Summary of energy requirements in older individuals and recommendations for future research

The successful validation of the doubly labeled water technique (Schoeller, 1988; Roberts, 1989) has provided an improved means for determining TEE and hence energy requirements in different population groups. Currently available data from 74 subjects (mean ages 64-74 years) studied by four research groups indicate

that the energy requirements of older individuals may be higher than indicated in the current recommended energy requirements (FAO/WHO/UNU, 1985), with mean PAL values for both men and women being 1.641.68. This observation should not be taken as a recommendation for increasing energy intake, but rather as an acceptance of the fact that both energy intake and energy expenditure may be higher than anticipated previously in this age group. Data from our own laboratory also indicate that aTEE/pREE ratios for older adults are lower than those for young men and women by approximately 0.2 PAL on average. Based on reported information on physical activity, it appears likely that these high values for TEE/REE reflect a previous underestimation of energy requirements by the factorial approach rather than unusually high levels of physical activity in the subjects studied. It is important to note that these observations are based on studies in a very limited number of older subjects and many more doubly labeled water measurements are required to provide the information needed for a detailed assessment of changes in energy requirements with age. Future studies are needed to address the following issues:

1. Concerning the methodology of determining energy requirements, more detailed calculations of changes in REE with age after 50 years are required in order to normalize measurements of TEE, considering indices of height as well as weight. It is important to use predicted rather than :measured values for REE when determining TEE/REE ratios because otherwise the TEE/PEE ratio can be substantially influenced by between-laboratory differences in measurement of REE as indicated in Tables 3 and 4. In addition, further standardization of doubly labeled water calculation procedures and more detailed between-laboratory standardization of the doubly labeled water method is needed.
2. Individuals over the age of 50 years are not a homogeneous group with regard to energy requirements. Currently available data are restricted to a relatively narrow age range within the younger section of the older population (mean ages 64-74 years), and much more information is required on changes of TEE with age in individuals in each age decade within the range 50-90 years. Both men and women should be investigated in these studies, as well as young control subjects, so that the range of changes in energy requirements with age can be assessed accurately.
3. There is currently no general consensus over the desirable range of physical activity, and hence energy requirements, for long-term health in older individuals. However, it is clear that a sedentary lifestyle is associated with numerous adverse health consequences and should not be recommended. Although further information on desirable levels of physical activity will necessarily come from investigations with much larger numbers of subjects than are feasible for doubly labeled water measurements, additional studies are needed to define the relationship between TEE and simple measures of physical activity that can be used in larger population studies to predict the energy requirements of representative populations.