Energy Expenditure in Older Adults Who Are Frail: A Doubly Labeled Water Study

Frailty is a common and important geriatric syndrome, distinct from any single chronic disease, and an independent predictor of mortality. It is characterized by age-associated decline in physiological reserve and function across multiple systems, culminating in a vicious cycle of altered energy expenditure. The total energy expenditure (TEE) of an individual includes the resting metabolic rate (RMR), the thermic effect of feeding, and the energy expenditure in physical activity (PAEE). The investigation of the energy expenditure of older adults who are frail is essential for better understanding the syndrome. Therefore, we compared the RMR, the PAEE, the physical activity level (PAL), and the TEE of older adults who were frail with those who were not frail.

A cross-sectional study was conducted with 26 community-dwelling older adults (66-86 years of age). Older adults in the frail and nonfrail groups were matched for age and gender, and the matched pairs were randomly selected to continue the study. The RMR was measured by indirect calorimetry. The TEE was obtained by the multipoint, doubly labeled water method. After collecting a baseline urine sample, each participant received an oral dose of doubly labeled water composed of deuterium oxide and oxygen-18 (H2O). Subsequently, urine samples were collected on the 1st, 2nd, 3rd, 7th, 12th, 13th, and 14th days after the baseline collection and analyzed by mass spectrometry.

The older adults who were frail presented significantly lower PAEE (1453.7 [1561.9] vs 3336.1 [1829.3] kj/d, P < .01), PAL (1.4 [0.3] vs 1.9 [0.6], P = .04), and TEE (7919.0 [2151.9] vs 10442.4 [2148.0] kj/d, P < .01) than the older adults who were nonfrail. There was no difference in their RMRs (5673.3 [1569.2] vs 6062.0 [1891.7] kj/d, P = .57). Frailty has been associated with a smaller lean body mass and with a disease-related hypermetabolic state, which might explain the lack of difference in the RMR. The PAL of the older adults who were frail was below the recommended level for older adults and determined a lower PAEE and TEE when compared with older adults who were not frail.

This study showed that low energy expenditure in physical activity is a main component of frailty. The PAL of the older adults who were frail was far below the recommended level for older adults.