Study analysis · Clinical nutrition · 2025
16:8 fasting helped young men lose 2.8 kg in 6 weeks—but they also lost 1.4 kg of lean mass and saw no improvement in blood markers.
In healthy young men, eating only during an 8-hour window for 6 weeks led to weight and fat loss, but also muscle loss, and did not improve blood sugar, cholesterol, or fat burning during exercise.
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 one group of guys a new eating schedule and another group kept eating normally, then measured what changed. Because they randomly assigned who got which plan, we can say the eating schedule probably caused the fat loss—not just that people who ate this way happened to be thinner.
What’s the bottom line?
In a 6-week trial, young men who ate only during an 8-hour window lost body weight and fat and burned more fat at rest than men who ate normally. But they also lost some lean mass. Blood sugar, cholesterol, and exercise fat burning did not improve.
How strong is this study?
It’s a pretty good study because they randomly split people into groups and compared them fairly. But we don’t know if the researchers or participants knew who was in which group, which could have influenced results. So it’s solid, but not perfect.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
60 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=33)+3.0/20
- 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 560 / 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 abstract explicitly states that participants were randomized into TRE and control groups, allowing for causal inference despite unknown blinding status. Randomization and control group are clearly described, meeting criteria for Level 1b.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding information were disclosed in the study text.
The study lacks any declaration of funding, conflicts of interest, or author affiliations with industry. While the results appear methodologically sound, the absence of transparency in funding and COI disclosures limits the ability to fully assess potential bias.
Key takeaways
- 01
Absolute changes over 6 weeks: TRE vs control: body mass -2.8 kg vs +0.7 kg; fat mass -1.4 kg vs +0.4 kg; body fat -1.7 percentage points vs +0.4; lean mass -1.4 kg vs +0.3 kg; visceral fat -39.7 g vs +46.4 g.
- 02
Resting fat oxidation +0.33 vs -0.37 mg/kg FFM/min; resting RER -0.02 vs +0.02.
- 03
No significant blood marker or exercise fat oxidation changes.
- 04
These are absolute differences, not relative risks.
- 05
The average TRE participant lost about 2.8 kg body mass and 1.4 kg fat mass over 6 weeks, but also about 1.4 kg lean mass.
- 06
The resting fat-burning increase was small; the study did not test long-term health outcomes or disease risk.
- 07
Absolute risk of disease was not reported.
Practical takeaways
If you try 16:8 TRE for fat loss, monitor lean mass (e.g., via DEXA or bioimpedance) and consider resistance training and adequate protein to protect muscle.
The study did not test strategies to prevent lean mass loss, and this is not an explicit recommendation from the abstract. Full paper was not available.
low confidenceDon't expect 6 weeks of 16:8 to improve fasting glucose, insulin, or cholesterol if you're a healthy young man—this study found no significant changes.
Only 33 healthy young males were studied for 6 weeks; longer or different populations may show different results. Abstract only.
low confidenceIf your goal is better fat burning during exercise, 16:8 may not help—this study found no change in exercise substrate oxidation.
Exercise was cycling at 40% VO2max; other intensities or modalities may differ. No full text.
low confidenceWhy this study matters
Weight and fat loss—but also lean mass loss
Over 6 weeks, the 16:8 TRE group had absolute changes of -2.8 kg body mass, -1.4 kg fat mass, -1.7% body fat, and -39.7 g visceral fat, while controls gained +0.7 kg body mass, +0.4 kg fat mass, +0.4% body fat, and +46.4 g visceral fat. However, the TRE group also lost -1.4 kg lean mass versus +0.3 kg in controls. All between-group differences were significant (p<0.05).
Most people focus on scale weight and fat loss, but losing lean mass can hurt metabolism, strength, and long-term health—especially if you're not lifting weights or eating enough protein.
Resting metabolism shifted toward fat burning
Resting fat oxidation increased by +0.33 mg/kg FFM/min in TRE versus -0.37 in controls (p=0.007), while resting RER decreased by -0.02 versus +0.02 (p=0.016) and carbohydrate oxidation decreased by -0.39 versus +0.45 mg/kg FFM/min (p=0.037). Lower RER means the body is using more fat and less carbohydrate at rest.
This supports the popular idea that fasting can make your body better at burning fat while you're just sitting around—but it doesn't necessarily translate to better exercise performance or health markers.
No improvements in blood glucose, insulin, or cholesterol
Fasting blood glucose, insulin, triglycerides, total cholesterol, and HDL cholesterol did not significantly change in either group (p>0.05). This was despite significant body composition improvements in the TRE group.
Many people assume weight loss automatically improves metabolic health, but in healthy young men over just 6 weeks, blood markers stayed the same.
Exercise fat burning didn't improve
Fat oxidation during moderate-intensity cycling at 40% VO2max did not significantly change over time in either group (p>0.05). This contrasts with the increase in resting fat oxidation.
Athletes and fitness enthusiasts often use fasted training to boost fat burning during exercise, but this study found no such benefit after 6 weeks of 16:8.
Small, short, and only in young healthy men
The trial included only 33 healthy young males (age 27.5 ± 6 years, VO2max 43.9 ± 6.6 mL/kg/min) and lasted just 6 weeks. The abstract does not report blinding or confidence intervals, and full methodology is unavailable.
Results may not apply to women, older adults, people with obesity or diabetes, or anyone looking for long-term outcomes.
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
In a 6-week trial, young men who ate only during an 8-hour window lost body weight and fat and burned more fat at rest than men who ate normally. But they also lost some lean mass. Blood sugar, cholesterol, and exercise fat burning did not improve.
Research results
Absolute changes over 6 weeks: TRE vs control: body mass -2.8 kg vs +0.7 kg; fat mass -1.4 kg vs +0.4 kg; body fat -1.7 percentage points vs +0.4; lean mass -1.4 kg vs +0.3 kg; visceral fat -39.7 g vs +46.4 g. Resting fat oxidation +0.33 vs -0.37 mg/kg FFM/min; resting RER -0.02 vs +0.02. No significant blood marker or exercise fat oxidation changes.
What this means - more context
These are absolute differences, not relative risks. The average TRE participant lost about 2.8 kg body mass and 1.4 kg fat mass over 6 weeks, but also about 1.4 kg lean mass. The resting fat-burning increase was small; the study did not test long-term health outcomes or disease risk. Absolute risk of disease was not reported.
To determine the effect of a 6-week 16:8 time-restricted eating (TRE) program on resting and exercise substrate oxidation, body composition, and blood markers related to metabolic health in healthy young males.
In 33 healthy young males, 6 weeks of 16:8 TRE vs control produced significant absolute reductions in body mass (-2.8 kg vs +0.7 kg), fat mass (-1.4 kg vs +0.4 kg), percent body fat (-1.7% vs +0.4%), lean mass (-1.4 kg vs +0.3 kg), and visceral adipose tissue (-39.7 g vs +46.4 g). Resting RER decreased (-0.02 vs +0.02; p=0.016), resting fat oxidation increased (0.33 vs -0.37 mg/kg FFM/min; p=0.007), and carbohydrate oxidation decreased (-0.39 vs +0.45 mg/kg FFM/min; p=0.037). Exercise substrate oxidation and fasting glucose, insulin, triglycerides, total cholesterol, and HDL did not significantly change (p>0.05).
Methods Used
Thirty-three healthy young males (age 27.5 ± 6 years, body mass 76.5 ± 8.4 kg, VO2max 43.9 ± 6.6 mL/kg/min) were assigned to TRE (n=16) or control (n=17) with efforts to match baseline characteristics. TRE followed a 16:8 program for 6 weeks; controls maintained existing dietary habits. Body composition, blood glucose, insulin, blood lipids, resting substrate oxidation, and fat oxidation during cycling at 40% VO2max were assessed before and after. Data analyzed with intention-to-treat and per-protocol approaches.
Main Finding
Compared with control, 6-week 16:8 TRE produced significant absolute changes: body mass -2.8 kg vs +0.7 kg; fat mass -1.4 kg vs +0.4 kg; percent body fat -1.7% vs +0.4%; lean mass -1.4 kg vs +0.3 kg; visceral adipose tissue -39.7 g vs +46.4 g. Resting RER decreased -0.02 vs +0.02 (p=0.016); resting fat oxidation increased 0.33 vs -0.37 mg/kg FFM/min (p=0.007); carbohydrate oxidation decreased -0.39 vs +0.45 mg/kg FFM/min (p=0.037). No significant changes in exercise substrate oxidation or fasting glucose, insulin, triglycerides, total cholesterol, or HDL (p>0.05).
Confidence Level
Limited - based on abstract only, full methodology not available. RCT design and pre-registration noted, but small sample, no blinding or confidence intervals reported in abstract.
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Small sample (n=33) and short 6-week duration
- •Blinding and confidence intervals not reported in abstract
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.
Practical Takeaways
If you try 16:8 TRE for fat loss, monitor lean mass (e.g., via DEXA or bioimpedance) and consider resistance training and adequate protein to protect muscle.
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 560 / 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 one group of guys a new eating schedule and another group kept eating normally, then measured what changed. Because they randomly assigned who got which plan, we can say the eating schedule probably caused the fat loss—not just that people who ate this way happened to be thinner.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Explicit randomization into intervention and control groups
- Use of intention-to-treat and per-protocol analyses
- Baseline characteristics matched between groups
Weaknesses
- Blinding status unknown - potential for performance or detection bias
- Full methodology not available - based on abstract only
- Small sample size (n=33)
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
In a 6-week trial, young men who ate only during an 8-hour window lost body weight and fat and burned more fat at rest than men who ate normally. But they also lost some lean mass. Blood sugar, cholesterol, and exercise fat burning did not improve.
Research results
Absolute changes over 6 weeks: TRE vs control: body mass -2.8 kg vs +0.7 kg; fat mass -1.4 kg vs +0.4 kg; body fat -1.7 percentage points vs +0.4; lean mass -1.4 kg vs +0.3 kg; visceral fat -39.7 g vs +46.4 g. Resting fat oxidation +0.33 vs -0.37 mg/kg FFM/min; resting RER -0.02 vs +0.02. No significant blood marker or exercise fat oxidation changes.
What this means - more context
These are absolute differences, not relative risks. The average TRE participant lost about 2.8 kg body mass and 1.4 kg fat mass over 6 weeks, but also about 1.4 kg lean mass. The resting fat-burning increase was small; the study did not test long-term health outcomes or disease risk. Absolute risk of disease was not reported.
To determine the effect of a 6-week 16:8 time-restricted eating (TRE) program on resting and exercise substrate oxidation, body composition, and blood markers related to metabolic health in healthy young males.
In 33 healthy young males, 6 weeks of 16:8 TRE vs control produced significant absolute reductions in body mass (-2.8 kg vs +0.7 kg), fat mass (-1.4 kg vs +0.4 kg), percent body fat (-1.7% vs +0.4%), lean mass (-1.4 kg vs +0.3 kg), and visceral adipose tissue (-39.7 g vs +46.4 g). Resting RER decreased (-0.02 vs +0.02; p=0.016), resting fat oxidation increased (0.33 vs -0.37 mg/kg FFM/min; p=0.007), and carbohydrate oxidation decreased (-0.39 vs +0.45 mg/kg FFM/min; p=0.037). Exercise substrate oxidation and fasting glucose, insulin, triglycerides, total cholesterol, and HDL did not significantly change (p>0.05).
Methods Used
Thirty-three healthy young males (age 27.5 ± 6 years, body mass 76.5 ± 8.4 kg, VO2max 43.9 ± 6.6 mL/kg/min) were assigned to TRE (n=16) or control (n=17) with efforts to match baseline characteristics. TRE followed a 16:8 program for 6 weeks; controls maintained existing dietary habits. Body composition, blood glucose, insulin, blood lipids, resting substrate oxidation, and fat oxidation during cycling at 40% VO2max were assessed before and after. Data analyzed with intention-to-treat and per-protocol approaches.
Main Finding
Compared with control, 6-week 16:8 TRE produced significant absolute changes: body mass -2.8 kg vs +0.7 kg; fat mass -1.4 kg vs +0.4 kg; percent body fat -1.7% vs +0.4%; lean mass -1.4 kg vs +0.3 kg; visceral adipose tissue -39.7 g vs +46.4 g. Resting RER decreased -0.02 vs +0.02 (p=0.016); resting fat oxidation increased 0.33 vs -0.37 mg/kg FFM/min (p=0.007); carbohydrate oxidation decreased -0.39 vs +0.45 mg/kg FFM/min (p=0.037). No significant changes in exercise substrate oxidation or fasting glucose, insulin, triglycerides, total cholesterol, or HDL (p>0.05).
Confidence Level
Limited - based on abstract only, full methodology not available. RCT design and pre-registration noted, but small sample, no blinding or confidence intervals reported in abstract.
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Small sample (n=33) and short 6-week duration
- •Blinding and confidence intervals not reported in abstract
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.
Practical Takeaways
If you try 16:8 TRE for fat loss, monitor lean mass (e.g., via DEXA or bioimpedance) and consider resistance training and adequate protein to protect muscle.
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 560 / 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 one group of guys a new eating schedule and another group kept eating normally, then measured what changed. Because they randomly assigned who got which plan, we can say the eating schedule probably caused the fat loss—not just that people who ate this way happened to be thinner.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Explicit randomization into intervention and control groups
- Use of intention-to-treat and per-protocol analyses
- Baseline characteristics matched between groups
Weaknesses
- Blinding status unknown - potential for performance or detection bias
- Full methodology not available - based on abstract only
- Small sample size (n=33)
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
It’s a pretty good study because they randomly split people into groups and compared them fairly. But we don’t know if the researchers or participants knew who was in which group, which could have influenced results. So it’s solid, but not perfect.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
60 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=33)+3.0/20
- 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 560 / 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 abstract explicitly states that participants were randomized into TRE and control groups, allowing for causal inference despite unknown blinding status. Randomization and control group are clearly described, meeting criteria for Level 1b.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding information were disclosed in the study text.
The study lacks any declaration of funding, conflicts of interest, or author affiliations with industry. While the results appear methodologically sound, the absence of transparency in funding and COI disclosures limits the ability to fully 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.
2 videos from 2 different creators cite this study, drawing 2 claims from it.
- Very strong evidence
Randomized or controlled trials support this claim, alongside consistent supporting evidence.
Evidence
- Good evidence
Good evidence supports this claim, with little to contradict it.
Evidence
Authored by
6 researchersIf this is your work, this is how we attribute it on Fit Body Science. Muhammed M. Atakan is listed as the lead author.