Is severe wasting in elderly mental patients caused by an excessive energy requirement?

Many chronically ill mental patients show rapid and severe weight loss leading to severe nutritional debilitation. Excessive energy requirements secondary to hypermetabolism or hyperactivity have been proposed as the cause. This hypothesis was tested using the new doubly-labelled water (2H218O) technique to obtain accurate estimates of total energy expenditure (TEE) in 14 such patients. Mean TEE was very low (6.1 +/- 1.3 MJ/day). None of the subjects was in significant negative energy balance when studied. Mean resting metabolic rate (RMR) was lower than predicted from standard equations based on healthy elderly subjects. The energy cost of physical activity plus thermogenesis was also low (1.7 +/- 0.9 MJ/day) in all except one subject. The data refute the initial hypothesis and suggest that negative energy balance may be episodic, perhaps during periods of infection and subsequent recovery.