A Dietary Supplement Containing Essential Amino Acids in Combination with Resistance Training Improves Body Composition and Physical Performance Parameters in Generally Healthy Adults: A Pragmatic Single Arm Study

Introduction: Essential amino acid (EAA) supplements are popular for increasing muscle mass and improving performance. Methods: This pragmatic single arm study enrolled 30 participants (17F/13M) to consume a commercially available supplement providing 3.6 g/d EAA + arginine and complete supervised strength training (two, upper-body days, two, lower body days/week) over a 10-week period. DXA body composition, muscular strength (1 repetition max [1RM]) muscular endurance (number of repetitions to failure), and the Acute Recovery and Stress Scale (ARSS) were assessed at baseline and week 10. Results: Participants (n=27 completers [15F/12M]; mean ± SD age 38.7 ± 8.6 y and BMI 29.4 ± 3.6 kg/m2) experienced statistically significant (p<0.05) reductions in total fat mass (-0.9 [-1.8, -0.1] kg) and visceral fat (-96 [-165, -26] g), with concurrent increases in total lean body mass (1.1 [0.4, 1.8] kg), upper body strength (~18% increase in bench press 1-RM), lower body strength (~40% increase in angled leg-press 1-RM), and muscular endurance (~75% increased repetitions to failure for both exercises). Additionally, participants demonstrated improvements in all stress and recovery outcomes within the ARSS. Conclusions: These results demonstrate the potential value of EAA supplementation as part of a comprehensive approach to support physical performance and body composition in previously untrained or recreationally trained adults.