Diminished meal-induced thermogenesis in elderly man.

The purpose of this study was to examine the possible influence of age on thermogenic response to a mixed meal in healthy subjects. Twenty-five healthy male subjects participated in the study and they were divided into three groups, comprising 10 young subjects with an average age of 27 years (22-35 years), seven middle-aged individuals (51 years, 42-60 years) and eight elderly men (70 years, 67-74 years). They were all studied with continuous indirect calorimetry in the basal state and for 3 h after the ingestion of a mixed meal in liquid form. The size of the meal corresponded to 60% of the individually computed 24-h basal energy expenditure. Resting energy expenditure was lower in the elderly men than in the young ones when expressed in absolute values (P less than 0.001) as well as in relation to body weight (P less than 0.01) and body surface area (P less than 0.01). After the meal energy expenditure increased rapidly and reached a relatively constant level after 60 min in all groups; the average increase above the basal level during the whole postprandial period was less in the elderly (21.1 +/- 2.5%, P less than 0.01) and the middle-aged (24.2 +/- 1.7%, P less than 0.05) than in the young (28.6 +/- 1.6%) men. It is concluded that the thermogenic response during the first 3 h following a mixed meal decreases with age and that this diminished meal-induced thermogenesis may contribute to lower nutrient requirements in old age.