Study analysis · Clinical nutrition · 2018
This supplement made frail older women gain over 1.7 kg of muscle in just 3 weeks—but only women.
Older women who took a daily amino acid supplement gained muscle and lost fat in three weeks, but the supplement didn't help men or improve how their bodies made protein.
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 some older people a supplement and others a fake one to see what happened. Because they were randomly assigned, we can guess the supplement might have caused the changes—but we’re not super sure because not everyone was hidden from knowing which one they got.
What’s the bottom line?
Older women who were malnourished took a daily amino acid supplement called citrulline for 3 weeks. Researchers checked if it helped them build muscle or lose fat.
How strong is this study?
The study tried to be fair by randomly giving out pills, which is good. But it only had 24 people, and we can’t see all the details—so it’s like doing a science experiment with just a few friends and no notebook. That makes it harder to trust the results fully.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
59 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=24)+2.3/20
- 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 546 / 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 was explicitly stated, allowing causal inference, but blinding was unknown and sample size was small (n=24), which limits precision and increases risk of chance findings.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding statements were disclosed in the provided text; all authors appear to be affiliated with academic or public health institutions without industry ties.
The study appears to be conducted by academic and public hospital institutions in France with no disclosed industry funding or author affiliations with commercial entities. However, the absence of a formal COI or funding statement limits certainty; absence of disclosure does not confirm absence of conflict.
Key takeaways
- 01
Women who took citrulline gained 1.7 kg of lean mass and 1.1 kg of muscle in their arms and legs, and lost 1.3 kg of fat.
- 02
The supplement did not change protein synthesis rates in the body or liver.
- 03
Gaining over 1.5 kg of muscle and losing over 1 kg of fat in just 3 weeks is a large change for very frail older adults and could improve mobility and strength.
Surprising findings
- Citrulline increased lean mass and decreased fat mass in women without increasing protein synthesis.It’s widely believed that muscle growth requires increased protein synthesis—yet here, muscle increased despite no change in synthesis rates.
Practical takeaways
Older women with malnutrition might consider citrulline supplementation under medical supervision, given the observed muscle gain and fat loss.
The study had only 24 participants, no pre-registration, and full methodology is unavailable. Effects may not be reproducible.
low confidenceWhy this study matters
Muscle Gain Only in Women
In women only, 10g/day of citrulline for 3 weeks increased lean mass by 1.7 kg and appendicular skeletal muscle mass by 1.1 kg, while reducing fat mass by 1.3 kg. These changes were statistically significant (p=0.016, p=0.018, p=0.001) but were not seen in the overall population or in men.
Most muscle-building supplements claim to work for everyone—but here, a dramatic change happened only in older women, raising questions about gender-specific biology in aging and nutrition.
No Boost in Protein Synthesis
Despite increasing amino acid availability, citrulline had no effect on whole-body or liver protein synthesis rates. This contradicts the hypothesis that citrulline stimulates muscle building by boosting protein production.
It’s surprising that more amino acids in the blood didn’t lead to more muscle protein being made—suggesting muscle growth may happen through other, unknown pathways.
Subgroup Analysis Red Flag
The positive effects were only found in a subgroup of 18 women out of 24 total participants, and this analysis was not pre-specified—raising concerns about statistical reliability.
A dramatic result in a tiny subgroup could be a fluke—especially when the main study population showed no effect.
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
Older women who were malnourished took a daily amino acid supplement called citrulline for 3 weeks. Researchers checked if it helped them build muscle or lose fat.
Research results
Women who took citrulline gained 1.7 kg of lean mass and 1.1 kg of muscle in their arms and legs, and lost 1.3 kg of fat. The supplement did not change protein synthesis rates in the body or liver.
What this means - more context
Gaining over 1.5 kg of muscle and losing over 1 kg of fat in just 3 weeks is a large change for very frail older adults and could improve mobility and strength.
To assess the effects of 3-week oral L-citrulline supplementation (10 g/day) on protein metabolism and body composition in malnourished older adults aged 80–92 years.
Citrulline supplementation increased systemic amino acid availability compared to an isonitrogenous placebo but had no effect on whole-body or liver protein synthesis. In women only, citrulline significantly increased lean mass (+1.7 kg) and appendicular skeletal muscle mass (+1.1 kg) and decreased fat mass (−1.3 kg). No significant changes in these outcomes were observed in the overall population.
Methods Used
Prospective randomized multicenter trial with 24 malnourished older adults (18 women, 6 men; aged 80–92 years) receiving either 10 g/day of citrulline or an isonitrogenous placebo of non-essential amino acids for 3 weeks. Outcomes included whole-body and liver protein synthesis, splanchnic amino acid extraction, and body composition measures.
Main Finding
Citrulline supplementation significantly increased systemic amino acid availability (p < 0.05) and, in women only, increased lean mass (mean +1.7 kg, p = 0.016) and appendicular skeletal muscle mass (mean +1.1 kg, p = 0.018), while decreasing fat mass (mean −1.3 kg, p = 0.001). No significant effect on whole-body or liver protein synthesis was found.
Confidence Level
Limited - based on abstract only, full methodology not available
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Subgroup analysis (women only) not pre-specified and may be underpowered
- •Effect sizes reported only for subgroup, not overall population
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
Citrulline increased lean mass and decreased fat mass in women without increasing protein synthesis.
It’s widely believed that muscle growth requires increased protein synthesis—yet here, muscle increased despite no change in synthesis rates.
Practical Takeaways
Older women with malnutrition might consider citrulline supplementation under medical supervision, given the observed muscle gain and fat loss.
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 546 / 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 some older people a supplement and others a fake one to see what happened. Because they were randomly assigned, we can guess the supplement might have caused the changes—but we’re not super sure because not everyone was hidden from knowing which one they got.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Explicitly randomized design
- Controlled with isonitrogenous placebo
- Multicenter design
Weaknesses
- Blinding status unknown
- Very small sample size (n=24)
- Subgroup analyses (e.g., women only) not powered for primary inference
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Older women who were malnourished took a daily amino acid supplement called citrulline for 3 weeks. Researchers checked if it helped them build muscle or lose fat.
Research results
Women who took citrulline gained 1.7 kg of lean mass and 1.1 kg of muscle in their arms and legs, and lost 1.3 kg of fat. The supplement did not change protein synthesis rates in the body or liver.
What this means - more context
Gaining over 1.5 kg of muscle and losing over 1 kg of fat in just 3 weeks is a large change for very frail older adults and could improve mobility and strength.
To assess the effects of 3-week oral L-citrulline supplementation (10 g/day) on protein metabolism and body composition in malnourished older adults aged 80–92 years.
Citrulline supplementation increased systemic amino acid availability compared to an isonitrogenous placebo but had no effect on whole-body or liver protein synthesis. In women only, citrulline significantly increased lean mass (+1.7 kg) and appendicular skeletal muscle mass (+1.1 kg) and decreased fat mass (−1.3 kg). No significant changes in these outcomes were observed in the overall population.
Methods Used
Prospective randomized multicenter trial with 24 malnourished older adults (18 women, 6 men; aged 80–92 years) receiving either 10 g/day of citrulline or an isonitrogenous placebo of non-essential amino acids for 3 weeks. Outcomes included whole-body and liver protein synthesis, splanchnic amino acid extraction, and body composition measures.
Main Finding
Citrulline supplementation significantly increased systemic amino acid availability (p < 0.05) and, in women only, increased lean mass (mean +1.7 kg, p = 0.016) and appendicular skeletal muscle mass (mean +1.1 kg, p = 0.018), while decreasing fat mass (mean −1.3 kg, p = 0.001). No significant effect on whole-body or liver protein synthesis was found.
Confidence Level
Limited - based on abstract only, full methodology not available
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Subgroup analysis (women only) not pre-specified and may be underpowered
- •Effect sizes reported only for subgroup, not overall population
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
Citrulline increased lean mass and decreased fat mass in women without increasing protein synthesis.
It’s widely believed that muscle growth requires increased protein synthesis—yet here, muscle increased despite no change in synthesis rates.
Practical Takeaways
Older women with malnutrition might consider citrulline supplementation under medical supervision, given the observed muscle gain and fat loss.
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 546 / 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 some older people a supplement and others a fake one to see what happened. Because they were randomly assigned, we can guess the supplement might have caused the changes—but we’re not super sure because not everyone was hidden from knowing which one they got.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Explicitly randomized design
- Controlled with isonitrogenous placebo
- Multicenter design
Weaknesses
- Blinding status unknown
- Very small sample size (n=24)
- Subgroup analyses (e.g., women only) not powered for primary inference
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study tried to be fair by randomly giving out pills, which is good. But it only had 24 people, and we can’t see all the details—so it’s like doing a science experiment with just a few friends and no notebook. That makes it harder to trust the results fully.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
59 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=24)+2.3/20
- 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 546 / 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 was explicitly stated, allowing causal inference, but blinding was unknown and sample size was small (n=24), which limits precision and increases risk of chance findings.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding statements were disclosed in the provided text; all authors appear to be affiliated with academic or public health institutions without industry ties.
The study appears to be conducted by academic and public hospital institutions in France with no disclosed industry funding or author affiliations with commercial entities. However, the absence of a formal COI or funding statement limits certainty; absence of disclosure does not confirm absence of conflict.
Standing
The people behind it
The researchers who wrote the study this analysis is built on.
Authored by
18 researchersIf this is your work, this is how we attribute it on Fit Body Science. O. Bouillanne is listed as the lead author.