Correlation between physiological and biochemical variables during short term adequate protein intake combined with resistance exercise in sedentary adults

Abstract

This study aimed to clarify the pure synergistic effect of an adequate protein intake (1.5 g/kg body weight/day) and resistance exercise (RE) on muscle strength, body composition, and metabolic markers in sedentary adults, excluding confounders arising from excessive protein intake or impaired protein turnover. A double-blind randomized controlled trial was performed on apparently healthy sedentary adult participants (n = 34). RE was performed for 4 weeks in the placebo (PLA-EX, n = 17) and whey protein supplement groups (PRO-EX, n = 17). Body composition, isokinetic muscular function, resting metabolic rate, blood biochemical variables, and liver ultrasound findings were analyzed and compared before and after the intervention. Both the PLA-EX and PRO-EX groups experienced significantly reduced body weight (PLA-EX, p < 0.001; PRO-EX, p < 0.01), body mass index (PLA-EX, p < 0.01; PRO-EX, p < 0.01), and body fat percentage (PLA-EX, p < 0.01; PRO-EX, p < 0.0001) after the intervention. In addition, serum adiponectin (PLA-EX, p < 0.0001; PRO-EX, p < 0.001), leptin (PLA-EX, p < 0.05; PRO-EX, p < 0.0001), growth/differentiation factor 8 (PLA-EX, p < 0.05; PRO-EX, p < 0.01), albumin (PLA-EX, p < 0.05; PRO-EX, p < 0.01), total cholesterol (PLA-EX, p < 0.001; PRO-EX, p < 0.0001), triglycerides (PLA-EX, p < 0.0001; PRO-EX, p < 0.0001), and controlled attenuation parameters measured by liver ultrasound were significantly decreased (PLA-EX, p < 0.05; PRO-EX, p < 0.0001). The PRO-EX group showed no significant difference in circulating free fatty acid levels before and after the intervention, whereas PLA-EX levels decreased after the intervention (p < 0.01). Muscle mass (p < 0.05), muscle strength (p < 0.001), and insulin-like growth factor 1 (p < 0.05) were significantly increased by the intervention in the PRO-EX group but not in the PLA-EX group. Testosterone (p < 0.01), high-density lipoprotein cholesterol (p < 0.01), aspartate aminotransferase (p < 0.0001), and alanine aminotransferase (p < 0.001) were significantly reduced in the PRO-EX group but not in the PLA-EX group. The combination of RE and adequate protein intake (1.5 g/kg body weight/day) synergistically increased fat metabolism, induced an increase in IGF-1 in the blood, and increased muscle mass and strength in sedentary adults.