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J Nutr. 2015 Jan;145(1):18-24. doi: 10.3945/jn.114.197517. Epub 2014 Oct 15.

Dietary protein requirement of female adults >65 years determined by the indicator amino acid oxidation technique is higher than current recommendations.

Author information

1
Research Institute, Hospital for Sick Children, Toronto, Canada.
2
Department of Pediatrics, School of Population and Public Health, University of British Columbia, Vancouver, Canada Child & Family Research Institute, BC Children's Hospital, Vancouver, Canada.
3
Department of Nutrition Science, Purdue University, West Lafayette, IN.
4
Departments of Nutritional Sciences and Department of Agriculture, Food, and Nutritional Science, University of Alberta, Edmonton, Canada.
5
Research Institute, Hospital for Sick Children, Toronto, Canada Departments of Nutritional Sciences and Pediatrics, University of Toronto, Toronto, Canada; and Department of Agriculture, Food, and Nutritional Science, University of Alberta, Edmonton, Canada.
6
Research Institute, Hospital for Sick Children, Toronto, Canada glenda.courtney-martin@sickkids.ca.

Abstract

BACKGROUND:

Studies on protein requirements in vulnerable groups such as older adults are few, and results are conflicting.

OBJECTIVE:

The main objective of this study was to determine the protein requirements of free-living women >65 y by measuring the oxidation of l-[1-(13)C]phenylalanine to (13)CO2 in response to graded intakes of protein.

METHODS:

Twelve subjects participated in the study, with protein intakes ranging from 0.2 to 2.0 g · kg(-1) · d(-1) for a total of 82 studies. The diets provided energy at 1.5 times each subject's resting energy expenditure and were isocaloric. Protein was given as an amino acid mixture on the basis of the egg protein pattern, except for phenylalanine and tyrosine, which were maintained constant across the protein intake amounts. All subjects were adapted for 2 d before the study day to a protein intake of 1.0 g · kg(-1) · d(-1). The mean protein requirement was determined by applying a mixed-effects change-point regression analysis to F(13)CO2 (label tracer oxidation in (13)CO2 breath), which identified a breakpoint in the F(13)CO2 in response to graded amounts of protein.

RESULTS:

The mean estimated average requirement (EAR) and upper 95% CI (approximating the RDA) protein requirement of women >65 y were 0.96 and 1.29 g · kg(-1) · d(-1), respectively.

CONCLUSION:

These estimates of protein requirements for older women are higher than the current EAR and RDA based on nitrogen balance data, which are 0.66 and 0.80 g · kg(-1) · d(-1), respectively. This trial was registered at clinicaltrials.gov as NCT01604980.

KEYWORDS:

indicator amino acid oxidation; older female adults; phenylalanine oxidation; protein requirement; stable isotope

PMID:
25320185
DOI:
10.3945/jn.114.197517
[Indexed for MEDLINE]

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