Effect of whey vs. soy protein supplementation on recovery kinetics following speed endurance training in competitive male soccer players: a randomized controlled trial

Ten well-trained, healthy, competitive male soccer players (approx. 21 ± 1.5 years; height ~1.80 m; weight ~79.3 ± 6.8 kg). Randomized, double-blind, three-trial cross-over, repeated-measures design with Placebo, Whey Protein, and Soy Protein trials.

Adaptive 7-day period with individualized protein intake 0.8-1 g/kg/day; 7-day pre-loading with WP or SP to achieve 1.5 g/kg/day total protein (PL remains at 0.8-1 g/kg/day); 3-day experimental period with two speed-endurance training sessions 48 h apart; daily drinks (~500 ml) consumed with breakfast on non-training days and immediately post-training on training days; beverages contained whey protein isolate (WP) or soy protein isolate (SP) or isoenergetic maltodextrin (PL); protein content adjusted to reach 1.5 g/kg/day for WP/SP.

Increasing daily protein intake to 1.5 g/kg/day via whey or soy supplements mitigates field performance deterioration during consecutive speed-endurance training sessions, enabling greater high-intensity and high-speed running during the second session compared with placebo. 10 m sprint impairment at 24 h occurred only in placebo; CK and DOMS rose similarly across trials; SP showed faster protein-carbonyl recovery at 48 h (WP showed a non-significant trend). Authors conclude that WP and SP are equally effective in preserving field performance under congested training, and soy protein offers a cost-effective alternative to whey.

Small sample size (n=10); total energy and macronutrient intakes were below in-season recommendations; only male soccer players; short-term, two-session congested training; limited generalizability to longer training periods or other populations.