Inadequate energy intake can be an important contributor to sarcopenia in older individuals, because negative energy balance induces negative nitrogen balance, independent of nitrogen intake. This review highlights recent studies from our laboratory on possible causes of negative energy balance in older individuals. Studies of energy requirements determined by measurement of total energy expenditure during weight maintenance, using the doubly labeled water technique, and the control of food intake following overeating and undereating indicate (a) that older individuals have higher energy requirements than anticipated, based on current Recommended Dietary Allowances for energy, and (b) that aging is associated with a significant impairment in the control of food intake, which inhibits appropriate compensation for prior changes in energy intake. The combination of unexpectedly high energy needs, and an inability to accurately control energy intake, increases the risk for negative energy balance and associated body fat and protein losses in older individuals.