The Atwater energy equivalents of 16.7, 16.7 and 37.7 kJ/g of protein, carbohydrate and fat, respectively, are the standard values used to calculate the macronutrient intakes required to meet a person's metabolizable energy requirement. The aim of this study was to compare in older people the measured metabolizable energy intake (MEI(MEAS)) required to achieve and maintain stable body weights with the MEI estimated using the Atwater energy equivalents (MEI(AT)). During a 96-d (14-wk) strictly controlled dietary period, 11 men and 17 women (55-78 y old) were each provided a MEI(AT) to maintain body weight within +/- 0.5 kg of baseline weight. The MEI(MEAS) was determined retrospectively from the gross energy contents of food, urine and feces samples collected during week 14. Resting energy expenditure was measured using indirect calorimetry. At wk 14, MEI(AT) overestimated MEI(MEAS) by 26%. These results suggest that the Atwater energy equivalent values may overestimate the actual MEI of older people.