Combining Fasting and Fibre Interventions to Optimise Their Gut Microbiome-mediated Health Benefits

NCT07691736 | Not Yet Recruiting

• 1 other identifier: F-2026-010
• Study Type: interventional
• Target: 75
• Locations: 1 country
• Sites: 1

Brief Summary

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.

Conditions

Fasting; Dietary Fibre; Gut Microbiome; Metabolism Changes; Overweight , Obesity

Keywords

long-term fasting; fasting; continuous glucose monitoring; fibre supplementation; gut microbiome; metabolic health; resistant starch IV; metabolomics; ketosis; extracellular vesicles

Outcome Measures

Primary Outcomes (2)

• Abundance of butyrate-producing gut bacteria

  Change in the relative abundance of butyrate-producing gut bacteria assessed by metagenomic profiling of faecal samples.

  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).

  Baseline (T0) and end of the 10±4-day fasting period (T1)

Secondary Outcomes (7)

• Change in body weight

  Baseline (T0) and end of the 10±4-day fasting period (T1)

• Change in body mass index

  Baseline (T0) and end of the 10±4-day fasting period (T1)

• Change in waist circumference

  Baseline (T0) and end of the 10±4-day fasting period (T1)

• Change in HbA1c

  Baseline (T0) and end of the 10±4-day fasting period (T1)

• Change in HOMA index

  Baseline (T0) and end of the 10±4-day fasting period (T1)

Other Outcomes (55)

• Change in the abundance of butyrate-producing gut bacteria

  Baseline (T0), end of the 10±4-day fasting period (T1), and 1 month after fasting (T2)

• Change in body weight

  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

  Baseline (T0), daily during the 10±4-day fasting period and food reintroduction period, and 1 month after fasting (T2)

Study Arms (2)

Fibre Arm

ACTIVE COMPARATOR

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

Control Arm

PLACEBO COMPARATOR

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

Interventions

Fibre Arm DIETARY_SUPPLEMENT

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.

Fibre Arm

Control Arm DIETARY_SUPPLEMENT

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.

Control Arm

Eligibility Criteria

• Age: 18 Years - 65 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• Men and women
• Age: 18-65 years old
• Fasting for 10±4 days at the Buchinger Wilhelmi clinic in Überlingen
• BMI ≥ 25 kg/m²
• Signed informed consent

You may not qualify if:

• intake of antibiotics up to 2 months prior the study
• regular intake of pre-, post- and probiotics up to 2 months prior the study
• diagnosed Crohn's disease, Ulcerative colitis, IBD, coeliac disease
• medicated high blood pressure
• diagnosed diabetes mellitus type I
• medicated diabetes mellitus type II
• diagnosed kidney stone
• active malignant disease
• known substance addiction
• pregnancy or breastfeeding
• diagnosed with cachexia, anorexia nervosa, advanced kidney, liver or cerebrovascular insufficiency
• inability to sign the informed consent
• participation in another study

Sponsors & Collaborators

• Buchinger Wilhelmi Development & Holding GmbH: lead
• Buchinger Wilhelmi Clinic, 88662 Überlingen, Germany: collaborator
• King's College London, Faculty of Life Sciences & Medicine, Department of Nutritional Sciences, London, United Kingdom: collaborator
• Leiden University Medical Center, Department Leiden University Center for Infectious Diseases, 2333ZA, Leiden, Netherlands: collaborator
• TNO, Department Microbiology & Systems Biology, 2333 BE Leiden, Netherlands: collaborator
• Università degli Studi di Milano, Department of Pharmacological and Biomolecular Sciences Rodolfo Paoletti, Milan, Italy: collaborator
• Department of Cardio-Thoracic-Vascular Diseases, Foundation IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy: collaborator

Study Sites (1)

Buchinger Wilhelmi Development & Holding

Überlingen, Baden-Wurttemberg, 88662, Germany

Location

MeSH Terms

Conditions

Fasting; Overweight; Obesity; Ketosis

Condition Hierarchy (Ancestors)

Feeding Behavior; Behavior; Overnutrition; Nutrition Disorders; Nutritional and Metabolic Diseases; Body Weight; Signs and Symptoms; Pathological Conditions, Signs and Symptoms; Acidosis; Acid-Base Imbalance; Metabolic Diseases

Study Officials

• Andrea Siegler, Dr. med.

  Buchinger Wilhelmi Development & Holding

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Elena Katharina Stroppel

CONTACT

00497551807675; katharina.stroppel@buchinger-wilhelmi.com

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: DOUBLE
• Who Masked: PARTICIPANT, CARE PROVIDER
• Purpose: PREVENTION
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: June 24, 2026
• First Posted: July 9, 2026
• Study Start (Estimated): September 1, 2026
• Primary Completion (Estimated): February 28, 2027
• Study Completion (Estimated): March 1, 2027
• Last Updated: July 9, 2026

Record last verified: 2026-07

Locations

DE (1)