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This Article Full Text Full Text (PDF) All Versions of this Article: 295/4/E921    most recent 90536.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Walrand, S. Articles by Nair, K. S. PubMed PubMed Citation Articles by Walrand, S. Articles by Nair, K. S.

Functional impact of high protein intake on healthy elderly people

¹Endocrinology Research Unit, Mayo Clinic School of Medicine, Rochester, Minnesota; and ²Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina

Submitted 24 June 2008 ; accepted in final form 11 August 2008

Decline in muscle mass, protein synthesis, and mitochondrial function occurs with age, and amino acids are reported to enhance both muscle protein synthesis and mitochondrial function. It is unclear whether increasing dietary protein intake corrects postabsorptive muscle changes in aging. We determined whether a 10-day diet of high [HP; 3.0 g protein·kg fat-free mass (FFM)^–1·day^–1] vs. usual protein intake (UP; 1.5 g protein·kg FFM^–1·day^–1) favorably affects mitochondrial function, protein metabolism, and nitrogen balance or adversely affects insulin sensitivity and glomerular filtration rate (GFR) in 10 healthy younger (24 ± 1 yr) and 9 older (70 ± 2 yr) participants in a randomized crossover study. Net daily nitrogen balance increased equally in young and older participants, but postabsorptive catabolic state also increased, as indicated by higher whole body protein turnover and leucine oxidation with no change in protein synthesis. Maximal muscle mitochondrial ATP production rate was lower in older people, with no change occurring in diet. GFR was lower in older people, and response to HP was significantly different between the two groups, with a significant increase occurring only in younger people, thus widening the differences in GFR between the young and older participants. In conclusion, a short-term high-protein diet increased net daily nitrogen balance but increased the postabsorptive use of protein as a fuel. HP did not enhance protein synthesis or muscle mitochondrial function in either young or older participants. Additionally, widening differences in GFR between young and older patients is a potential cause of concern in using HP diet in older people.

dietary protein; protein metabolism; mitochondrial function; kidney function; aging