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Dietary protein and bone health: harmonizing conflicting theories

Authors

  • Matthew P Thorpe,

    Corresponding author
    1. Division of Nutritional Science, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
      MP Thorpe, Division of Nutritional Science, University of Illinois at Urbana-Champaign, 237 Freer Hall, 906 S Goodwin, Urbana, IL 61801, USA. E-mail: mthorp3@illinois.edu, Phone: +1-217-265-8490, Fax: +1-217-244-7322.
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  • Ellen M Evans

    1. Division of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
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  • Significant portions of this manuscript have been included in the doctoral dissertation of MP Thorpe. Dissemination of that dissertation outside of the University of Illinois has been embargoed pending scholarly publication.

MP Thorpe, Division of Nutritional Science, University of Illinois at Urbana-Champaign, 237 Freer Hall, 906 S Goodwin, Urbana, IL 61801, USA. E-mail: mthorp3@illinois.edu, Phone: +1-217-265-8490, Fax: +1-217-244-7322.

Abstract

A precise understanding of the role of dietary protein in bone health has been evasive despite decades of research. It is known that a dietary acid load is harmful to bone, and sulfur-containing amino acids are metabolized to provide such an acid load. It is also known that protein elevates urine calcium loss. However, recent clinical studies and a meta-analysis have indicated either no effect or a modest benefit associated with higher protein intakes. These contradictory considerations may be explained by the existence of a two-faced relationship between protein and bone, with simultaneous positive and negative pathways. In opposition to the negative effects of dietary acid load, protein may exert positive effects related to improving calcium absorption, increasing insulin-like growth factor 1, or improving lean body mass, which, in turn, improves bone strength. Putative mechanisms behind these pathways are reviewed here, and some limitations in the historical literature as well as suggested measures to counter these in the future are identified. When positive and negative pathways are considered in tandem, protein may offer modest benefits to bone in the presence of adequate dietary calcium and acid-neutralizing fruits and vegetables.

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