Study analysis · Journal of the American College of Nutrition · 2013
Whey protein builds 80% more muscle than soy—here's why sugar drinkers still beat them both.
Drinking whey protein while lifting weights makes you gain more muscle than drinking soy or sugar, even if you eat the same calories.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study gave different drinks to people doing weight training and saw who gained more muscle. Because they randomly picked who got which drink, we can guess the drink might have caused the difference — but we’re not 100% sure because we don’t know if everyone was blind to what they were drinking.
What’s the bottom line?
People who drank whey protein while lifting weights gained more muscle than those who drank soy protein or sugar drinks, even when they ate the same number of calories.
How strong is this study?
The study is pretty good because it randomly assigned people and tracked them for months — that’s like a fair test. But we don’t know if the researchers or participants knew who got which drink, which could mess up the results. So it’s a strong hint, but not a perfect answer.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
63 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=63)+5.4/20
- Follow-up+10/10
100 / 100
23 / 100
- P-values+15/15
- Effect sizeno effect size reported
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 548 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
This design can establish causation. Randomization is explicitly stated in the abstract, allowing causal inference, but lack of blinding information introduces potential bias that may weaken the strength of causation.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding information were disclosed in the provided text.
The study lacks any declared funding sources or conflict of interest disclosures. While the results suggest a benefit of whey protein, the absence of transparency about funding or author affiliations limits the ability to assess potential bias.
Key takeaways
- 01
Whey group gained 3.3 kg of muscle; soy group gained 1.8 kg; sugar group gained 2.3 kg.
- 02
Whey raised blood leucine levels more than twice as much as the others.
- 03
Yes — gaining over 3 kg more muscle than the sugar group in 9 months is a meaningful difference for someone training hard.
Surprising findings
- Soy protein led to the least muscle gain despite matching whey’s protein dose.Many plant-based athletes believe soy is equivalent to whey for muscle building—this study contradicts that assumption.
Practical takeaways
If you're serious about building muscle with resistance training, choose whey protein over soy or carb-based supplements.
This study used supervised training and specific dosing—results may vary with home workouts or uncontrolled diets.
low confidenceWhy this study matters
Whey Beats Soy by a Mile
Participants who took whey protein gained 3.3 ± 1.5 kg of lean body mass over 9 months, while soy protein users gained only 1.8 ± 1.6 kg—despite both providing the same daily protein intake of 1.4 g/kg.
Most people think all proteins are equal for muscle building—this shows the source matters more than just the amount.
Carbs Beat Soy—But Lose to Whey
The carbohydrate group gained 2.3 ± 1.7 kg of lean mass—more than soy but less than whey—even though they consumed only 1.1 g/kg of protein daily.
This suggests even low-protein diets can build muscle with training, but whey pushes it to another level.
Leucine Is the Secret Sauce
Whey raised fasting leucine levels by 20% and post-exercise leucine more than twofold compared to soy or carbs—and these spikes correlated directly with muscle gains.
Leucine isn’t just another amino acid—it’s the trigger that tells your muscles to grow, and whey delivers it better than anything else.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
People who drank whey protein while lifting weights gained more muscle than those who drank soy protein or sugar drinks, even when they ate the same number of calories.
Research results
Whey group gained 3.3 kg of muscle; soy group gained 1.8 kg; sugar group gained 2.3 kg. Whey raised blood leucine levels more than twice as much as the others.
What this means - more context
Yes — gaining over 3 kg more muscle than the sugar group in 9 months is a meaningful difference for someone training hard.
To determine whether whey protein supplementation promotes greater lean body mass gains than soy protein or carbohydrate during resistance training.
In a 9-month randomized trial, whey protein supplementation led to significantly greater lean body mass gains (3.3 ± 1.5 kg) compared to soy (1.8 ± 1.6 kg) or carbohydrate (2.3 ± 1.7 kg), despite similar caloric intake. Whey also caused higher fasting and postexercise plasma leucine levels, which correlated with muscle gains.
Methods Used
Randomized controlled trial with 63 untrained adults assigned to isocaloric supplements of carbohydrate (n=22), whey protein (n=19), or soy protein (n=22). All completed 96 supervised resistance training sessions over 9 months. Body composition and plasma amino acids were measured at baseline and 3, 6, and 9 months.
Main Finding
Whey protein supplementation resulted in significantly greater lean body mass gains (3.3 ± 1.5 kg) than soy (1.8 ± 1.6 kg) or carbohydrate (2.3 ± 1.7 kg), with fasting and postexercise leucine levels elevated more with whey and positively correlated with lean mass gains.
Confidence Level
Limited - based on abstract only, full methodology not available
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Effect sizes reported but confidence intervals not mentioned
- •Blinding status unknown
Surprising Findings
Soy protein led to the least muscle gain despite matching whey’s protein dose.
Many plant-based athletes believe soy is equivalent to whey for muscle building—this study contradicts that assumption.
Practical Takeaways
If you're serious about building muscle with resistance training, choose whey protein over soy or carb-based supplements.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 548 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Human RCT
Subject
Moderate probability
on the GRADE evidence scale
This study gave different drinks to people doing weight training and saw who gained more muscle. Because they randomly picked who got which drink, we can guess the drink might have caused the difference — but we’re not 100% sure because we don’t know if everyone was blind to what they were drinking.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Explicit randomization
- Control groups for all conditions
- Long-term intervention (9 months)
Weaknesses
- Blinding status unknown
- Full methodology not available - based on abstract only
- No details on allocation concealment or dropout rates
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
People who drank whey protein while lifting weights gained more muscle than those who drank soy protein or sugar drinks, even when they ate the same number of calories.
Research results
Whey group gained 3.3 kg of muscle; soy group gained 1.8 kg; sugar group gained 2.3 kg. Whey raised blood leucine levels more than twice as much as the others.
What this means - more context
Yes — gaining over 3 kg more muscle than the sugar group in 9 months is a meaningful difference for someone training hard.
To determine whether whey protein supplementation promotes greater lean body mass gains than soy protein or carbohydrate during resistance training.
In a 9-month randomized trial, whey protein supplementation led to significantly greater lean body mass gains (3.3 ± 1.5 kg) compared to soy (1.8 ± 1.6 kg) or carbohydrate (2.3 ± 1.7 kg), despite similar caloric intake. Whey also caused higher fasting and postexercise plasma leucine levels, which correlated with muscle gains.
Methods Used
Randomized controlled trial with 63 untrained adults assigned to isocaloric supplements of carbohydrate (n=22), whey protein (n=19), or soy protein (n=22). All completed 96 supervised resistance training sessions over 9 months. Body composition and plasma amino acids were measured at baseline and 3, 6, and 9 months.
Main Finding
Whey protein supplementation resulted in significantly greater lean body mass gains (3.3 ± 1.5 kg) than soy (1.8 ± 1.6 kg) or carbohydrate (2.3 ± 1.7 kg), with fasting and postexercise leucine levels elevated more with whey and positively correlated with lean mass gains.
Confidence Level
Limited - based on abstract only, full methodology not available
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Effect sizes reported but confidence intervals not mentioned
- •Blinding status unknown
Surprising Findings
Soy protein led to the least muscle gain despite matching whey’s protein dose.
Many plant-based athletes believe soy is equivalent to whey for muscle building—this study contradicts that assumption.
Practical Takeaways
If you're serious about building muscle with resistance training, choose whey protein over soy or carb-based supplements.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 548 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Human RCT
Subject
Moderate probability
on the GRADE evidence scale
This study gave different drinks to people doing weight training and saw who gained more muscle. Because they randomly picked who got which drink, we can guess the drink might have caused the difference — but we’re not 100% sure because we don’t know if everyone was blind to what they were drinking.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Explicit randomization
- Control groups for all conditions
- Long-term intervention (9 months)
Weaknesses
- Blinding status unknown
- Full methodology not available - based on abstract only
- No details on allocation concealment or dropout rates
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study is pretty good because it randomly assigned people and tracked them for months — that’s like a fair test. But we don’t know if the researchers or participants knew who got which drink, which could mess up the results. So it’s a strong hint, but not a perfect answer.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
63 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=63)+5.4/20
- Follow-up+10/10
100 / 100
23 / 100
- P-values+15/15
- Effect sizeno effect size reported
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 548 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
This design can establish causation. Randomization is explicitly stated in the abstract, allowing causal inference, but lack of blinding information introduces potential bias that may weaken the strength of causation.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding information were disclosed in the provided text.
The study lacks any declared funding sources or conflict of interest disclosures. While the results suggest a benefit of whey protein, the absence of transparency about funding or author affiliations limits the ability to assess potential bias.
Standing
Who’s using this study?
The videos and claims on this site that lean on this study, and the researchers who wrote it.
1 video from Shawn Baker MD cite this study, drawing 1 claim from it.
- Very strong evidence
Randomized or controlled trials support this claim, alongside consistent supporting evidence.
Evidence
Authored by
22 researchersIf this is your work, this is how we attribute it on Fit Body Science. Jeff S. Volek is listed as the lead author.