Dietary energy requirements of young and older women determined by using the doubly labeled water method.

There is little information on the effects of age on energy requirements in women. This issue was investigated in a cross-sectional study of 10 normal-weight young women aged 25.2 +/- 1.1 y (mean +/- SEM) and 10 normal-weight older women aged 74.0 +/- 1.4 y. In a 9-d study, measurements were made of free-living total energy expenditure (TEE) by using the doubly labeled water technique, body composition by using hydrodensitometry, and resting energy expenditure (REE) by using indirect calorimetry. Mean values for reported levels of strenuous activity were within the expected range in both groups (31 +/- 13 min/d in the young group and 7 +/- 2 min/d in the older group). Energy requirements expressed as the ratio of TEE to REE were 1.80 +/- 0.10 and 1.62 +/- 0.06 (P < 0.01) in the young and older group, respectively. When values for REE predicted from body weight (pREE) were used, as suggested in the current recommended dietary allowances (RDAs), the ratios of TEE to pREE in the two groups were 1.85 +/- 0.10 and 1.54 +/- 0.04 (P < 0.05). The RDAs significantly under-predicted the energy requirements of the young group (P < 0.05), but there was no significant underprediction in the older group. Although obtained in a relatively small number of subjects, these results provide no evidence to indicate that the current RDAs underestimate the energy requirements of older women, in contrast with previous observations of an underestimation of energy requirements by the RDAs in older men.