lack of adequate calories, protein, and/or other nutrients required for body functioning. Protein-calorie malnutrition is a specific type of malnutrition defined as deficient intake or uptake of protein and energy that leads to physiologic alterations such as inflammation, loss in fat-free mass, and/or decreased response to medical treatment. Worldwide, 20% to 50% of hospitalized patients have malnutrition preadmission, and up to 90% of older adult patients are at increased risk. All patients should be screened for malnutrition within 24 hours of hospital admission. If malnutrition is suspected in the outpatient setting, patients should be screened with assistance from a registered dietitian nutritionist. The treatment strategy for protein and calorie supplementation involves provision of additional calories via oral nutritional supplements, enteral tube feedings, or parenteral nutrition. Oral nutritional supplements are indicated for patients with mild cases of malnutrition who are able to consume food orally. Meal replacement products are a convenient way to modify macronutrient intake, including use as a temporary solution to increase intake in patients with malnutrition and as an intervention for weight loss.