Total energy expenditure in the elderly.

Chronic diseases and disabilities increase with age, affecting more than 60% of those over 75 y, and limiting activities in about half of them. Therefore, total energy expenditure (TEE) and its components are assessed separately in health and disease. An analysis of 568 doubly labelled water measurements in 'healthy' subjects (184 measurements in subjects over 65 years) suggests that there is a decrease of 0.69 and 0.43 MJ/day/decade respectively in men (standard weight 75 kg) and women (standard weight 67 kg). Physical activity (PA) accounted for 46% of the decrease in TEE, basal metabolic rate (BMR) for 44% of the decrease and thermogenesis (T) for the remaining 10%. TEE was found to be 10.79+/-2.09 and 8.62+/-1.49 MJ/day in 150 men and 100 women aged over 60 y, respectively. Of the total variance in TEE, measured with doubly labelled water over a 2 week period, 69% was considered to be due to differences between individuals, and 31% to differences within individuals. The variance due to PA plus T was threefold greater than that due to BMR. Physiological factors were far more important than methodological factors in influencing measurements of TEE, BMR and PA+T. An analysis of 136 measurements of TEE (doubly labelled water and bicarbonate-urea methods) in free-living elderly patients suffering from a variety of diseases suggests a frequent decrease in TEE, which may occur despite an increase in BMR. This is largely due to a reduction is PA (eg up to approximately 50% reduction), but in some cases it is also due to a reduction in BMR (loss of body weight). More comprehensive information is required about TEE and its components, partly because of a probable selection bias in recruitment of subjects participating in specific tracer studies, and partly because of the variable effects of different diseases and factors that operate at different times in the course of the same disease.