Intake of whey isolate supplement and muscle mass gains in young healthy adults when combined with resistance training: a blinded randomized clinical trial (pilot study).
Level 2 - randomized trial
Individual randomized trial
PubMed 31565912 · doi:10.23736/S0022-4707.19.09741-X
What was done
Eight resistance-trained young adults (men and women aged 18–30) were randomized in a blinded pilot study to receive either whey protein isolate (n=4) or an isocaloric placebo (n=4) during a 12-week resistance training program. Ultrasound was used to measure muscle thickness of the biceps brachii (at 67% length) and quadriceps muscles (vastus lateralis, vastus intermedius, rectus femoris at 30% and 50% length). Muscle strength was assessed via isokinetic peak torque on a dynamometer at 60°/s and 180°/s for knee and elbow flexors/extensors. Lean body mass and body fat percentage were assessed by segmental multi-frequency bioelectrical impedance before and after the intervention.
What was found
Resistance training significantly increased muscle thickness across all sites except vastus lateralis and rectus femoris at 30% length (P>0.05). Whey protein intake was associated with a significant increase in vastus intermedius thickness at 50% length (P=0.045) and a non-significant trend at 30% length (P=0.075). Peak torque increased with resistance training across all knee flexors/extensors and for elbow flexors/extensors at 60° extension and 180° flexion (P<0.05), with no effect from whey protein. Lean body mass increased overall (P=0.015) and body fat percentage remained stable (P>0.05), with no interaction between training and supplementation.
Why it matters
This pilot study suggests potential site-specific quadriceps hypertrophy with whey supplementation during resistance training, though it observed no additive effect on muscular strength in young resistance-trained adults.
Limits
The study is severely underpowered due to an extremely small sample size (n=8 total, 4 per group). The abstract does not specify the supplement dosage, total dietary protein intake, or sex-stratified outcomes, and bioelectrical impedance was used rather than dual-energy X-ray absorptiometry for body composition.
Cited by
- supports Twenty grams of whey protein contains approximately 2 to 2.5 grams of leucine.