title: Is protein intake associated with bone mineral density in young women?
abstract: BACKGROUND
  The range of protein intakes for optimizing bone health among premenopausal women is unclear. Protein is a major constituent of bone, but acidic amino acids may promote bone resorption.
  
  
  OBJECTIVE
  The objective was to examine cross-sectional and longitudinal associations between baseline dietary protein and bone mineral density (BMD) among 560 females aged 14-40 y at baseline enrolled in a Pacific Northwest managed-care organization. The role of protein source (animal or vegetable) and participant characteristics were considered.
  
  
  METHODS
  Dietary protein intake was assessed by using a semiquantitative food-frequency questionnaire in participants enrolled in a study investigating associations between hormonal contraceptive use and bone health. Annual changes in hip, spine, and whole-body BMD were measured by using dual-energy X-ray absorptiometry. Cross-sectional and longitudinal associations between baseline protein intake (% of energy) and BMD were examined by using linear regression analysis and generalized estimating equations adjusted for confounders.
  
  
  RESULTS
  The mean (+/-SD) protein intake at baseline was 15.5 +/- 3.2%. After multivariable adjustment, the mean BMD was similar across each tertile of protein intake. In cross-sectional analyses, low vegetable protein intake was associated with a lower BMD (P = 0.03 for hip, P = 0.10 for spine, and P = 0.04 for whole body). For every percentage increase in the percentage of energy from protein, no significant longitudinal changes in BMD were observed at any anatomic site over the follow-up period.
  
  
  CONCLUSIONS
  Data from this longitudinal study suggest that a higher protein intake does not have an adverse effect on bone in premenopausal women. Cross-sectional analyses suggest that low vegetable protein intake is associated with lower BMD.
authors.affiliation: Group Health Research Institute, 1730 Minor Avenue, Suite 1600, Seattle, WA 98101, USA. beasley.j@ghc.org
authors.forename: Jeannette M
authors.initials: JM
authors.lastname: Beasley
authors.forename: Laura E
authors.initials: LE
authors.lastname: Ichikawa
authors.forename: Brett A
authors.initials: BA
authors.lastname: Ange
authors.forename: Leslie
authors.initials: L
authors.lastname: Spangler
authors.forename: Andrea Z
authors.initials: AZ
authors.lastname: LaCroix
authors.forename: Susan M
authors.initials: SM
authors.lastname: Ott
authors.forename: Delia
authors.initials: D
authors.lastname: Scholes
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D000328:Adult; D000818:Animals; D015992:Body Mass Index; D015519:Bone Density / Q000187:drug effects / Q000502:physiology*; D003430:Cross-Sectional Studies; D004032:Diet; D004044:Dietary Proteins / Q000494:pharmacology*; D002149:Energy Intake; D005006:Ethnicity; D015444:Exercise; D005247:Feeding Behavior; D005260:Female; D050723:Fractures, Bone / Q000453:epidemiology; D006801:Humans; D008460:Meat; D044469:Racial Groups; D012907:Smoking / Q000453:epidemiology; D011795:Surveys and Questionnaires; D055815:Young Adult
chemical_list: D004044:Dietary Proteins