An interventional study of Fibre Arm and Control Arm in Fasting, Dietary Fibre and Gut Microbiome, sponsored by Buchinger Wilhelmi Development & Holding GmbH. Recruiting at 1 site in Germany. Open to participants aged 18 Years to 65 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-09-30.
Sponsored by Buchinger Wilhelmi Development & Holding GmbH · Not applicable, Interventional, and Prevention
This study builds on the knowledge that fasting provides metabolic health benefits and that prebiotic interventions can enhance the gut microbiome's metabolic output to likewise improve host health. Whether long-term fasting and dietary fibre interventions could be combined to achieve synergistic improvements in host metabolic health is however unknown. The goal is to provide a proof of concept in a human trial that supplementing 10±4 days fasting with dietary fibre synergistically improves metabolic outcomes via gut microbiome-mediated effects. To assess this, we aim to analyse gut microbiome changes, functional outputs, and key metabolic markers such as butyrate production, glycaemic control and ketosis.
The randomised controlled trial includes 75 participants and has two arms: one involving fasting with fibre supplementation (n = 50) and one involving fasting without fibre supplementation (n = 25). All participants will undergo a fasting period of 10±4 days according to the Buchinger Wilhelmi protocol, followed by a stepwise reintroduction of food of up to 4 days. As dietary fibre we will use maize-derived resistant starch type IV, selected based on its ability to stimulate beneficial gut microbes like Oscillibacter and corn starch as placebo. Two main visits will be conducted: before and at the end of the fasting period. During these visits, blood and stool samples will be collected, and questionnaires will be completed. Additionally, daily measurements of anthropometric parameters and well-being will be recorded. Stool samples will also be collected one month afterwards as a follow-up. Participants' metabolic health will be evaluated through various clinical parameters (e.g., body measurements, blood pressure, glycaemic control, ketones, well-being). Additionally, multi-omics data, including metagenomics and metabolomics, will provide insight into the composition of the microbiome, as well as its outputs and functions. Furthermore, the effects of fasting on extracellular vesicles in blood will be explored.
392 studies on the registry are indexed under Fasting; 63 are open to participants now.
This study's planned enrollment of 75 is above the median of 45 across 311 interventional studies indexed under Fasting.
Browse Fasting studies →Buchinger Wilhelmi Development & Holding GmbH is the lead sponsor of 5 studies on the registry; 2 are open to participants now.
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Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants (n=50) undergo a 10±4-day fasting period according to the Buchinger Wilhelmi fasting programme and receive maize-derived resistant starch type IV at a total dose of 20 g per day. The powder is blended into a carbohydrate-free electrolyte powder, divided into two equal daily doses, diluted in approximately 0.2 litres of water, and taken orally in the morning and at dinnertime throughout the fasting period. The fasting period is followed by a structured food reintroduction period according to the standard procedure of the Buchinger Wilhelmi Clinic. All other aspects of the intervention, including the fasting and nutritional protocol, clinical supervision, and study assessments, are identical to the control arm.
Dietary Supplement: Fibre Arm
Participants (n=25) undergo a 10±4-day fasting period according to the Buchinger Wilhelmi fasting programme and receive corn starch placebo at a total dose of 1.2 g per day. The powder is blended into a carbohydrate-free electrolyte powder, divided into two equal daily doses, diluted in approximately 0.2 litres of water, and taken orally in the morning and at dinnertime throughout the fasting period. The fasting period is followed by a structured food reintroduction period according to the standard procedure of the Buchinger Wilhelmi Clinic. All other aspects of the intervention, including the fasting and nutritional protocol, clinical supervision, and study assessments, are identical to the intervention arm.
Dietary Supplement: Control Arm
10±4 days of fasting according to the Buchinger Wilhelmi fasting protocol, followed by a structured food reintroduction period, combined with 20 g/day of maize-derived resistant starch type IV.
10±4 days of fasting according to the Buchinger Wilhelmi fasting protocol, followed by a structured food reintroduction period, combined with 1.2 g/day of corn starch placebo.
Abundance of butyrate-producing gut bacteria
Change in the relative abundance of butyrate-producing gut bacteria assessed by metagenomic profiling of faecal samples.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in fasting venous plasma glucose
Fasting venous plasma glucose concentration measured by clinical laboratory analysis (mmol/L).
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in body weight
Body weight (kg) measured as part of the clinical health assessment.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in body mass index
Body mass index calculated from measured body weight and height (kg/m²).
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in waist circumference
Waist circumference (cm) measured as part of the clinical health assessment.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in HbA1c
HbA1c (mmol/mol) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in HOMA index
HOMA index calculated from fasting plasma glucose and fasting insulin concentrations.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in fasting venous insulin
Fasting venous insulin concentration (pmol/L) measured by clinical laboratory analysis.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in glycaemic control assessed by continuous glucose monitoring
Glycaemic control assessed by blinded continuous glucose monitoring using the FreeStyle Libre 3 system, with glucose values recorded at 1-minute intervals (mmol/L).
Time frame: From Day 1 through Day 14
Change in the abundance of butyrate-producing gut bacteria
Exploratory assessment of the change in the abundance of butyrate-producing gut bacteria, derived from metagenomic profiling. Additional unscheduled samples may be collected during fasting if spontaneous bowel movements occur.
Time frame: Baseline (T0), end of the 10±4-day fasting period (T1), and 1 month after fasting (T2)
Change in body weight
Exploratory assessment of change in body weight (kg)
Time frame: Baseline (T0), daily during the 10±4-day fasting period and food reintroduction period, and 1 month after fasting (T2)
Change in body mass index
Exploratory assessment of change in body mass index (kg/m²).
Time frame: Baseline (T0), daily during the 10±4-day fasting period and food reintroduction period, and 1 month after fasting (T2)
Change in glycaemic control assessed by continuous glucose monitoring
Exploratory assessment of change in glycaemic control during the post-fasting follow-up period, assessed by open-label continuous glucose monitoring.
Time frame: From day 15 through day 28
Change in gut microbiome composition and functional output
Change in gut microbiome composition and functional output from baseline and the end of the fasting period to the one-month follow-up, assessed by metagenomics, metatranscriptomics, metabolomics, and short-chain fatty acid analysis. Additional unscheduled samples may be collected during fasting if spontaneous bowel movements occur
Time frame: Baseline, end of the 10±4-day fasting period, and 1 month after fasting
Height
Measurement of body height (cm)
Time frame: at baseline
Changes in resting blood pressure
Resting systolic blood pressure (mmHg) and resting diastolic blood pressure (mmHg) measured as part of the clinical health assessment and as self-measurement at follow-up.
Time frame: Baseline (T0), daily during the 10±4-day fasting period and food reintroduction period, and 1 month after fasting (T2)
Change in heart rate
Heart rate (beats/min) measured as part of the clinical health assessment and as self-measurement at follow-up.
Time frame: Baseline (T0), daily during the 10±4-day fasting period and food reintroduction period, and 1 month after fasting (T2)
Change in leucocyte count
Change in leucocyte count (10⁹/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in erythrocyte count
Change in erythrocyte count (10¹²/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in haemoglobin concentration
Change in haemoglobin concentration (g/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in haematocrit
Change in haematocrit levels (L/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in mean corpuscular volume (MCV)
Change in mean corpuscular volume (fL) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in mean corpuscular haemoglobin (MCH)
Change in mean corpuscular haemoglobin (pg) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in mean corpuscular haemoglobin concentration (MCHC)
Change in mean corpuscular haemoglobin concentration (g/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in thrombocyte count
Change in thrombocyte count (10⁹/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in lymphocyte count
Change in lymphocyte count (10⁹/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in international normalized ratio (INR)
Change in international normalized ratio (dimensionless) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in Quick value
Change in Quick value (%) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in partial thromboplastin time (PTT)
Change in partial thromboplastin time (seconds) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Changes in liver parameters
Liver-related parameters measured by clinical laboratory analysis of venous blood: aspartate aminotransferase (U/L), alanine aminotransferase (U/L), gamma-glutamyl transferase (U/L), and alkaline phosphatase (U/L).
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in uric acid
Change in uric acid levels (µmol/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in urea
Change in urea levels (mmol/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in creatinine
Change in creatinine levels (µmol/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in estimated glomerular filtration rate (eGFR)
Change in estimated glomerular filtration rate (mL/min/1.73 m²) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Changes in lipid parameters
Lipid parameters measured by clinical laboratory analysis of venous blood: total cholesterol (mmol/L), triglycerides (mmol/L), high-density lipoprotein cholesterol (mmol/L), low-density lipoprotein cholesterol (mmol/L), and non-high-density lipoprotein cholesterol (mmol/L).
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Changes in serum electrolyte concentrations
Electrolyte concentrations measured by clinical laboratory analysis of venous blood: sodium (mmol/L), potassium (mmol/L), calcium (mmol/L), and magnesium (mmol/L).
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in high-sensitivity C-reactive protein
High-sensitivity C-reactive protein concentration (mg/L) measured by clinical laboratory analysis of venous blood.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in extracellular vesicle size
Change in extracellular vesicle size (nm) derived from the analysis of venous blood samples.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in extracellular vesicle concentration
Change in extracellular vesicle concentration (particles/mL) derived from the analysis of venous blood samples.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Change in extracellular vesicle cargo profile
Change in extracellular vesicle cargo profile derived from the analysis of venous blood samples.
Time frame: Baseline (T0) and end of the 10±4-day fasting period (T1)
Changes in urinary acetoacetic acid
Acetoacetic acid measured in urine as a biomarker of ketosis.
Time frame: Baseline (T0) and daily during the 10±4-day fasting period and food reintroduction period
Change in WHO-5 well-being index
Change in WHO-5 (score: 0-100)
Time frame: Baseline (T0), end of the 10±4-day fasting period (T1), and 1 month after fasting (T2)
Changes in self-reported gut health and symptoms
Questionnaire-based assessment of gastrointestinal and systemic symptoms using a 0-to-10 numerical rating scale (where 0 = none/not full and 10 = very strong/very full). Symptoms assessed include hunger, bloating/fullness, flatulence, abdominal discomfort/pain, nausea, heartburn, acid regurgitation, cravings, fatigue, headache, and sleep disturbances.
Time frame: Baseline (T0), daily during the 10±4-day fasting period and food reintroduction period, end of the 10±4-day fasting period (T1), and 1 month after fasting (T2)
Change in self-reported physical activity
Change in physical activity level (hours/day) assessed by online questionnaires.
Time frame: Baseline (T0), daily during the 10±4-day fasting period and food reintroduction period (Day 1 through end of reintroduction), and 1 month after fasting (T2)
Change in self-reported physical activity
Change in physical activity level (VAS 0-10) assessed by online questionnaires.
Time frame: Baseline (T0), daily during the 10±4-day fasting period and food reintroduction period (Day 1 through end of reintroduction), and 1 month after fasting (T2)
Change in self-reported well-being
Change in self-reported physical and emotional well-being (VAS 0-10) as well as energy level (VAS 0-10) assessed by online questionnaires.
Time frame: Baseline (T0), daily during the 10±4-day fasting period and food reintroduction period (Day 1 through end of reintroduction), and 1 month after fasting (T2)
Occurrence of adverse effects
Number and characteristics of possible adverse effects assessed from participant reports and documentation by the study physician, including seriousness and possible relationship to the study intervention.
Time frame: Through study completion, an average of 7 weeks
Smoking behavior
status: never, former, current
Time frame: baseline
Confounding medical events and medication
Number of participants reporting concomitant medication use, supplement intake, or medical interventions (including antibiotics, prebiotics, probiotics, postbiotics, dietary supplements, hormonal therapies, surgeries, gastrointestinal endoscopies, or hospitalizations).
Time frame: Baseline (T0) and 1 month after fasting (T2)
Dietary patterns
Number of participants practicing specific dietary patterns (including omnivorous, flexitarian, pescetarian, vegetarian, vegan, or other specific diets like ketogenic).
Time frame: Baseline (T0) and 1 month after fasting (T2)
Change in intake of specific food categories
Questionnaire-based assessment of dietary fiber and fermented food intake (measured in portions per day or week) across specific food categories, including fruit, vegetables, bread and grain products, nuts and seeds, legumes, and fermented foods.
Time frame: Baseline (T0) and 1 month after fasting (T2)
Change in alcohol consumption
Questionnaire-based assessment of average weekly alcohol consumption (measured in standard glasses per week) across specific beverage types, including wine, beer, and spirits.
Time frame: Baseline (T0) and 1 month after fasting (T2)
Change in stool consistency
Change in usual stool consistency measured by the Bristol Stool Chart (Type 1 to Type 7; coded as an ordinal category).
Time frame: Baseline (T0) and 1 month after fasting (T2)
Change in bowel movement frequency
Change in typical bowel movement frequency categorized into four ordinal levels (from 1-2 times per week up to more than 3 times per day)
Time frame: Baseline (T0) and 1 month after fasting (T2)
Change in general gut health rating
Change in subjective general gut health rated on a 0-to-10 numerical rating scale (where 0 = very poor and 10 = excellent).
Time frame: Baseline (T0) and 1 month after fasting (T2)
Initial laxative methods
Number of participants utilizing specific laxative methods at the beginning of the fasting period (including Glauber's salt, Laxoberal, enemas, other laxatives, or no laxative use).
Time frame: End of the 10±4-day fasting period (T1)
Palatability of the dietary fiber supplement
Subjective taste rating of the dietary fiber supplement measured on a 7-point Likert scale (from "not at all" to "very good").
Time frame: End of the 10±4-day fasting period (T1)
Perceived change in digestion during fiber supplementation
Participant-reported change in digestion during the supplementation period, measured on a 7-point Likert scale (from "very negative" to "very positive").
Time frame: End of the 10±4-day fasting period (T1)
Tolerability of the dietary fiber supplement
Subjective tolerability rating of the dietary fiber supplement measured on a 7-point Likert scale (from "very poorly" to "very well").
Time frame: End of the 10±4-day fasting period (T1)
Intervention compliance
Compliance with the dietary fiber supplementation protocol, calculated as the percentage of prescribed doses successfully consumed (both morning and evening doses) during the fasting and food reintroduction periods, as verified by participant daily logs.
Time frame: Daily during the 10±4-day fasting period and food reintroduction period (Day 1 through end of reintroduction)
Utilization of optional supplements during fasting
Tracking the consumption of optional dietary additions permitted within the fasting protocol. This includes the number of participants choosing to consume midday juice, honey, or other additions (such as yogurt, Kousmine cream, oatmeal, or carrot juice).
Time frame: Daily during the 10±4-day fasting period (Day 1 through end of fasting (T1))
Daily bowel movement occurrence and induction method
Number of participants reporting a bowel movement each day, categorized by the method of clearance (none, spontaneous, induced by enema, induced by colon hydrotherapy, or induced by laxatives).
Time frame: Daily during the 10±4-day fasting period and food reintroduction period (Day 1 through end of reintroduction)
Daily spontaneous stool consistency
Daily assessment of stool consistency for participants with spontaneous bowel movements, scored using the Bristol Stool Chart (Type 1 to Type 7; analyzed as daily ordinal categories or mean scores).
Time frame: Daily during the 10±4-day fasting period and food reintroduction period (Day 1 through end of reintroduction)
Daily fluid intake
Daily self-reported volume of water or herbal tea consumed by participants, measured in liters (L).
Time frame: Daily during the 10±4-day fasting period and food reintroduction period
Plan to share: Undecided
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From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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