Post-Exercise Whey Protein Supplementation: Effects on IGF-1, Strength, and Body Composition in Pre-Menopausal Women, a Randomised Controlled Trial

<b>Introduction:</b> The purpose of this study was to evaluate effects of post-exercise protein supplementation with combined resistance and interval training on total insulin-like growth factor-1 (IGF-1) concentration, strength (3RM), and body composition (DXA) in untrained pre-menopausal women. <b>Methods</b>: Twenty-seven women (33.6 ± 9.2 years, 69.4 ± 12.4 kg, 25.5 ± 3.7 kg/m²) were randomised into a control (CON) or moderate protein group (PRO) (3 g, 24 g, resp.) and completed twelve weeks of upper-body resistance (2×/week) and high-intensity interval cycle training (3×/week). Linear mixed-effects model analyses were conducted. <b>Results</b>: PRO had a greater daily protein intake (5.0 ± 16.6 g, 20.5 ± 13.9 g, CON, PRO, resp., <i>p</i> = 0.025), with no change in IGF-1 (-6.0 ± 27.7 µg/L, -2.1 ± 27.8 µg/L, CON, PRO, resp., <i>p</i> = 0.920). Total lean mass increased (0.84 ± 0.80 kg, 0.56 ± 1.4 kg, CON, PRO, resp., <i>p</i> = 0.009), and all strength measures increased in both groups (19-113%, <i>p</i> < 0.05). <b>Conclusions</b>: Untrained women can increase strength and lean mass over twelve weeks of combined resistance and interval training. Post-exercise protein supplementation had little effect, despite increasing protein intake by ~20 g/day in the PRO group. IGF-1 was not associated with any outcome measure.