Cohort studyindependent cross-checkfull text checked★ key study I-FAST-111 in-depth review
Safety of medically supervised multi-day fasting
Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects.
Overview
Wilhelmi de Toledo F et al.. PLoS One 2019 · PMID 30601864 · DOI 10.1371/journal.pone.0209353
In 1,422 clinic guests, supervised fasting with small amounts of juice and soup was mostly well tolerated; blood sugar fell to the low-normal range.
Does the study support the specific claim? Partly · Methodological quality: low
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Document safety and changes during Buchinger fasting.
- How was the study done?
One-year observational study, before-after measurements.
- How many people, animals or samples were studied?
1,422 adults at a German fasting clinic.
- What was actually found?
Weight and BP fell; glucose 4.7 mmol/L; ketones rose; adverse effects 0.7%; 2 hospital admissions.
- How large was the observed effect?
p<0.001 for weight, BP, glucose changes.
- What do the results mean in everyday life?
Short fasts under medical care with fluids and minimal calories are usually tolerated by selected healthy adults.
- What are the study's limitations?
No control group; clinic-run study; selected participants.
- What does it say about Elawady's specific claim?
Does not support 'zero inputs'; contradicts rising glucose as a normal fasting sign.
- Do the results apply to Germany and Europe?
German setting (Heilfasten); applicable to supervised fasting in Europe.
- What can explicitly not be concluded from this study?
Long-term health benefits; safety for excluded groups.
Scientific in-depth review
1. Full reference
- Authors
- Wilhelmi de Toledo F et al.
- Journal
- PLoS One
- Year
- 2019
- Identifier
- PMID 30601864 DOI 10.1371/journal.pone.0209353
- Verification
- verified – PubMed efetch 2026-10-26; Crossref update-to/updated-by check
- Retracted
- no
- Corrections
- none
- Extent checked
- full text
- Conflicts of interest and funding
First author is on the board of the clinic where the study was done; other authors employed by/consultants to the clinic (stated).
2. Research question
Is Buchinger periodic fasting of 4-21 days safe and what changes occur?
3. Study design and population
- Study design
- Cohort study – Prospective one-year observational cohort in a fasting clinic (pre-post)
- Population
Clinic guests aged 18-99 without contraindications (e.g. cachexia, anorexia nervosa, advanced kidney/liver/cerebrovascular insufficiency, dementia, pregnancy, lactation)
- Country
Germany (Überlingen)
- Period
not stated in abstract
- Sample size
1422
- Inclusion and exclusion criteria
Excluded predefined contraindications to Buchinger fasting; pregnancy and lactation excluded
4. Methods and endpoints
- Exposure / intervention
Buchinger fasting 200-250 kcal/day (juices, soups) plus fluids and a moderate lifestyle programme, 5-20 days, under medical supervision
- Comparator
Baseline values (no control group)
- Endpoints
Weight, BP, blood parameters, ketones, adverse effects, well-being
- Statistical methods
Mixed-effects linear models
5. Actual results
- Results
Weight, waist and blood pressure fell (p<0.001). Glucose decreased and 'stabilized at an average of 4.7 mmol/L'; ketone bodies increased. Adverse effects in 0.7% of subjects; 2 hospital admissions (one NSTEMI on day 9 in a 75-year-old man with known coronary disease); six cases of mild hyponatraemia (lowest 127 mmol/L). 84.4% of 404 with health complaints reported improvement.
- Absolute risks
not reported
- Authors' conclusion
Buchinger periodic fasting of 4-21 days is safe and well tolerated and improves well-being and risk factors.
6. Strengths
- Large sample
- Daily medical documentation
- Full text read
7. Weaknesses
- No control group
- Selected, paying, health-conscious clientele; contraindications excluded
- Strong conflict of interest
- Short follow-up; no hard outcomes
8. Risk of bias
- Orienting tool
- ROBINS-E
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- high
- Rationale
Uncontrolled pre-post design; conflicts of interest; selection.
9. Assessment of the statistical interpretation
Shows tolerability under supervision with some energy and ample fluid intake; it does not test 'zero inputs'. Glucose falls to low-normal in non-diabetic people. See stats/I-FAST-111_buchinger.py.
10. Relevance to the specific claim
Fair supporting evidence that supervised multi-day fasting with minimal energy and fluids is tolerated by selected healthy adults; contradicts 'zero inputs' (fluids and 200-250 kcal provided) and shows glucose falls, not rises, in non-diabetic fasting.
11. Independent contrary findings
12. Transferability to Germany and Europe
Universal biology; applies in Europe and Egypt.
13. Overall methodological judgement
Partly supports tolerability of supervised fasting; offers no support for 'infinite health'.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | low |
| Risk of bias | high |
| Precision of results | moderate |
| Directness | indirect |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
- Health equals the ability to avoid toxic inputs: zero inputs means infinite health; complete abstinence from all inputs (fasting) keeps the body in a state that does not become ill, and not eating for three or four days makes the body strong. – Studies with mixed or unclear results
- Rising blood glucose and acetone (ketones) during fasting are evidence that the liver is working properly, not a danger; high glucose plus acetone is not insulin deficiency. – Studies contradicting or limiting the claim