Resting Metabolic Rate in Old-Old Women with and without Frailty: Variability and Estimation of Energy Requirements

Objectives To measure resting metabolic rate (RMR) in old-old adults living in the community and examine the association between measured RMR and frailty status and compare it with expected RMR generated by a predictive equation. Design Physiological substudy conducted as a home visit within an observational cohort study. Setting Baltimore City and County, Maryland. Participants Seventy-seven women aged 83 to 93 enrolled in the Women's Health and Aging Study II. Measurements Resting metabolic rate with indirect calorimetry, frailty status, fat-free mass, ambient and body temperature, expected RMR according to the Mifflin-St. Jeor equation. Results Average RMR was 1,119 +/- 205 kcal/d (range 5951,560 kcal/d). Agreement between observed and expected RMR was biased and poor (between-subject coefficient of variation 38.0%, 95% confidence interval = 35.140.8). Variability of RMR was greater in frail individuals (heteroscedasticity F-test P = .02). Low and high RMR were associated with being frail (odds ratio 5.4, P = .04) and slower self-selected walking speed (P < .001) after adjustment for covariates. Conclusion Equations to predict RMR that are not validated in old-old adults appear to correlate poorly with measured RMR. RMR is highly variable in old-old women, with deviations from the mean predicting clinical frailty. These exploratory findings suggest a pathway to clinical frailty through high or low RMR.