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UBC Theses and Dissertations

The association between different levels of protein intake per day and muscle strength and skeletal muscle mass depending on sex, age, and physical activity level in young and middle-aged adults Gaytan Gonzalez, Saul Alejandro


Background: A protein intake above the recommended dietary allowance (RDA) (i.e., 0.8 g∙kgˉ¹∙dayˉ¹) might benefit muscle strength (MS) and skeletal muscle mass (SMM). However, whether a higher protein intake would benefit MS and SMM (depending on sex, age group, and physical activity level) at younger ages is still to be determined. Objective: To examine whether a protein intake above the RDA is associated with a higher MS and SMM depending on sex, age group, and physical activity level in young and middle-aged adults. Methods: A secondary data analysis from the National Health and Nutrition Examination Survey (NHANES) 2011-2014 was conducted. We analyzed data from participants aged 20 to 59, with dietary intake (24 h dietary recall), combined handgrip strength (HGS), dual-energy x-ray absorptiometry-derived appendicular lean soft tissue (ALST), accelerometer-assessed physical activity, among other variables (n = 3406). The protein intake was categorized as <0.8, 0.8 to 1.0, 1.0 to 1.6, and ≥1.6 g∙kgˉ¹∙dayˉ¹. HGS and ALST were adjusted for BMI (HGS-BMI, and ALST-BMI, respectively). Physical activity was categorized as low, moderate, and high. The HGS-BMI and ALST-BMI were compared among the protein intake groups, setting the 0.8 to 1.0 g∙kgˉ¹∙dayˉ¹ group as the reference. This analysis was carried out for the whole sample, by sex (males, females), age group (young, middle-aged), physical activity level (low, moderate, high), and their corresponding 12 subgroups in one model adjusted for confounding variables per outcome variable. Results: Protein intake per day was positively associated with MS in almost all the subgroups (11 out of 12, p < 0.05), whereas it was associated with SMM in half of the subgroups (7 out of 12), mainly in males (5 out of 6). Overall, the proportional benefit observed with a higher protein intake was greater in MS (≈30% vs the reference group), and it began to be observed at lower doses (starting at 1.0 g∙kgˉ¹∙dayˉ¹) than in SMM (≈10% vs the reference group), which was evident above 1.6 g∙kgˉ¹∙dayˉ¹. Conclusions: A slightly high protein intake (>1.0 g∙kgˉ¹∙dayˉ¹) was associated with a higher MS, while higher protein amounts (≥1.6 g∙kgˉ¹∙dayˉ¹) would be necessary to observe a higher SMM.

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