Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects

PLoS One. 2019 Jan 2;14(1):e0209353. doi: 10.1371/journal.pone.0209353. eCollection 2019.


Only few studies document longer periods of fasting in large cohorts including non-obese participants. The aim of this study was to document prospectively the safety and any changes in basic health and well-being indicators during Buchinger periodic fasting within a specialised clinic. In a one-year observational study 1422 subjects participated in a fasting program consisting of fasting periods of between 4 and 21 days. Subjects were grouped in fasting period lengths of 5, 10, 15 and 20±2 days. The participants fasted according to the Buchinger guidelines with a daily caloric intake of 200-250 kcal accompanied by a moderate-intensity lifestyle program. Clinical parameters as well as adverse effects and well-being were documented daily. Blood examinations before and at the end of the fasting period complemented the pre-post analysis using mixed-effects linear models. Significant reductions in weight, abdominal circumference and blood pressure were observed in the whole group (each p<0.001). A beneficial modulating effect of fasting on blood lipids, glucoregulation and further general health-related blood parameters was shown. In all groups, fasting led to a decrease in blood glucose levels to low norm range and to an increase in ketone bodies levels (each p<0.001), documenting the metabolic switch. An increase in physical and emotional well-being (each p<0.001) and an absence of hunger feeling in 93.2% of the subjects supported the feasibility of prolonged fasting. Among the 404 subjects with pre-existing health-complaints, 341 (84.4%) reported an improvement. Adverse effects were reported in less than 1% of the participants. The results from 1422 subjects showed for the first time that Buchinger periodic fasting lasting from 4 to 21 days is safe and well tolerated. It led to enhancement of emotional and physical well-being and improvements in relevant cardiovascular and general risk factors, as well as subjective health complaints.

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Biomarkers / blood
  • Blood Cell Count
  • Blood Coagulation
  • Blood Glucose / metabolism
  • Blood Pressure
  • Cohort Studies
  • Electrolytes / blood
  • Fasting / adverse effects
  • Fasting / blood
  • Fasting / physiology*
  • Female
  • Health Promotion / methods*
  • Humans
  • Inflammation Mediators / blood
  • Ketone Bodies / urine
  • Kidney / physiology
  • Lipids / blood
  • Liver / enzymology
  • Male
  • Middle Aged
  • Prospective Studies
  • Safety
  • Time Factors
  • Waist Circumference
  • Weight Loss
  • Young Adult


  • Biomarkers
  • Blood Glucose
  • Electrolytes
  • Inflammation Mediators
  • Ketone Bodies
  • Lipids

Grants and funding

The study was financed by Amplius GmbH, Überlingen, Germany. This company has the task to develop a research department for the Buchinger Wilhelmi Clinics Überlingen and Marbella who are the funders. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding received for this study.