This review briefly examines the effects of aging on resting metabolic rate, thermic effect of a meal, and the energy expenditure of physical activity. Thereafter, the effects of advancing age on total daily energy expenditure as assessed from doubly labeled water studies are examined. The paucity of studies in this area and the small sample sizes preclude definitive conclusions regarding daily energy requirements in the elderly. The rationale underlying measurement of daily energy expenditure to determine energy requirements in older individuals is presented. Evidence is provided that older individuals frequently underreport daily energy intake, and this underreporting is more pronounced in older women with higher levels of body fat. The effects of aerobic and resistance training on resting metabolic rate and total daily energy expenditure are then examined. Both forms of training increase resting metabolic rate due to increases in sympathetic nervous system activity. Lastly, procedures to normalize body size dependent data are discussed. © 1996 Wiley-Liss, Inc.