Dietary protein is associated with musculoskeletal health independently of dietary pattern: the Framingham Third Generation Study

Background: Above-average dietary protein, as a single nutrient, improves musculoskeletal health. Evaluating the link between dietary protein and musculoskeletal health from a whole-diet perspective is important, as dietary guidelines focus on dietary patterns. Objective: We examined the prospective association of novel dietary protein food clusters (derived from established dietary pattern techniques) with appendicular lean mass (ALM), quadriceps strength (QS), and bone mineral density (BMD) in 2986 men and women, aged 19-72 y, from the Framingham Third Generation Study. Design: Total protein intake was estimated by food-frequency questionnaire in 2002-2005. A cluster analysis was used to classify participants into mutually exclusive groups, which were determined by using the percentage of contribution of food intake to overall protein intake. General linear modeling was used to 1) estimate the association between protein intake (grams per day) and BMD, ALM, appendicular lean mass normalized for height (ALM/ht(2)), and QS (2008-2011) and to 2) calculate adjusted least-squares mean outcomes across quartiles of protein (grams per day) and protein food clusters. Results: The mean +/- SD age of subjects was 40 +/- 9 y; 82% of participants met the Recommended Daily Allowance (0.8 g center dot kg body weight(-1) center dot d(-1)). The following 6 dietary protein food clusters were identified: fast food and full-fat dairy, fish, red meat, chicken, low-fat milk, and legumes. BMD was not different across quartiles of protein intake (P-trend range = 0.32-0.82); but significant positive trends were observed for ALM, ALM/ht(2) (P < 0.001), and QS (P = 0.0028). Individuals in the lowest quartile of total protein intake (quartile 1) had significantly lower ALM, ALM/ht(2), and QS than did those in the higher quartiles of intake (quartiles 2-4; (P ranges = 0.0001-0.003, 0.0007-0.003, and 0.009-0.05, respectively). However, there were no associations between protein clusters and any musculoskeletal outcome in adjusted models. Conclusions: In a protein-replete cohort of adults, dietary protein is associated with ALM and QS but not with BMD. In this study, dietary protein food patterns do not provide further insight into beneficial protein effects on muscle outcomes.