Frailty in Older Adults: Evidence for a Phenotype

No current treatment for obesity reliably sustains weight loss, perhaps because compensatory metabolic processes resist the maintenance of the altered body weight. We examined the effects of experimental perturbations of body weight on energy expenditure to determine whether they lead to metabolic changes and whether obese subjects and those who have never been obese respond similarly. We repeatedly measured 24-hour total energy expenditure, resting and nonresting energy expenditure, and the thermic effect of feeding in 18 obese subjects and 23 subjects who had never been obese. The subjects were studied at their usual body weight and after losing 10 to 20 percent of their body weight by underfeeding or gaining 10 percent by overfeeding. Maintenance of a body weight at a level 10 percent or more below the initial weight was associated with a mean (+/- SD) reduction in total energy expenditure of 6 +/- 3 kcal per kilogram of fat-free mass per day in the subjects who had never been obese (P < 0.001) and 8 +/- 5 kcal per kilogram per day in the obese subjects (P < 0.001). Resting energy expenditure and nonresting energy expenditure each decreased 3 to 4 kcal per kilogram of fat-free mass per day in both groups of subjects. Maintenance of body weight at a level 10 percent above the usual weight was associated with an increase in total energy expenditure of 9 +/- 7 kcal per kilogram of fat-free mass per day in the subjects who had never been obese (P < 0.001) and 8 +/- 4 kcal per kilogram per day in the obese subjects (P < 0.001). The thermic effect of feeding and nonresting energy expenditure increased by approximately 1 to 2 and 8 to 9 kcal per kilogram of fat-free mass per day, respectively, after weight gain. These changes in energy expenditure were not related to the degree of adiposity or the sex of the subjects. Maintenance of a reduced or elevated body weight is associated with compensatory changes in energy expenditure, which oppose the maintenance of a body weight that is different from the usual weight. These compensatory changes may account for the poor long-term efficacy of treatments for obesity.

1. Residents of a chronic care hospital (13 men of mean age 88.5 +/- 6 SD years and 13 women of mean age 86.5 +/- 6 SD years) who had multiple pathologies were assessed for leg extensor capability in several ways. 2. A custom-built rig was used to assess leg extensor power, that is, maximal power output over less than 1 s in a single extension of one leg. Performance measures were obtained by timing chair rises (from a standard chair 0.43 m high), stair climbing (four risers, total height 0.635 m) and a walk (6.1 m). For each measurement the best of several trials were recorded as definitive. 3. Leg extensor power was significantly correlated with all performance measures, but the performance measures were not related to each other except for chair rising and walking speed. 4. Women had significantly less extensor power than men, but their power explained more of the variance in performance, e.g. power accounted for 86% of the variance in walking speed. 5. There was no relation within the group between age and any of the variables measured. 6. Measurement of leg extensor power in frail elderly people may prove useful in focusing effective rehabilitation programmes.