title: Dietary Protein Requirement of Men >65 Years Old Determined by the Indicator Amino Acid Oxidation Technique Is Higher than the Current Estimated Average Requirement.
abstract: BACKGROUND
  The current estimated average requirement (EAR) and RDA for protein of 0.66 and 0.8 g ⋅ kg-1 ⋅ d-1, respectively, for adults, including older men, are based on nitrogen balance data analyzed by monolinear regression. Recent studies in young men and older women that used the indicator amino acid oxidation (IAAO) technique suggest that those values may be too low. This observation is supported by 2-phase linear crossover analysis of the nitrogen balance data.
  
  
  OBJECTIVE
  The main objective of this study was to determine the protein requirement for older men by using the IAAO technique.
  
  
  METHODS
  Six men aged >65 y were studied; each individual was tested 7 times with protein intakes ranging from 0.2 to 2.0 g ⋅ kg-1 ⋅ d-1 in random order for a total of 42 studies. The diets provided energy at 1.5 times the resting energy expenditure and were isocaloric. Protein was consumed hourly for 8 h as an amino acid mixture with the composition of egg protein with L-[1-13C]phenylalanine as the indicator amino acid. The group mean protein requirement was determined by applying a mixed-effects change-point regression analysis to F13CO2 (label tracer oxidation in breath 13CO2), which identified a breakpoint in F13CO2 in response to graded intakes of protein.
  
  
  RESULTS
  The estimated protein requirement and RDA for older men were 0.94 and 1.24 g ⋅ kg-1 ⋅ d-1, respectively, which are not different from values we published using the same method in young men and older women.
  
  
  CONCLUSIONS
  The current intake recommendations for older adults for dietary protein of 0.66 g ⋅ kg-1 ⋅ d-1 for the EAR and 0.8 g ⋅ kg-1 ⋅ d-1 for the RDA appear to be underestimated by ∼30%. Future longer-term studies should be conducted to validate these results. This trial was registered at clinicaltrials.gov as NCT01948492.
authors.affiliation: Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Mahroukh
authors.initials: M
authors.lastname: Rafii
authors.affiliation: Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Karen
authors.initials: K
authors.lastname: Chapman
authors.affiliation: Department of Pediatrics, School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada.|Child and Family Research Institute, British Columbia Children's Hospital, Vancouver, British Columbia, Canada.
authors.forename: Rajavel
authors.initials: R
authors.lastname: Elango
authors.affiliation: Department of Nutrition Science, Purdue University, West Lafayette, IN.
authors.forename: Wayne W
authors.initials: WW
authors.lastname: Campbell
authors.affiliation: Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada.|Department of Pediatrics, University of Toronto, Toronto, Ontario, Canada.|Department of Agriculture, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Ronald O
authors.initials: RO
authors.lastname: Ball
authors.affiliation: Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.|Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada.|Department of Pediatrics, University of Toronto, Toronto, Ontario, Canada.|Department of Agriculture, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Pencharz
authors.affiliation: Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.|Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Glenda
authors.initials: G
authors.lastname: Courtney-Martin
keywords: indicator amino acid oxidation; older men; phenylalanine oxidation; protein requirement; stable isotope