Macro partitioning
Supplementing with whey protein, soy protein, or isolated leucine (standardized to ~3g leucine per serving) provides no additional benefit for increasing skeletal muscle mass or strength compared to a placebo when combined with resistance training in previously untrained college-aged males who already consume adequate protein (>1.3 g/kg/day) and increase caloric intake.
If you are a beginner lifter eating enough protein (over 1.3g/kg/day) and eating enough calories to support training, you do not need to spend extra money on whey, soy, or leucine supplements. They will not help you build more muscle or strength compared to a placebo, as long as your total diet is sufficient. Focus on your training and total food intake first.
In summary, LEU or protein supplementation (standardized to LEU content) does not provide added benefit in increasing whole-body skeletal muscle mass or strength above PLA following 3 months of training in previously untrained college-aged males that increase Calorie intakes with resistance training and consume above the recommended daily intake of protein throughout training.
Why this rating
Double-blind, placebo-controlled, randomized trial with adequate sample size (n=75) and standardized protocols, though limited to untrained young males.
Source
Effects of Whey, Soy or Leucine Supplementation with 12 Weeks of Resistance Training on Strength, Body Composition, and Skeletal Muscle and Adipose Tissue Histological Attributes in College-Aged Males
C. Brooks Mobley et al. · Nutrients · 2017
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