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. Theref ore, total energy expenditure (TEE) and its components are assessed separat ely in health and disease. An analysis of 568 doubly labelled water measure ments in 'healthy' subjects (184 measurements in subjects over 65 years) su ggests 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 ra te (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 a nd 100 women aged over 60 y, respectively. Of the total variance in TEE, me asured 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 methodologi cal factors in influencing measurements of TEE, BMR and PA+T. An analysis o f 136 measurements of TEE (doubly labelled water and bicarbonate-urea metho ds) in free-living elderly patients suffering from a variety of diseases su ggests a frequent decrease in TEE, which may occur despite an increase in B MR. This is largely due to a reduction is PA (eg up to similar to 50% reduc tion), 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 comp onents, partly because of a probable selection bias in recruitment of subje cts participating in specific tracer studies, and partly because of the var iable effects of different diseases and factors that operate at different t imes in the course of the same disease.