Study analysis · European Journal of Nutrition · 2022
Fasting two days a week works just as well as eating less every day for building muscle and losing fat—if you lift weights and eat enough protein.
Both diets helped people gain muscle and lose fat equally, but eating less every day built slightly more leg muscle.
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 watched two groups of people while they followed different diet plans along with strength training. It can show that both groups changed in similar ways, but it can't prove that the diets caused those changes because the groups weren't set up perfectly fairly.
What’s the bottom line?
This study tested two diets—eating less every day or fasting two days a week—while doing strength training and eating enough protein.
How strong is this study?
The study did some things well, like measuring muscles with special machines and guiding people through workouts. But it didn’t hide who was in which group, and people knew what diet they were on, which can affect results. That makes us less confident that the differences (or similarities) were truly because of the diets.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
35 / 100
- Randomizationrandomization unclear
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=34)+3.1/20
- Follow-up+10/10
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registration+15/15
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 552 / 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 cannot establish causation — the findings describe an association, not a cause. Randomization is described as 'coin toss' with no allocation concealment, making it unclear and not meeting RCT criteria per rules. Blinding status is unknown. Therefore, despite initial classification as RCT, it fails key methodological criteria and must be downgraded to cohort study.
Key takeaways
- 01
Both groups gained 3.7% muscle, lost 4.6% weight and 24.1% fat, and got stronger.
- 02
But the group eating less every day built more leg muscle.
- 03
Even though both diets worked well for overall muscle and fat, eating less every day might help build more leg muscle during training.
Surprising findings
- Whole-body muscle gain was identical, but leg muscle size increased more with daily calorie restriction.Most people assume intermittent fasting protects muscle better during weight loss, but here it didn’t—even with protein matched and training controlled.
- Results differed by sex, but the study didn’t adjust for it in the main analysis.Sex can influence metabolism, muscle response, and fat loss, so ignoring this in analysis risks missing key differences—especially in a small study.
Practical takeaways
If you're trying to lose fat and gain muscle, focus on lifting weights and eating at least 1.4 g/kg of protein per day—whether you fast or eat less daily doesn’t matter much.
The study was short (12 weeks) and small (n=34), so long-term effects may differ.
medium confidenceIf building leg muscle is a priority, consider daily moderate calorie restriction instead of 5:2 fasting.
The difference was localized and measured via imaging—real-world impact on appearance or performance may be subtle.
medium confidenceDon’t expect faster muscle gain by fasting—your total weekly calories and protein intake are likely more important.
Results apply only to untrained individuals with overweight/obesity; trained athletes may respond differently.
high confidenceWhy this study matters
Same Fat Loss, Same Muscle Gain
Both the 5:2 fasting group and the daily calorie-cutting group lost 4.6% of their body weight and 24.1% of their fat, while gaining 3.7% lean body mass over 12 weeks. This happened because both groups lifted weights and ate at least 1.4 g/kg of protein per day.
It means you don’t have to suffer every day to see results—fasting just two days a week can work just as well for fat loss and muscle gain.
Daily Calorie Cut Builds Bigger Legs
Despite no difference in overall muscle gain, the continuous energy restriction group had significantly greater increases in mid-thigh muscle cross-sectional area measured by pQCT. This suggests localized muscle growth may be better with daily calorie control.
Even if the scale and body composition look the same, how you eat might affect where and how your muscles grow—especially in the legs.
Strength Gains Were Equal
Both groups improved their bench press and leg press 3RM and muscular endurance similarly, showing that neither diet hurt strength development when combined with resistance training and high protein.
You won’t get weaker by fasting—your strength progress depends more on lifting and protein than when you eat.
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
This study tested two diets—eating less every day or fasting two days a week—while doing strength training and eating enough protein.
Research results
Both groups gained 3.7% muscle, lost 4.6% weight and 24.1% fat, and got stronger. But the group eating less every day built more leg muscle.
What this means - more context
Even though both diets worked well for overall muscle and fat, eating less every day might help build more leg muscle during training.
The study aimed to compare the effects of 12 weeks of resistance training combined with either 5:2 intermittent fasting or continuous energy restriction on body composition, muscle size and quality, and strength in untrained individuals.
In untrained adults with overweight or obesity, both 5:2 intermittent fasting and continuous energy restriction, when combined with resistance training and protein intake ≥1.4 g/kg/day, led to similar improvements in lean body mass, fat mass, strength, and muscle quality over 12 weeks. However, continuous energy restriction resulted in greater increases in mid-thigh muscle cross-sectional area despite no difference in whole-body lean mass changes.
Methods Used
Thirty-four untrained adults (CERT = 17, IFT = 17) completed 12 weeks of resistance training (2 supervised, 1 unsupervised session/week) while following either 20% daily energy restriction or 5:2 intermittent fasting (~70% restriction 2 days/week), with both groups consuming ≥1.4 g/kg/day of protein. Outcomes included body composition, muscle size (pQCT, ultrasound), strength (3RM), and muscle quality.
Main Finding
Lean body mass increased by 3.7%, body weight decreased by 4.6%, and fat mass decreased by 24.1% with no significant differences between groups. Strength and muscle quality improved similarly in both groups. However, the continuous energy restriction group showed significantly greater increases in mid-thigh muscle cross-sectional area compared to the intermittent fasting group.
Confidence Level
Moderate to high; the study was a pre-registered randomized trial with objective outcome measures, but had a small sample size (n=34), short duration (12 weeks), and blinding status and randomization method were not specified.
Study Flags
Red Flags
- •Small sample size (n=34)
- •Blinding and randomization methods not specified
- •Results differed by sex, but not adjusted for in primary analysis
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
Whole-body muscle gain was identical, but leg muscle size increased more with daily calorie restriction.
Most people assume intermittent fasting protects muscle better during weight loss, but here it didn’t—even with protein matched and training controlled.
Practical Takeaways
If you're trying to lose fat and gain muscle, focus on lifting weights and eating at least 1.4 g/kg of protein per day—whether you fast or eat less daily doesn’t matter much.
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 552 / 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 watched two groups of people while they followed different diet plans along with strength training. It can show that both groups changed in similar ways, but it can't prove that the diets caused those changes because the groups weren't set up perfectly fairly.
Strengths
- Supervised training sessions ensuring protocol adherence
- Use of objective measures (DXA, pQCT, ultrasound)
- Controlled protein intake (~1.4 g/kg/day)
Weaknesses
- Randomization via coin toss without allocation concealment
- No mention of blinding of participants or assessors
- Small sample size underpowered for subgroup and local muscle differences
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
This study tested two diets—eating less every day or fasting two days a week—while doing strength training and eating enough protein.
Research results
Both groups gained 3.7% muscle, lost 4.6% weight and 24.1% fat, and got stronger. But the group eating less every day built more leg muscle.
What this means - more context
Even though both diets worked well for overall muscle and fat, eating less every day might help build more leg muscle during training.
The study aimed to compare the effects of 12 weeks of resistance training combined with either 5:2 intermittent fasting or continuous energy restriction on body composition, muscle size and quality, and strength in untrained individuals.
In untrained adults with overweight or obesity, both 5:2 intermittent fasting and continuous energy restriction, when combined with resistance training and protein intake ≥1.4 g/kg/day, led to similar improvements in lean body mass, fat mass, strength, and muscle quality over 12 weeks. However, continuous energy restriction resulted in greater increases in mid-thigh muscle cross-sectional area despite no difference in whole-body lean mass changes.
Methods Used
Thirty-four untrained adults (CERT = 17, IFT = 17) completed 12 weeks of resistance training (2 supervised, 1 unsupervised session/week) while following either 20% daily energy restriction or 5:2 intermittent fasting (~70% restriction 2 days/week), with both groups consuming ≥1.4 g/kg/day of protein. Outcomes included body composition, muscle size (pQCT, ultrasound), strength (3RM), and muscle quality.
Main Finding
Lean body mass increased by 3.7%, body weight decreased by 4.6%, and fat mass decreased by 24.1% with no significant differences between groups. Strength and muscle quality improved similarly in both groups. However, the continuous energy restriction group showed significantly greater increases in mid-thigh muscle cross-sectional area compared to the intermittent fasting group.
Confidence Level
Moderate to high; the study was a pre-registered randomized trial with objective outcome measures, but had a small sample size (n=34), short duration (12 weeks), and blinding status and randomization method were not specified.
Study Flags
Red Flags
- •Small sample size (n=34)
- •Blinding and randomization methods not specified
- •Results differed by sex, but not adjusted for in primary analysis
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
Whole-body muscle gain was identical, but leg muscle size increased more with daily calorie restriction.
Most people assume intermittent fasting protects muscle better during weight loss, but here it didn’t—even with protein matched and training controlled.
Practical Takeaways
If you're trying to lose fat and gain muscle, focus on lifting weights and eating at least 1.4 g/kg of protein per day—whether you fast or eat less daily doesn’t matter much.
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 552 / 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 watched two groups of people while they followed different diet plans along with strength training. It can show that both groups changed in similar ways, but it can't prove that the diets caused those changes because the groups weren't set up perfectly fairly.
Strengths
- Supervised training sessions ensuring protocol adherence
- Use of objective measures (DXA, pQCT, ultrasound)
- Controlled protein intake (~1.4 g/kg/day)
Weaknesses
- Randomization via coin toss without allocation concealment
- No mention of blinding of participants or assessors
- Small sample size underpowered for subgroup and local muscle differences
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study did some things well, like measuring muscles with special machines and guiding people through workouts. But it didn’t hide who was in which group, and people knew what diet they were on, which can affect results. That makes us less confident that the differences (or similarities) were truly because of the diets.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
35 / 100
- Randomizationrandomization unclear
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=34)+3.1/20
- Follow-up+10/10
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registration+15/15
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 552 / 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 cannot establish causation — the findings describe an association, not a cause. Randomization is described as 'coin toss' with no allocation concealment, making it unclear and not meeting RCT criteria per rules. Blinding status is unknown. Therefore, despite initial classification as RCT, it fails key methodological criteria and must be downgraded to cohort study.
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 Menno Henselmans cite this study, drawing 1 claim from it.
- Conflicting evidence
Evidence points in both directions — no clear conclusion yet.
Evidence