Protein intake, physical activity, and skeletal muscle outcomes in middle-aged adults: an observational study from...

Sarcopenia, the age-related decline in muscle mass and strength is a growing challenge for older adults. This study investigates whether meeting the WHO physical activity guidelines (150-300 min/week of moderate or 75 min/week of vigorous exercise) with higher protein intake, based on the RDA, is associated with appendicular lean soft tissue index (ALSTI) and handgrip strength (HGS) in adults living in the United States aged 40-59 years. Data from the National Health and Nutrition Examination Survey 2007-2020 included 2540 adults aged ≥40 years. Physical activity (moderate/vigorous) was self-reported, while higher protein intake was assessed via two 24-hour recalls (>0.8 g/kg/bodyweight). Linear regressions, adjusted for age, sex, BMI, race, education, comorbidities, and energy-adjusted protein intake were used to assess associations with ALSTI and HGS. In fully adjusted models, vigorous activity with higher protein intake (47.1 ± 5.6 years) was associated with ALSTI only after adjustments for age, sex, BMI, race, education (β = 0.37, SE 0.17, p = 0.047; mean baseline: 8.56 ± 1.67 kg/m²). No associations were found in the fully adjusted model for ALSTI (p = 0.31), and across all models for HGS (mean baseline: 43.6 ± 10.1 kg). Moderate activity with higher protein intake was not associated with HGS or ALSTI across adjusted models. Meeting vigorous or moderate-intensity activity guidelines with higher than the RDA protein intake was not associated with ALSTI or HGS in middle-aged US adults.