The accuracy of predictive equations for calculating resting energy expenditure (REE) in elderly people has been questioned. Aging is associated with progressive declines in REE, which partly is explained by loss of fat free mass (FFM). Against this background we aimed to identify the most accurate predictive equation for REE in octogenarian men, taking body composition into account and using indirect calorimetry as reference value. REE was measured in 22 men (mean age 82.6±0.3years) and compared with six predictive equations: two based on FFM and four based on body weight, height and/or age. FFM was derived from Dual-energy X-ray absorptiometry analyses. Spearman's rank correlations showed a moderate to high positive monotonic correlation (r=0.62 to 0.79) between measured and calculated REE (all p