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.

Waist circumference (cm) measured as part of the clinical health assessment.

HbA1c (mmol/mol) measured by clinical laboratory analysis of venous blood.

HOMA index calculated from fasting plasma glucose and fasting insulin concentrations.

Fasting venous insulin concentration (pmol/L) measured by clinical laboratory analysis.

Glycaemic control assessed by blinded continuous glucose monitoring using the FreeStyle Libre 3 system, with glucose values recorded at 1-minute intervals (mmol/L).

Exploratory assessment of change in body weight (kg)

Exploratory assessment of change in body mass index (kg/m²).

Exploratory assessment of change in glycaemic control during the post-fasting follow-up period, assessed by open-label continuous glucose monitoring.

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

Measurement of body height (cm)

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.

Heart rate (beats/min) measured as part of the clinical health assessment and as self-measurement at follow-up.

Change in leucocyte count (10⁹/L) measured by clinical laboratory analysis of venous blood.

Change in erythrocyte count (10¹²/L) measured by clinical laboratory analysis of venous blood.

Change in haemoglobin concentration (g/L) measured by clinical laboratory analysis of venous blood.

Change in haematocrit levels (L/L) measured by clinical laboratory analysis of venous blood.

Change in mean corpuscular volume (fL) measured by clinical laboratory analysis of venous blood.

Change in mean corpuscular haemoglobin (pg) measured by clinical laboratory analysis of venous blood.

Change in mean corpuscular haemoglobin concentration (g/L) measured by clinical laboratory analysis of venous blood.

Change in thrombocyte count (10⁹/L) measured by clinical laboratory analysis of venous blood.

Change in lymphocyte count (10⁹/L) measured by clinical laboratory analysis of venous blood.

Change in international normalized ratio (dimensionless) measured by clinical laboratory analysis of venous blood.

Change in Quick value (%) measured by clinical laboratory analysis of venous blood.

Change in partial thromboplastin time (seconds) measured by clinical laboratory analysis of venous blood.

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).

Change in uric acid levels (µmol/L) measured by clinical laboratory analysis of venous blood.

Change in urea levels (mmol/L) measured by clinical laboratory analysis of venous blood.

Change in creatinine levels (µmol/L) measured by clinical laboratory analysis of venous blood.

Change in estimated glomerular filtration rate (mL/min/1.73 m²) measured by clinical laboratory analysis of venous blood.

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).

Electrolyte concentrations measured by clinical laboratory analysis of venous blood: sodium (mmol/L), potassium (mmol/L), calcium (mmol/L), and magnesium (mmol/L).

High-sensitivity C-reactive protein concentration (mg/L) measured by clinical laboratory analysis of venous blood.

Change in extracellular vesicle size (nm) derived from the analysis of venous blood samples.

Change in extracellular vesicle concentration (particles/mL) derived from the analysis of venous blood samples.

Change in extracellular vesicle cargo profile derived from the analysis of venous blood samples.

Acetoacetic acid measured in urine as a biomarker of ketosis.

Change in WHO-5 (score: 0-100)

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.

Change in physical activity level (hours/day) assessed by online questionnaires.

Change in physical activity level (VAS 0-10) assessed by online questionnaires.

Change in self-reported physical and emotional well-being (VAS 0-10) as well as energy level (VAS 0-10) assessed by online questionnaires.

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.

status: never, former, current

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).

Number of participants practicing specific dietary patterns (including omnivorous, flexitarian, pescetarian, vegetarian, vegan, or other specific diets like ketogenic).

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.

Questionnaire-based assessment of average weekly alcohol consumption (measured in standard glasses per week) across specific beverage types, including wine, beer, and spirits.

Change in usual stool consistency measured by the Bristol Stool Chart (Type 1 to Type 7; coded as an ordinal category).

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)

Change in subjective general gut health rated on a 0-to-10 numerical rating scale (where 0 = very poor and 10 = excellent).

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).

Subjective taste rating of the dietary fiber supplement measured on a 7-point Likert scale (from "not at all" to "very good").

Participant-reported change in digestion during the supplementation period, measured on a 7-point Likert scale (from "very negative" to "very positive").

Subjective tolerability rating of the dietary fiber supplement measured on a 7-point Likert scale (from "very poorly" to "very well").

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.

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).

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).

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).

Daily self-reported volume of water or herbal tea consumed by participants, measured in liters (L).