Effects of age on energy expenditure and substrate oxidation during experimental underfeeding in healthy men.

Relatively little is known about the influence of age on energy regulation during energy imbalance. We compared the effects of underfeeding on changes in energy expenditure, substrate oxidation, and body energy loss between young men (age 22.0 +/- 0.9 [SEM] years) and older men (age 66.0 +/- 1.8) who were leading unrestricted lives. Changes in total energy expenditure (TEE), resting energy expenditure (REE), the thermic effect of feeding (TEF), respiratory quotient, and body energy loss were determined in response to undereating by 3.17 +/- 0.16 Megajoule (MJ)/day for 21 days in 19 healthy subjects consuming a typical diet. No significant effects of age were observed in changes in TEE, REE, TEF, or body energy loss in response to underfeeding. Thus, older men do not appear to have any impairment of energy conservation during negative energy balance compared to young men. This normal pattern of energy conservation during undereating together with the previously demonstrated reduction in energy dissipation during overeating can be predicted to promote body fat deposition in older men during the cycles of positive and negative energy balance that occur during normal life. This finding may help to explain the increased body fat mass in older individuals.