Protein is essential for maintaining the lean body mass (muscle) in humans. In adults, for example, the normal dietary intake for protein (containing the essential (cannot be made by the body) and non-essential amino acids) is approximately 0.8 g per kilogram of body weight (1 kg = 2.2 lbs), but during acute illness, requirements double to approximately 1.5 g/kg. Thus, in the patient weighing 70 kg (or 154 lbs), they would receive approximately 100 grams of protein. If therapy is provided by a catheter into the stomach or intestine, whole or complex proteins such as from milk sources are used, whereas if therapy is provided by an intravenous catheter, the protein source is in a simplified form as crystalline amino acids. Protein intake during acute illness, however, may be modified according to various clinical factors such as: 1) the patient's weight in relation to standard tables showing the normal body mass index according to the World Health Organization; 2) impairments in kidney or liver function; 3) blood levels of various nutrients for metabolic control.