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Protein requirements of elderly people

Introduction: current dietary protein requirement recommendations
Protein requirement studies in elderly people: previously reviewed data
Protein requirement studies in elderly people: reassessment of previously reviewed data
Summary
References
Discussion
References

WW Campbell and WJ Evans

Noll Physiological Research Center, The Pennsylvania State University, University Park, PA 16802, USA

Descriptors: protein, nitrogen balance, ageing

Introduction: current dietary protein requirement recommendations

the current mean dietary protein requirement for healthy adult men and women of all ages, as set by the 1985 joint fao/who/unu expert consultation, is estimated to be 0.6 g protein/kg/d, with a suggested safe level of intake set at 0.75 g protein/kg/d. these protein requirements and allowance estimates were established using a standard method of nitrogen (n) balance in young men, and making extrapolations for older adults and the elderly. while acknowledging that various changes (including progressive changes in body composition, physiological functional capacity, physical activity, total food intake, and frequency of disease) occur with advancing chronological age, all of which might be expected to contribute to altered protein requirements, the consultation felt that insufficient data were available from studies conducted with elderly subjects to determine protein requirements with confidence. it noted that the suggested safe level of protein intake should not be lower than the recommendations for younger adults and suggested that the elderly may utilize dietary protein less efficiently..

Correspondence to: William J. Evans, Noll Physiological Research Center, 119 Noll Laboratory, The Pennsylvania State University, University Park, PA 16802, USA.

Protein requirement studies in elderly people: previously reviewed data

Protein requirement studies in elderly subjects, utilizing the N balance technique as the standard method of assessment, have been conducted by several research groups during the past 16 years (Table 1). Data that were available to and reviewed by the 1985 Consultation included the studies by Cheng et al, Uany et al, Zanni et al and Gersovitz et al. These studies did indeed provide conflicting results, with some studies (Cheng et al, 1978; Zanni et al, 1979) concluding that 0.75 g protein/kg/d is adequate, and others (Gersovitz et al, 1982; Uany et al, 1978) concluding that this protein intake is inadequate for N equilibrium in elderly individuals. Differences in results and conclusions among these four studies may be due, in part, to differences in physiologic and metabolic status of subjects within each study and between the studies, as well as differences in study design and the assumptions used in calculating N balance. Indeed, each study used a somewhat different formula to calculate N balance, none of which was exactly the formula recommended for use by the 1985 Consultation.

Cheng et al (1978) estimated that a mean protein intake of 0.77 g protein/kg/d was required for N equilibrium in seven elderly male nursing home residents. They concluded that 0.8 g protein/kg/d high-biological-value protein was adequate for these elderly men.

Table 1 Protein requirement studies in elderly people: subjects and protein intake information

M = male, F = female.

However, each subject's N balance was overestimated by not accounting for miscellaneous N losses, and no upward adjustment was made in the mean protein requirement to provide a safe level of protein intake for nearly all elderly people.

Uauy et al (1978) measured N balance in seven elderly women and seven elderly men provided weight maintenance diets for 10-day periods with various quantities of whole-egg as the protein source. Mean N equilibrium was calculated to be 0.83 g protein/kg/d in the elderly women, and estimated to range from 0.7 to 0.85 g protein/kg/d in elderly men. The authors concluded that these elderly women and men would obtain adequate protein with diets providing 12-14% of total energy intake as protein. This roughly corresponded to protein intakes of 0.95-1.10 g protein/kg/d for these elderly women and 0.830.97 g protein/kg/d for these elderly men, based on calculated mean energy intake data provided in the original publication. Uany et al did not specifically adjust the mean protein requirement upward to provide most elderly people with a safe level of protein intake.

Zanni et al (1979) estimated a mean protein requirement of 0.46 g protein/kg/d based on data from six elderly men, and concluded that the 1973 FAO/WHO safe intake of 0.57 g protein/kg/d was adequate for apparently healthy elderly men. Nitrogen balance was determined while each man consumed either a protein free diet for 17 days, or diets providing either about 1.44 or 1.73 times measured endogenous N losses (15 days each period). Several factors may have contributed to an underestimation of actual protein requirements in this study, including the measurement of differences in N balance over a small range of inadequate protein intakes (0.36-0.46 g protein/kg/d), including data from the protein-free balance period in the N balance calculations when it is generally recognized that this will lower the protein requirement estimate due to non-linearity of the N balance response in this submaintenance range (FAO/WHO/UNU, 1985), and increasing N retention by not providing a restabilization period between the 17-day protein-free balance period and the other balance periods.

Gersovitz et al (1982) provided weight-maintaining diets with ().8 g protein/kg/d to seven elderly men and eight elderly women continuously for 30 days. Nitrogen balance was assessed on study days 6-10, 16-20 and 26-30. During the initial 10-day period, all seven men and four of eight women were in negative balance. Mean N balance was improved (i.e. N equilibrium reached) for both men and women on days 26-30, but three men (43%) and four women (50%) were in negative N balance. These long-term N balance data indicated that 0.8 g protein/kg/d was not adequate for a majority of elderly men and women.

Table 2 Protein requirement assessments in elderly people

M = male, F == female.
^a Recalculated data presented by Campbell et al (1994).
^b Lower and upper limits of 95% confidence interval.
^c 1985 FAO/WHO/UNU nitrogen balance formula used for original calculation of protein requirement.

Protein requirement studies in elderly people: reassessment of previously reviewed data

When comparing results and conclusions of these studies (Cheng et al, 1978, Gersovitz et al, 1982; Uauy et al, 1978; Zanni et al, 1979), it would be helpful if the same N balance formula was used and the same assumptions were applied to the calculations. To this end, Campbell et al (1994), recently reassessed the N balance data from each of these studies using the N balance formula recommended by the 1985 Consultation. This reassessment was possible because individual subjects' N balance data had been published in each of the original articles. The results are shown in Table 2. Recalculation of the data from Cheng et al (1978) increased the mean protein requirement by 21%, to 0.93 ± 0.05 g protein/kg/d, with the increase mainly due to the inclusion of a factor for miscellaneous N losses in the balance formula. Data from the elderly women and men studied by Uauy et al (1978) were combined and a mean protein requirement of 0.81 ± 0.09 g protein/kg/d calculated. The similarity of this value to the original protein requirement estimates by Uauy et al was expected, since an increase in the estimated miscellaneous N losses from 5 mg to 8 mg N/kg/d was the only change in the N balance formula used. Upon recalculation of the data of Zanni et al (1979), the mean protein intake required for N equilibrium increased by 41%, to 0.65 ± 0.19 g protein/kg/d. This dramatic increase was due mainly to the exclusion of data collected during the 17-day protein-free period from the regression. When the recalculated data from all three studies were combined by weighted mean averaging, a mean protein requirement of 0.89 ± 0.05 g protein/kg/d was estimated (Campbell et al, 1994).

Protein requirement studies in elderly people: new data

In addition to the retrospective reassessment of data from these N balance studies of elderly subjects (Cheng et al, 1978; Uauy et al, 1978; Zanni et al, 1979), Campbell et al (1994) also provided N balance data on 12 men and women, aged 56-80 years, who consumed weight-maintenance diets providing either 0.8 or 1.6 g protein/kg/d. A mean protein requirement for N equilibrium of 1.0 g protein/kg/d was estimated based on N balance data collected during days 6-11 of this short term N balance study. This study was limited by the assessment of N balance at only two levels of protein intake, and the lack of opportunity to calculate separate protein requirements for each subject, because each subject consumed only one of the experimental diets. However, it is noteworthy that the lower limit of the 95% confidence interval for the 1.0 g protein/kg/d mean protein requirement is 0.72 g protein/kg/d, a value considerably greater than the 0.6 g protein/kg/d mean protein requirement established by the 1985 Consultation for adults of all ages.

The 1.0 g protein/kg/d mean protein requirement estimated by Campbell et al (1994) is similar to the 0.97 g protein/kg/d mean protein intake that maintained 24 healthy men and women, aged 70-86 years, in N equilibrium (Bunker et al, 1987). Homebound elderly people, aged 7086 years, were reported to be in marked negative N balance at a mean protein intake of 0.67 g protein/kg/d. These data by Bunker et al (1987) actually overestimate N balance because no factor for miscellaneous N losses was used in the balance calculation.

A summary of the new data from Campbell et al (1994), and the recalculation of data from Cheng et al (1978), Uauy et al (1978) and Zanni et al (1979), is provided in Figure 1. A weighted mean protein requirement for elderly people of 0.91 ± 0.043 g protein/kg/d was estimated from data of these four studies combined. As shown, the estimated mean protein requirement in three of the four studies is higher than the safe level of 0.75 g protein/kg/d recommended by the 1985 Consultation for adults of all ages.

After a mean protein requirement is established, an upward adjustment should be made to establish a safe level of intake (recommended allowance) to meet the metabolic needs of virtually all adults. The Consultation (1985) estimated the coefficient of variation of protein requirements of young adults at 12.5%, and suggested that the dietary protein needs of 97.5% of individuals in this population group would be met with a protein intake 25% above the mean protein requirement. Based on this estimate, a safe protein intake for elderly men and women would be 1.0 g protein/kg/d or more high quality protein.

Table 3 Conclusions from protein requirement studies in elderly people

The 1985 report acknowledged that no longer-term N balance data in elderly subjects were available when the Consultation met in October 1981, other than the 30-day balance data of Gersovitz et al (1982). Recently Castenada et al (1995) completed a study assessing longer-term (9 weeks) adaptation to marginal protein intakes in 12 elderly women aged 66-79 years. Subjects consumed weight-maintenance diets providing either 0.45 or 0.92 g protein/kg/d, and N balance was measured for 6-day periods during study weeks 3 and 9. All six women provided 0.45 g protein/kg/d were in negative N balance during week 3 (group mean -15.3 ± 3.3 mg N/kg/d), and the mean negative N balance moved significantly toward N equilibrium at week 9 (group mean - 5.2 ± 1.3 mg N/kg/d). However, this shift in N balance occurred only after these elderly women had accommodated with an 8% decline in body cell mass (assessed by potassium-40 scanning) and an 8% decline in muscle mass (assessed by urinary creatinine). Five of these six women remained in negative balance at week 9. The six women provided 0.92 g protein/kg/d achieved N equilibrium throughout the study, with a mean balance of 7.5 ± 6.3 and 1.7 ± 2.5 mg N/kg/d at weeks 3 and 9, respectively, and maintained body cell mass and muscle mass.

At week 3, a mean protein requirement of 0.78 g protein/kg/d for N equilibrium may be estimated from regression analysis of data from both the 0.45 and 0.92 g protein/kg/d groups. A similar estimated mean protein requirement may be calculated at week 9 (0.82 g protein/ kg/d). Thus, both short- and longer-term N balances support previous reports (Campbell et al, 1994; Gersovitz et al, 1982; Uauy et al, 1978) demonstrating higher protein requirements in healthy elderly subjects.

Short-term N balance studies (1-3 week study periods) have criticized for allowing inadequate time to fully adapt to steady-state at a given protein intake level. Indeed, these data (Castaneda, 1995), and those of Gersowitz et al (1982), show that N balance tends to move toward equilibrium (i.e. zero balance) when extended past 3 weeks in elderly men and women. That the mean protein requirement estimates in elderly women were similar at both 3 and 9 weeks, despite this shift, however, supports the conclusion that short-term balance studies are predictive of protein requirements that would be estimated from longer-term studies (Campbell, 1994). This is fully consistent with the close similarity of mean protein requirement estimates from short- and longer-term balance studies, 0.63 and 0.58 g protein/kg/d, respectively in studies reviewed by the 1985 Consultation in young men. In addition, the data of Castaneda et al demonstrate that N equilibrium shown in longer-term balance studies may be established as a result of significant detrimental changes in body composition. Thus, N balance data generated from longer-term studies do not provide an accurate assessment for protein requirements of subjects in the metabolic state in which they entered the study.

Thus available assessments of protein requirements utilizing both short- and longer-term N balance techniques suggest that the mean protein requirement of elderly men and women may be ³ 0.8 g protein/kg/d. This would indicate a safe level of intake for most elderly people of ³ 1.0 g protein/kg/d.

Summary

Based on N balance calculated in accord with the recommendations of the 1985 Joint FAO/WHO/UNU Expert Consultation, a summary of conclusions from the six N balance studies in elderly people is presented in Table 3. The data, with one flawed exception, indicate that the safe level of protein intake for older adults may be higher than currently recommended.

In the only study directly comparing elderly and young subjects (Cheng et al, 1978), no differences in protein requirement were found. However, the data suggest that the 0.8 g protein/kg/d would be inadequate for both groups. Additional direct comparisons between younger and older adults are desirable as a basis for any revised recommendations.

In the only study directly comparing the protein requirements of both elderly men and women (Uauy et al, 1978), the variability was too great to allow adequate assessment of possible gender differences. More research is needed to determine whether gender-related differences occur.

References

Bunker VW, Lawson MS, Stanfield MF & Clayton BE (1987): Nitrogen balance studies in apparently healthy elderly people and those who are housebound. Br. J. Nutr. 47, 211-221.

Campbell WW, Crim MC, Dallal GE, Young VR & Evans WJ (1994): Increased protein requirements in elderly people: new data and retrospective reassessments. Am. J. Clin. Nutr. 60, 501-509.

Castaneda C, Charnley JM, Evans WJ & Crim MC (1995): Elderly women accommodate to a low-protein diet with losses of body cell mass, muscle function, and immune response. Am. J. Clin. Nutr. 62, 30-39.

Cheng A, Gomez A, Bergan, J. Tung-Ching L, Monckeberg F & Chichester C (1978): Comparative nitrogen balance study between young and aged adults using three levels of protein intake from a combination wheat-soy-milk mixture. Am. J. Clin. Nutr. 31, 12-22.

FA/WHO/UNU (1985): Energy and protein requirements. Technical Report Series 724. Geneva: World Health Organization.

Gersovitz M, Munro H. Scrimshaw N & Young V (1982: Human protein requirements: assessment of the adequacy of the current recommended dietary allowance for dietary protein in elderly men and women. Am. J. Clin. Nutr. 35, 6 14.

Uauy R. Scrimshaw N & Young V (1978): Human protein requirements: nitrogen balance response to graded levels of egg protein in elderly men and women. Am. J. Clin. Nutr. 31, 779-785.

Zanni E, Calloway D & Zezulka A (1979): Protein requirement of elderly men. J. Nutr. 109, 513-524.

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