An underfeeding study in healthy men and women provides further evidence of impaired regulation of energy expenditure in old age

The effect of aging on energy regulation remains controversial. We compared the effects of underfeeding on changes in energy expenditure and respirato ry quotient in young normal weight men and women [YNW, age 25.7 +/- 3.2 y(S D), body mass index (BMI) 23.1 +/- 1.6 kg/m(2)], young overweight men and w omen (YOW, age 26.1 +/- 3.5 y, BMI 27.7 +/- 2.1 kg/m(2)) and older (OLD) me n and women (age 68.4 +/- 3.3 y, BMI 27.4 +/- 3.4 kg/m(2)). The thermic eff ect of feeding (TEF) during weight maintenance, and changes in resting ener gy expenditure (REE) and respiratory quotient were determined in response t o undereating by an average 3.75 MJ/d for 6 wk. In addition, body compositi on was measured. No significant differences among the groups were observed in TEF, fasting and postprandial respiratory quotient, or the change in fas ting respiratory quotient with underfeeding. However, REE adjusted for fat- free mass and fat mass was significantly lower in OLD subjects compared wit h YNW and YOW subjects (P < 0.05), In addition, the REE response to weight change was significantly attenuated in the OLD subjects (P = 0.023). These data suggest that the responsiveness of energy expenditure to negative ener gy balance is attenuated in old age, and provide further support for the hy pothesis that mechanisms of energy regulation are broadly disregulated in o ld age.