Does Aging Affect Diet-Induced Thermogenesis? Revisiting the Evidence from Human Studies.

Abstract

Purpose of review: As life expectancy increases and the proportion of older adults grows worldwide, understanding how aging influences components of energy metabolism has become increasingly relevant. Diet-induced thermogenesis (DIT)-the increase in metabolic rate following food intake-accounts for approximately 10% of total daily energy expenditure. Aging has been proposed to attenuate DIT, potentially contributing to age-related reductions in energy expenditure and other metabolic changes. Here, we review available evidence from human studies on the effect of aging on DIT and explore potential methodological and physiological factors that may explain discrepancies across studies.

Recent findings: Fourteen studies comparing younger and older adults were included. Six reported significantly lower DIT in older individuals, whereas eight found no age-related differences. One of the most consistent patterns identified across studies was the influence of postprandial measurement duration on study outcomes. Studies reporting lower DIT in older adults assessed postprandial energy expenditure over shorter durations (≤ 240 min), while those employing longer measurement protocols found no differences. Variations in body composition, particularly a lower fat-free mass in older adults, were frequently observed but did not consistently explain the reported age effects. Mechanistic factors including sympathetic nervous system activity, gastric emptying, and macronutrient composition of the test meals have been investigated, yet available evidence does not support a consistent role for these factors in mediating age-related differences in DIT. Whether aging independently alters DIT in humans remains uncertain. The findings of this narrative review suggest that methodological factors, particularly the duration of measurement, may influence the detection of age-related differences in DIT. Future studies using adequately powered designs, standardized meal protocols, and matching or adjusting for body composition are required to clarify whether aging per se alters postprandial thermogenesis.