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Total energy expenditure of older individuals

To our knowledge, there are six studies of TEE in older individuals that have been published (Prentice et al, 1988; Goran & Poehlman, 1992; Roberts et al, 1992; Reilly et al, 1993; Sawaya et al, 1994; Pannemans & Westerterp, 1995). In these studies, a total of 38 free living men, 36 free-living women and 14 hospitalized male and female mental patients have been investigated (Table 2), and these within the younger segment of older individuals. In only three of the six studies (31 men and 20 women) were there measurements in young as well as in older subjects.

Table 3 gives a summary of relevant details of the subjects and data from the studies in older men (mean ages 64-74 years). The values for TEE are those reported by the authors, as well as 'adjusted' mean values (aTEE) which represent our effort to standardize calculation procedures between groups. As described in the legend to the table, the adjusted values all include a 2% increase in TEE to account for the expected lower rate of fractionated water loss in older individuals (Roberts et al, 1992). In addition, data of Goran & Poehlman (1992) were adjusted to take into account the fact that they used a mean measured ratio of the dilution spaces (²H₂O: H₂ ¹⁸O) which was higher than the values used in the other studies. Although the necessity of using group-specific dilution space ratios has been considered, there is currently no available evidence to support the validity of this approach and, as noted by Goran & Poehlman (1992), it results in calculated values for TEE 10.5% lower than the use of a standard mean dilution space ratio of 1.03 (Schoeller et al, 1986).

Table 3 Published values for total energy expenditure in free-living older men measured using the doubly labeled water method^a

^a Values are group means with ± s.d.. where data are available.
^b Predicted values for REE determined from body weight using FAO/WHO/UNU (1985) equations.
^c Adjusted values:
^d for Goran & Poehlman (1992) are increased by 12.71% (10.5% for possible underestimation of TEE associated with using high ratio for the
²H: ¹⁸O dilution space, and 2% for lower rate of insensible water loss in elderly subjects as predicted by Roberts et al (1992));
^e for Pannemans & Westerterp (1995) increased by 2% for lower rate of insensible water loss in elderly subjects as predicted by Roberts et al (1992). Note that the observed negative energy balance in this population is not accounted for in the adjusted TEE.

The reported and adjusted values for TEE in older men are given in Table 3, expressed as absolute values as well as ratios of mREE and pREE (FAO/WHO/ UNU, 1985). It can be seen that both the adjustment to TEE, as well as whether mREE or pREE is the chosen denominator, exert a significant influence on the PAL index in some individual studies. The ratio aTEE/pREE may represent the best estimate of energy requirements in this group. It should be noted that the aTEE/pREE ratio for the study of Goran & Poehlman (1992) differs significantly from data of the other two studies. Excluding the data of Goran & Poehlman (1992), a mean aTEE/pREE of 1.66 is obtained. This value is very slightly higher than the current recommended value of 1.51 for older individuals.

Data on the TEE of older women are given in Table 4. As with the studies in men, there is a relatively narrow range for mean age in these studies, ranging from 64 to 74 years. The reported and adjusted values for TEE are given in the table, expressed as absolute values as well as ratios of the mREE and pREE (FAO/ WHO/UNU, 1985). As seen in the data from men, both the adjustment to TEE and the use of mREE compared to pREE, exert a significant influence on the TEE/PEE ratio in some individual studies (Table 4). The mean aTEE/pREE ratio for all studies combined is 1.71, and in this case data from the study of Goran & Poehlman (1992) do not appear to lie outside the range of the other studies. The mean unadjusted TEE/pREE (1.64) is somewhat lower than the aTEE/pREE, but as with the data from men this value is higher than the current recommended value of 1.51 (FAO/WHO/UNU, 1985).

A combined summary of data from men and women is given in Table 5. Taken together, the studies on men and women provide no evidence of any influence of gender on TEE/pREE in older individuals, although it should be noted that the mean TEE/PEE ratio is indeed lower in women than in men in our own studies, which to our knowledge have involved the largest number of older subjects studied by any one group (Roberts et al, 1992; Sawaya et al, 1995). After excluding data that are influenced by the use of different doubly labeled water calculation procedures and the use of measured vs predicted values for REE, the weighted mean aTEE/pREE ratio for men and women combined is 1.66 and the mean TEE/pREE ratio is 1.64. Both of these values are higher than the current suggested value (1.51 for persons >50 years). It might be hypothesized that these values could be high because of a positive adaptation in energy expenditure to overeating during the TEE measurements. However, our recent overfeeding studies in young and older men have indicated that there is only a small increase in TEE with short term overfeeding (averaging 165 kcal/d) and this is due primarily to an increase in REE associated with increased fat and fat-free mass (Roberts et al, 1990). Thus, the ratio of TEE/PEE does not increase with overeating, and it would appear that adaptive variations in TEE due to overeating should not be of significant concern when using measurements of TEE to examine energy requirements.

Another important question concerning the energy requirements of older individuals is how TEE/PEE changes with age. Although there is little information on this issue, current recommended dietary allowances assume a modest decrease in TEE/pREE up to the age of 50 years (FAO/WHO/UNU, 1985). Our own studies in both young and older men and women (Roberts et al, 1992; Sawaya et al, 1995) support the suggestion of a modest decrease in TEE/pREE between the ages of 25 and 70 years. To quantify this change further, we performed a multiple regression analysis on our combined data set of 55 young and older men and women. The most significant predictor of TEE/pREE was percent body fat (since fat free mass is already accounted for through its close association with REE) and neither gender nor age was significant when included in models with percent fat (data not shown). Thus, the PAL index can be expected to fall with age in association with the usual increase in the proportion of body fat content.

Table 4 Published values for total energy expenditure in free-living older women measured using the doubly labeled water method^a

^a Values are group means with ± s.d. where data are available.
^b Predicted values for REE determined from body weight using FAO/WHO/UNU (1985) equations.
^c Adjusted values:
^d for Goran &: Poehlman (1992) are increased by 12.71% (10.5% for possible underestimation of TEE associated with using high ratio for the ²H: ¹⁸O dilution space, and 2% for lower rate of insensible water loss in elderly subjects as predicted by Roberts et al (1992));
^e for Reilly et al 1993) increased by 2% for lower rate of insensible water loss in elderly subjects as predicted by Roberts et al (1992);
^f for Pannemans & Westerterp (1995) increased by 2% for lower rate of insensible water loss in elderly subjects as predicted by Roberts et al (1992). Note that the observed negative energy balance in this population is not accounted for in the adjusted TEE.

Table 5 Summary of weighted means for PAL indicators in older men and women

^a Excluding data of Goran & Poehlman (1992), which are strongly influenced by the use of data for adjusted TEE and pREE.

Relationship between total energy expenditure and physical activity

The measurements of TEE described above indicate that the measured TEE/pREE of the groups of subjects studied (mean ages 64-74 years) was higher than the current recommended value for the age group > 50 years. This may indicate that current recommendations for energy (FAO/WHO/UNU, 1985) underestimate the usual energy need of older adults. However, it is alternatively possible that the physical activity of the subjects in those studies was unusually high. The lack of standardization in reporting of physical activity hampers an assessment of this issue. Concerning the studies conducted in our own laboratory, the mean values for self-reported durations of strenuous activity were 29 and 48 min/day for men and women, respectively (Roberts et al, 1992; Sawaya et al, 1995). These values included means of 4 and 7 min/day, respectively, for activities with predicted energy expenditure of >5 × REE. Thus, these groups of subjects did not appear to be unusually active, indicating that the 1985 recommendations on energy requirements may indeed be lower than usual energy needs. However, further research is needed to confirm this suggestion. In the study of Reilly et al (1993), a mean duration of leisure time activity of 40 min/day was reported together with 87 min/day of walking. These mean activity data appear relatively high, in keeping with the high mean PAL index in this group (aTEE/pREE = 1.84).

Another factor to consider in the determination of recommended energy requirements for older individuals is the issue of normal vs desirable levels of physical activity. Physical activity is the major determinant of variability in TEE/PEE between individuals and can potentially have a major effect on energy requirements. Figure 1 illustrates the relationship between strenuous physical activity (defined as the sub-set of self-reported strenuous activity with an expected mean energy cost of >5 × REE) and TEE/pREE (equal to aTEE/pREE) in our population of older men. It can be seen that, as expected, high levels of reported strenuous activity were associated with increased TEE/pREE. Individuals who reported no strenuous physical activity had a mean value for TEE/pREE of 1.70 while those who reported 30 min/day of strenuous physical activity had a mean TEE/PEE ratio of 1.90. Although it is widely accepted that a sedentary existence is associated with increased morbidity and mortality (Paffenbarger et al, 1986; Blair et al, 1989; Helmrich et al, 1991; Paffenbarger et al, 1993), there is no general consensus over what levels and types of physical activity are optimal for long-term health (Paffenbarger et al, 1986; Blair et al, 1989; Helmrich et al, 1991; Paffenbarger et al, 1993). For this reason, it is appropriate to continue to make recommendations for different levels of physical activity, and also to recommend a minimum activity level that makes allowance for some strenuous physical activity for cardiovascular maintenance.

Effects of energy balance on nitrogen balance

Reliable measurement and knowledge of energy requirements of the elderly is essential to the accurate determination of protein requirements. Negative energy balance results in negative N balance (because lean tissue is mobilized along with fat and glycogen), and positive energy balance promotes positive N balance. A summary of data from several N balance studies by Pellett & Young (1992) indicated that even very small discrepancies in energy balance can have a major impact on the outcome of N balance: an energy imbalance of only 1 kcal/kg changes N balance by 1 mg/kg. It is not possible to measure the energy balance of individual subjects to 65 kcal/d in short-term studies ( < 30 days), which means that data on N balance from individual subjects should not be used to judge the adequacy of protein intake. Such data can only be used as the average of groups in which small variations in energy intake above and below actual energy expenditure can be expected to cancel out. Because energy requirements may have been underestimated in many previous studies, there is a potential bias towards overestimation of protein requirements in N balance experiments in older subjects.

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