Study analysis · The FASEB Journal · 2016
This 2g amino acid in your snack made women 14% fuller—but 3g did nothing, even though blood levels spiked 260%.
Adding 2 grams of a protein part called leucine to a small snack made women feel fuller, but adding more didn’t help—and didn’t make them less hungry.
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 40 women different snack bars and asked how full they felt afterward. It found that one bar with extra leucine made them feel a little fuller — but only for a short time. It doesn't prove that eating this bar will help people eat less or lose weight — it just shows a small, quick change in how they felt after eating.
What’s the bottom line?
Scientists tested if adding different amounts of a protein part called leucine to small snacks makes people feel fuller or less hungry.
How strong is this study?
The study tried to be fair by randomly giving out bars and not telling the women or researchers which bar was which — that’s good! But it only had 40 people, and we can’t see all the details because the full study isn’t available. So while it’s well-designed on paper, we can’t be totally sure the results are reliable without seeing everything.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
67 / 100
- Randomization+20/20
- Blinding+15/15
- Control group+15/15
- Sample size (n=40)+3.6/20
- Follow-upno follow-up reported
100 / 100
54 / 100
- P-values+15/15
- Effect size+20/20
- 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 557 / 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. The study is explicitly described as a double-blind, randomized controlled trial with a control group, which allows for causal inference. However, the small sample size (n=40) and pilot nature limit the strength of this inference.
Key takeaways
- 01
With 2g leucine, fullness went up by 14.2%.
- 02
With 3g leucine, blood leucine spiked 260% but fullness didn't go up more.
- 03
Hunger didn't change at any dose.
- 04
Feeling 14% fuller after one snack might help reduce snacking later, but it didn't make people less hungry.
Surprising findings
- A 260% spike in plasma leucine with 3g did not increase fullness beyond the 2g dose.It’s counterintuitive—more of a substance that triggers fullness should logically have a stronger effect, but here, biology hit a plateau.
Practical takeaways
If you're trying to feel fuller on a low-calorie snack, look for products with ~2g of leucine peptide (like PepForm®) in a 180-calorie bar.
This was tested only in healthy women; results may not apply to men, children, or people with metabolic conditions.
low confidenceWhy this study matters
2g Leucine = 14% Fuller
In a double-blind trial with 40 women, a 180-kcal nutrition bar with 2g of leucine peptide increased fullness by 14.2% (iAUC, p=0.04) compared to a bar with 0g leucine. This effect was statistically significant.
Most people think more protein = more fullness, but here, just 2g of one amino acid—less than a teaspoon—had a measurable effect on satiety without extra calories.
3g Leucine Spikes Blood Levels—But Not Fullness
The 3g leucine bar caused a 260% increase in peak plasma leucine (Cmax) compared to 0g, yet fullness didn’t improve beyond the 2g dose. Hunger remained unchanged across all doses.
It defies the ‘more is better’ assumption—your body can soak up way more leucine, but it doesn’t translate to feeling fuller. This suggests a biological ceiling.
Leucine Affects Fullness, Not Hunger
Despite changes in fullness, hunger ratings showed no significant difference across 0g, 2g, or 3g leucine doses. This suggests leucine may influence satiety signals differently than appetite.
Most people confuse hunger and fullness—this study shows they can be regulated separately. You might feel satisfied without feeling less hungry.
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
Scientists tested if adding different amounts of a protein part called leucine to small snacks makes people feel fuller or less hungry.
Research results
With 2g leucine, fullness went up by 14.2%. With 3g leucine, blood leucine spiked 260% but fullness didn't go up more. Hunger didn't change at any dose.
What this means - more context
Feeling 14% fuller after one snack might help reduce snacking later, but it didn't make people less hungry.
To determine if acute leucine supplementation in low-protein nutrition bars affects satiety (fullness and hunger) and plasma leucine levels in healthy women.
In a double-blind RCT crossover trial with 40 women, a 2g leucine peptide (LP) bar increased fullness iAUC by 14.2% (p=0.04) compared to 0g LP, but 3g LP did not further increase fullness despite a 260% higher peak plasma leucine (Cmax). Hunger ratings were unchanged across all doses.
Methods Used
Double-blind, randomized crossover trial; 40 healthy women consumed three 180-kcal isocaloric nutrition bars (0g, 2g, or 3g leucine peptide) after overnight fast; fullness and hunger measured via Visual Analog Scales (VAS); plasma leucine quantified by GC-qMS.
Main Finding
A 2g leucine peptide bar significantly increased post-prandial fullness by 14.2% (iAUC, p=0.04) compared to 0g LP; 3g LP increased peak plasma leucine by 260% (Cmax, p<0.0001) but did not significantly increase fullness compared to 0g LP; no significant effect on hunger.
Confidence Level
Limited - based on abstract only, full methodology not available
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Funded by PepsiCo Global R&D - potential conflict of interest
- •Pilot study with small sample size (n=40) and limited generalizability (only women)
Surprising Findings
A 260% spike in plasma leucine with 3g did not increase fullness beyond the 2g dose.
It’s counterintuitive—more of a substance that triggers fullness should logically have a stronger effect, but here, biology hit a plateau.
Practical Takeaways
If you're trying to feel fuller on a low-calorie snack, look for products with ~2g of leucine peptide (like PepForm®) in a 180-calorie bar.
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 557 / 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 40 women different snack bars and asked how full they felt afterward. It found that one bar with extra leucine made them feel a little fuller — but only for a short time. It doesn't prove that eating this bar will help people eat less or lose weight — it just shows a small, quick change in how they felt after eating.
Strengths
- Explicitly described as double-blind, randomized, crossover RCT
- Control group used
- Objective biomarker measurement (plasma leucine via GC-qMS)
Weaknesses
- Small sample size (n=40)
- Pilot study designation
- Abstract only — full methodology not verifiable
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists tested if adding different amounts of a protein part called leucine to small snacks makes people feel fuller or less hungry.
Research results
With 2g leucine, fullness went up by 14.2%. With 3g leucine, blood leucine spiked 260% but fullness didn't go up more. Hunger didn't change at any dose.
What this means - more context
Feeling 14% fuller after one snack might help reduce snacking later, but it didn't make people less hungry.
To determine if acute leucine supplementation in low-protein nutrition bars affects satiety (fullness and hunger) and plasma leucine levels in healthy women.
In a double-blind RCT crossover trial with 40 women, a 2g leucine peptide (LP) bar increased fullness iAUC by 14.2% (p=0.04) compared to 0g LP, but 3g LP did not further increase fullness despite a 260% higher peak plasma leucine (Cmax). Hunger ratings were unchanged across all doses.
Methods Used
Double-blind, randomized crossover trial; 40 healthy women consumed three 180-kcal isocaloric nutrition bars (0g, 2g, or 3g leucine peptide) after overnight fast; fullness and hunger measured via Visual Analog Scales (VAS); plasma leucine quantified by GC-qMS.
Main Finding
A 2g leucine peptide bar significantly increased post-prandial fullness by 14.2% (iAUC, p=0.04) compared to 0g LP; 3g LP increased peak plasma leucine by 260% (Cmax, p<0.0001) but did not significantly increase fullness compared to 0g LP; no significant effect on hunger.
Confidence Level
Limited - based on abstract only, full methodology not available
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Funded by PepsiCo Global R&D - potential conflict of interest
- •Pilot study with small sample size (n=40) and limited generalizability (only women)
Surprising Findings
A 260% spike in plasma leucine with 3g did not increase fullness beyond the 2g dose.
It’s counterintuitive—more of a substance that triggers fullness should logically have a stronger effect, but here, biology hit a plateau.
Practical Takeaways
If you're trying to feel fuller on a low-calorie snack, look for products with ~2g of leucine peptide (like PepForm®) in a 180-calorie bar.
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 557 / 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 40 women different snack bars and asked how full they felt afterward. It found that one bar with extra leucine made them feel a little fuller — but only for a short time. It doesn't prove that eating this bar will help people eat less or lose weight — it just shows a small, quick change in how they felt after eating.
Strengths
- Explicitly described as double-blind, randomized, crossover RCT
- Control group used
- Objective biomarker measurement (plasma leucine via GC-qMS)
Weaknesses
- Small sample size (n=40)
- Pilot study designation
- Abstract only — full methodology not verifiable
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study tried to be fair by randomly giving out bars and not telling the women or researchers which bar was which — that’s good! But it only had 40 people, and we can’t see all the details because the full study isn’t available. So while it’s well-designed on paper, we can’t be totally sure the results are reliable without seeing everything.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
67 / 100
- Randomization+20/20
- Blinding+15/15
- Control group+15/15
- Sample size (n=40)+3.6/20
- Follow-upno follow-up reported
100 / 100
54 / 100
- P-values+15/15
- Effect size+20/20
- 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 557 / 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. The study is explicitly described as a double-blind, randomized controlled trial with a control group, which allows for causal inference. However, the small sample size (n=40) and pilot nature limit the strength of this inference.
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 Physionic cite this study, drawing 2 claims from it.