title: Higher Protein Intake Is Associated with Higher Lean Mass and Quadriceps Muscle Strength in Adult Men and Women.
abstract: BACKGROUND
  The impact of dietary protein intake on lower extremity lean mass and strength in community-dwelling adult Americans is not fully understood.
  
  
  OBJECTIVE
  The objective was to determine the associations between total protein (TP), animal protein (AP), and plant protein (PP) intakes and lean mass of the legs and quadriceps muscle strength. We further examined whether the associations with quadriceps strength may be explained by lean mass of the legs.
  
  
  METHODS
  This cross-sectional study included men (n = 1166) and women (n = 1509) from the Framingham Offspring Cohort in Massachusetts. Protein intake in grams per day was measured in either 1995-1998 or 1998-2001. Leg lean mass and isometric quadriceps strength, both in kilograms, were measured in 1996-2001. Multilinear regression models estimated adjusted least squares means of each of the muscle measures by quartile categories of protein intake, adjusting for relevant confounders and covariates.
  
  
  RESULTS
  Mean age was 59 ± 9 y (range: 29-86 y) and TP intake was 80 ± 27 g/d in men and 76 ± 26 g/d in women. In men and women, leg lean mass was higher in participants in the highest quartiles of TP and AP intake compared with those in the lowest quartiles of intake [least squares means (kg): TP-17.6 vs. 17.1 in men, P-trend: 0.005, and 11.7 vs. 11.4 in women, P-trend: 0.006; AP-17.6 vs. 17.1 in men, P-trend: 0.002, and 11.7 vs. 11.4 in women, P-trend: 0.003]. PP intake was not associated with lean mass in either sex. In men and women, quadriceps strength was higher in participants in the highest quartile of PP intake compared with those in the lowest quartile [least squares means (kg): 22.9 vs. 21.7 in men, P-trend: 0.01, and 19.0 vs. 18.2 in women, P-trend: 0.01]; this association was no longer significant after adjustment for fruit and vegetable intake (P-trend: 0.06 in men and 0.10 in women). Although no significant association was observed for AP intake in either sex, nonsignificant protective trends were observed for TP intake (P-trend: 0.08 in men and 0.10 in women).
  
  
  CONCLUSIONS
  Our findings suggest that maintaining adequate protein intake with age may help preserve muscle mass and strength in adult men and women. Dietary protein types may differentially affect muscle mass and strength. Whether PP is a marker of dietary quality or has a direct effect on muscle strength (independent of lean mass) needs to be further clarified.
authors.affiliation: Institute for Aging Research, Hebrew SeniorLife, Department of Medicine, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, MA ShivaniSahni@hsl.harvard.edu.
authors.forename: Shivani
authors.identifier: http://orcid.org/0000-0002-9827-0986
authors.initials: S
authors.lastname: Sahni
authors.affiliation: Institute for Aging Research, Hebrew SeniorLife, Department of Medicine, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, MA.
authors.forename: Kelsey M
authors.initials: KM
authors.lastname: Mangano
authors.affiliation: Institute for Aging Research, Hebrew SeniorLife, Department of Medicine, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, MA.
authors.forename: Marian T
authors.initials: MT
authors.lastname: Hannan
authors.affiliation: Institute for Aging Research, Hebrew SeniorLife, Department of Medicine, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, MA.
authors.forename: Douglas P
authors.initials: DP
authors.lastname: Kiel
authors.affiliation: Institute for Aging Research, Hebrew SeniorLife, Department of Medicine, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, MA.
authors.forename: Robert R
authors.initials: RR
authors.lastname: McLean
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D004044:Dietary Proteins / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D008297:Male; D008404:Massachusetts; D008875:Middle Aged; D053580:Muscle Strength; D052097:Quadriceps Muscle / Q000502:physiology*
chemical_list: D004044:Dietary Proteins
keywords: animal protein; leg lean mass; plant protein; protein intake; quadriceps strength