Meta-analysisindependent cross-checkfull text checked★ key study I-FAST-113 in-depth review
Different fasting methods compared
Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials.
Overview
Semnani-Azad Z et al.. BMJ 2025 · PMID 40533200 · DOI 10.1136/bmj-2024-082007
Across 99 trials, fasting diets led to weight loss similar to simply eating less every day; differences were small and short-term.
Does the study support the specific claim? Partly · Methodological quality: high
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Compare IF strategies with calorie restriction.
- How was the study done?
Network meta-analysis of 99 RCTs.
- How many people, animals or samples were studied?
6,582 adults.
- What was actually found?
ADF -1.29 kg vs CER in short trials; no long-term differences.
- How large was the observed effect?
MD -1.29 kg (-1.99 to -0.59).
- What do the results mean in everyday life?
Choose the eating pattern you can keep; fasting is not magic.
- What are the study's limitations?
Mostly short trials.
- What does it say about Elawady's specific claim?
Does not support one meal a day as 'the healthy way'; supports IF as one option.
- Do the results apply to Germany and Europe?
Applies; same physiology.
- What can explicitly not be concluded from this study?
Long-term disease outcomes.
Scientific in-depth review
1. Full reference
- Authors
- Semnani-Azad Z et al.
- Journal
- BMJ
- Year
- 2025
- Identifier
- PMID 40533200 DOI 10.1136/bmj-2024-082007
- Verification
- verified – PubMed efetch 2026-10-26; Crossref update-to/updated-by check
- Retracted
- no
- Corrections
Correction published: BMJ 2025;390:r1737 (PubMed ErratumIn; Crossref updated-by 'correction'); content of correction not affecting the main conclusions as far as can be judged from the record.
- Extent checked
- full text
- Conflicts of interest and funding
Funded mainly by agencies (NIDDK grant); some authors report food-industry-related honoraria (stated).
2. Research question
How do alternate-day fasting, time-restricted eating and whole-day fasting compare with continuous energy restriction and ad-libitum diets?
3. Study design and population
- Study design
- Meta-analysis – Systematic review and frequentist network meta-analysis with GRADE
- Population
Adults (720 healthy, 5862 with health conditions)
- Country
International
- Period
Search to 14 Nov 2024
- Sample size
99 RCTs, 6582 adults
- Inclusion and exclusion criteria
not stated in abstract
4. Methods and endpoints
- Exposure / intervention
ADF, TRE, whole-day fasting
- Comparator
Continuous energy restriction; ad-libitum diet
- Endpoints
Body weight (primary), anthropometry, glucose, lipids, BP, CRP, liver markers
- Statistical methods
Network MD with 95% CI; GRADE; funnel plots
5. Actual results
- Results
All IF and CER strategies reduced weight vs ad libitum. Vs CER only ADF showed benefit (MD -1.29 kg, 95% CI -1.99 to -0.59, moderate certainty); ADF vs TRE -1.69 kg (-2.49 to -0.88); ADF vs WDF -1.05 kg (-1.90 to -0.19). In trials >=24 weeks (n=17) diets only showed benefit vs ad libitum. No differences for HbA1c and HDL; TRE slightly raised total, LDL and non-HDL cholesterol vs WDF. Median follow-up 12 weeks (range 3-52).
- Absolute risks
not reported
- Authors' conclusion
Minor differences between some IF diets and CER; IF diets have similar benefits to CER for weight loss and cardiometabolic risk factors; longer trials needed.
6. Strengths
- Largest network of RCTs
- GRADE assessment
- Full text read
7. Weaknesses
- Short median follow-up
- Religious fasting excluded
- Heterogeneous populations
8. Risk of bias
- Orienting tool
- AMSTAR 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- low
- Rationale
Rigorous methods; limitations are in primary trials (short, dietary advice).
9. Assessment of the statistical interpretation
Differences of about 1-1.7 kg are small and limited to short trials; see stats/I-FAST-113_if_nma.py.
10. Relevance to the specific claim
Strongest evidence on whether fasting patterns are superior: they are about equivalent to ordinary calorie restriction.
11. Independent contrary findings
12. Transferability to Germany and Europe
Universal biology; applies in Europe and Egypt.
13. Overall methodological judgement
High-quality evidence: intermittent fasting is a valid option but not superior or uniquely healthy.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | low |
| Precision of results | high |
| Directness | direct |
| Reproducibility | replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | moderate |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
- Long daily intermittent fasting with one meal a day as the default eating pattern (and sometimes eating once every two days) is the healthy way to eat. – Studies with mixed or unclear results
- Fasting gives the liver and gut the chance to repair themselves and expel toxins; intermittent fasting is the only treatment for fatty liver and treats joint pain, autoimmune and allergy-like symptoms. – Studies contradicting or limiting the claim