Research
Macro partitioning
Soy protein supplementation may blunt the acute post-exercise testosterone response compared to whey protein or placebo, although it does not necessarily lower resting total testosterone.
Soy protein is safe and does not lower your baseline testosterone. However, if you want to maximize the acute testosterone spike after heavy lifting, whey protein might be a slightly better choice than soy. For general health and muscle building, either is fine.
ModerateQualifiesMEDIUM confidence
Additionally, testosterone concentrations were significantly lower during SPS compared to both WPS and PLA during the post-exercise period. ... The results from these studies do not provide any conclusive evidence regarding soy protein having a negative effect on testosterone production. However, they are consistent in demonstrating that whey protein supplementation may be the superior protein supplement for enhancing the testosterone response to training.
Why this rating
Studies are small (n=10-15) and mixed; meta-analyses show no effect on resting T, but acute studies show blunted response.
Source
Manipulation of Dietary Intake on Changes in Circulating Testosterone Concentrations
Amit Zamir et al. · Nutrients · 2021
DOI 10.3390/nu13103375
narrative_reviewCited 23×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
More from this paper
- Maintaining energy availability above 30 kcal/kg fat-free mass per day is required to prevent significant reductions in circulating testosterone; deficits below this threshold suppress luteinizing hormone (LH) and subsequently lower testosterone.Good
- High-fat diets (specifically ketogenic diets with >75% fat) increase total and free testosterone in resistance-trained men compared to Western diets, likely due to higher cholesterol intake supporting steroidogenesis.Moderate
Related findings · Macro partitioning
- Total daily protein intake of 1.6 g/kg/day is sufficient for maximizing resistance training-induced muscle gains, with an upper confidence interval of 2.2 g/kg/day.Strong
- Resistance exercise training combined with sufficient dietary protein intake acts synergistically to maximize skeletal muscle hypertrophy, with protein intake saturating around 1.6 g/kg/day for general populations and potentially requiring 2.0-2.2 g/kg/day for resistance-trained individuals.Strong
- Trans fats should be completely eliminated from the diet, as they increase LDL cholesterol, decrease HDL cholesterol, and are directly associated with increased coronary risk.Strong
This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →