Protein Requirements during Aging

Abstract

Protein recommendations for elderly, both men and women, are based on nitrogen balance studies. They are set at 0.66 and 0.8 g/kg/day as the estimated average requirement (EAR) and recommended dietary allowance (RDA), respectively, similar to young adults. This recommendation is based on single linear regression of available nitrogen balance data obtained at test protein intakes close to or below zero balance. Using the indicator amino acid oxidation (IAAO) method, we estimated the protein requirement in young adults and in both elderly men and women to be 0.9 and 1.2 g/kg/day as the EAR and RDA, respectively. This suggests that there is no difference in requirement on a gender basis or on a per kg body weight basis between younger and older adults. The requirement estimates however are ~40% higher than the current protein recommendations on a body weight basis. They are also 40% higher than our estimates in young men when calculated on the basis of fat free mass. Thus, current recommendations may need to be re-assessed. Potential rationale for this difference includes a decreased sensitivity to dietary amino acids and increased insulin resistance in the elderly compared with younger individuals.

Keywords: elderly; indicator amino acid oxidation; protein; requirements.

Figure 1

A hypothetical pattern of response in nitrogen balance observed due to increasing intakes of protein. A hypothetical example of the relationship between various protein intake levels and the nitrogen balances (true and apparent, 10% overestimated). Application of linear regression analysis on both true and overestimated nitrogen balance values resulted in nitrogen requirements of 100 and 120 mg/kg/day, respectively (0.63 and 0.75 g/kg/day, protein respectively). Application of the two-phase linear regression analysis on both true and overestimated nitrogen balance values resulted in a nitrogen requirement of 120 g/kg/day. Application of linear regression analysis underestimated nitrogen requirements by 20% when the nitrogen balance values were overestimated by 10%. Adapted with permission from [19].

Figure 2

Protein requirements in healthy elderly determined using the IAAO method (a) Women >65 years, n = 12, each subject participated in a minimum of two test intakes for a total of 82 studies, mean (population safe intakes) = 0.96 (1.29) g/kg/day; (b) Men >65 years, n = 6, each subject participated in seven test intakes for a total of 42 studies, mean (population safe intakes = 0.94 (1.24) g/kg/day.

Figure 2

Protein requirements in healthy elderly determined using the IAAO method (a) Women >65 years, n = 12, each subject participated in a minimum of two test intakes for a total of 82 studies, mean (population safe intakes) = 0.96 (1.29) g/kg/day; (b) Men >65 years, n = 6, each subject participated in seven test intakes for a total of 42 studies, mean (population safe intakes = 0.94 (1.24) g/kg/day.