Relationship between different protein intake recommendations with muscle mass and muscle strength

Objective The purpose of the present study was to examine the relationship between two different levels of protein intake (0.8 vs. 1.2 g/kg body weight/day) with muscle mass and muscle strength. Method Seventy-two postmenopausal women were recruited. Body composition (bioelectrical impedance analysis), muscle strength (dynamometer), energy metabolism (indirect calorimetry) and dietary intake (dietary journal) were measured. We divided the women into two groups. Women with a protein intake of >= 1.2 g/kg body weight/day were placed in the Protein >= 1.2 group (n = 35), whereas women with a protein intake of 0.8-1.19 g/kg body weight/day were categorized in the Protein 0.8-1.19 group (n = 32). Results No significant difference was observed between groups for age, height, skeletal muscle mass, resting energy expenditure, total energy expenditure, carbohydrate and lipid intake. Significant differences between groups were observed for body mass index (p < 0.001), fat mass (p < 0.001) and muscle strength (hand grip and knee extensors) (p < 0.001). More specifically, the Protein >= 1.2 group presented a higher muscle strength as well as a lower body mass index and fat mass compared to the Protein 0.8-1.19 group. In addition, the group with a protein intake of >= 1.2 g/kg body weight/day presented significantly higher energy intake (p = 0.002), and essential (p < 0.001) and non-essential (p < 0.001) amino acid intake. Interestingly, when muscle strength was adjusted for essential or non-essential amino acids, differences in muscle strength persisted. Conclusion The present study indicates higher levels of muscle strength in postmenopausal women with a protein intake of >= 1.2 g/kg body weight/day compared to 0.8-1.19 g/kg body weight/day despite no differences in muscle mass.