Fermented Foods and Bone Health: Investigating the Gut-Bone Axis in Premenopausal Vegan Women (FERMBONE)

Plant-based diets are increasingly adopted for health and environmental reasons, but they are associated with lower bone mineral density, higher fracture risk, and elevated bone turnover markers, particularly in women. These effects are partly explained by lower intakes of calcium and zinc, and higher concentrations of phytates and oxalates, substances that inhibit mineral absorption from plant foods. Evidence-based dietary strategies to support bone health in vegan populations beyond supplementation remain limited.

Fermented plant-based foods may help address this gap through two complementary mechanisms: first, by delivering live microorganisms that beneficially modulate gut microbiota and promote the production of short-chain fatty acids, which support mineral absorption and reduce bone resorption, and second, by reducing antinutritional factors such as phytates during microbial fermentation, thereby improving mineral bioavailability.

This study investigates whether the daily consumption of fermented plant-based foods, specifically lacto-fermented vegetables, calcium-fortified plant-based yogurt alternatives with live cultures, and Rhizopus-fermented tempeh, reduces bone resorption and improves calcium metabolism in premenopausal women following a vegan diet. Participants will follow each dietary condition (fermented or matched non-fermented control foods) for 12 weeks in randomized order, separated by an 8-week washout period. Blood, urine, and stool samples are collected at each study visit to assess bone turnover markers, gut microbiota composition, short-chain fatty acid production, inflammatory markers, and a range of metabolic and nutritional parameters.

Study Overview

• Status: Not yet recruiting
• Conditions: Bone; Bone Health
• Intervention / Treatment: Other: Fermented Plant-Based Foods; Other: Non-Fermented Plant-Based Foods

Detailed Description

Vegan diets are associated with lower bone mineral density and elevated fracture risk, partly due to reduced intake of calcium and zinc and higher concentrations of phytates and oxalates, which inhibit intestinal mineral absorption. Emerging evidence suggests that the gut microbiota plays a key regulatory role in bone metabolism through the gut-bone axis, primarily via production of short-chain fatty acids (SCFAs), which enhance mineral absorption, modulate immune responses, and suppress osteoclastogenesis. Fermented plant-based foods may beneficially modulate this axis by delivering live microorganisms and by reducing antinutritional factors through microbial phytase activity, thereby improving mineral bioavailability.

FERMBONE is a randomized, controlled, open-label, two-period crossover trial conducted at two sites: ETH Zürich (Switzerland) and Královské Vinohrady University Hospital (Prague, Czech Republic). Fifty premenopausal vegan women are enrolled (25 per site).

Study Design and phases:

After a screening visit, participants attend a baseline visit (week 0) to assess baseline characteristics and enter a 4-week run-in period during which fermented plant-based foods are excluded from the diet to standardize gut microbiota baseline. Participants are then randomized to one of two sequences: fermented foods in Phase I (weeks 4-16) followed by control foods in Phase II (weeks 24-36), or the reverse. The two 12-week intervention phases are separated by an 8-week washout period (weeks 16-24) during which the same dietary restrictions as in the run-in apply.

Intervention:

The fermented food intervention comprises three categories consumed daily: calcium-fortified fermented plant-based yogurt alternatives with live cultures, lacto-fermented vegetables including sauerkraut and kimchi, and Rhizopus-fermented tempeh, for a minimum combined total of 14 portions per week across at least two categories daily. The matched control condition consists of non-fermented plant-based equivalents: calcium-fortified plant-based milk, fresh raw vegetables, and cooked non-fermented legumes, matched at the group level for portion size, energy, protein, and calcium content. All study foods are commercially available and provided to participants.

Assessments:

Study visits are conducted at baseline and at the beginning and end of each intervention phase (weeks 0, 4, 16, 24, 36). At each visit, fasting venous blood samples, morning spot urine, and stool samples are obtained. Anthropometric measurements, blood pressure, standardized questionnaires, and a weighed 3-day dietary record are completed at each visit. A single DXA scan is performed during the run-in period to assess the baseline bone density.

Biological analyses:

Bone turnover markers (CTX, P1NP, ALP) and endocrine regulators (PTH, 25(OH)D) are measured from fasting serum. Further, urinary calcium, phosphate, and creatinine are measured. Gut microbiota composition is assessed by whole-genome metagenomic sequencing and fecal SCFAs are quantified by targeted metabolomics. Inflammatory and intestinal integrity markers (CRP, AGP, IL-6, iFABP), fecal pH and calprotectin, hemoglobin, and DNA methylation-based epigenetic aging markers are analyzed along with iron status markers (ferritin, soluble transferrin receptor) and metabolic parameters (glucose, insulin, lipid profile).

• Study Type: Interventional
• Enrollment (Estimated): 50
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Isabelle Herter-Aeberli, PhD; Phone Number: +41 44 632 74 81; Email: isabelle.herter@hest.ethz.ch

Study Locations

• Czechia
  • Prague
    • Prague, Prague, Czechia, 100 00
      • Third Faculty of Medicine
      • Contact: Jan Gojda, Prof. Dr.; Phone Number: +420267163031; Email: jan.gojda@lf3.cuni.cz
• Switzerland
  • Canton of Zurich
    • Zurich, Canton of Zurich, Switzerland, 8092
      • Swiss Federal Institute of Technology
      • Contact: Isabelle Herter-Aeberli, PhD; Phone Number: +41 44 632 74 81; Email: isabelle.herter@hest.ethz.ch
      • Principal Investigator: Isabelle Herter-Aeberli, PhD

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Female, aged 28-43years.
• Body mass index (BMI) between 18.5 and 24.9 kg/m².
• Premenopausal, with regular menstrual cycles. *
• Adherence to a vegan diet for ≥1 year, confirmed by questionnaire.
• Willingness to consume both fermented and non-fermented plant-based study foods.
• Ability to comply with all study procedures, including run-in, washout, sample collection, and clinic visits.

• Signed written and oral informed consent.

  • Regular menstrual cycles are defined as spontaneous menstrual bleeding occurring every 21-35 days, with cycle-to-cycle variability not exceeding 7-9 days over the prior three months, and bleeding duration of 3-8 days, in the absence of hormonal contraception or endocrine disorders.

Exclusion Criteria:

• Chronic diseases or conditions affecting bone metabolism (e.g., osteoporosis, thyroid disorders, chronic kidney and liver disease, menstrual cycles disorders affecting bone health, conditions associated with malabsorption).
• History of diagnosed eating disorders.
• Chronic inflammatory or gastrointestinal diseases (e.g., IBD, celiac disease).
• Recent antibiotic use (within 3 months prior to screening).
• Use of Vitamin D supplements exceeding 2000 IU/day.
• Abnormal DXA results (T-score ≤ -2.5).
• Pregnancy, intention to become pregnant, or lactation during the course of the study
• Use of hormonal contraceptives.
• Use of medications influencing bone metabolism (e.g., glucocorticoids, antiresorptives).
• BMI <18.5 or >24.9 kg/m².
• Known or suspected non-compliance, drug or alcohol abuse
• Inability to follow the procedures of the studies, e.g. due to language problems, psychological disorders, dementia, etc. of the participant or anticipated prolonged absence (e.g. extended travel).
• Participation in another clinical study within the last 3 months.
• Known allergy or intolerance to study foods.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Prevention
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Fermented Plant-Based Foods; Participants consume three categories of fermented plant-based foods daily for 12 weeks: lacto-fermented vegetables, fermented plant-based yogurt alternatives with live cultures and calcium fortification, and Rhizopus-fermented tempeh, with a minimum combined weekly target of 14 portions.	Other: Fermented Plant-Based Foods; Daily consumption of three categories of fermented plant-based foods for 12 weeks: lacto-fermented vegetables, fermented plant-based yogurt alternatives with live cultures and calcium fortification, and Rhizopus-fermented tempeh. Minimum combined weekly target: 14 portions.
Active Comparator: Non-Fermented Control Foods; Participants consume non-fermented plant-based equivalents matched for portion size, energy, protein, and calcium content for 12 weeks: non-fermented calcium-fortified plant-based milk, fresh raw vegetables, and cooked non-fermented legumes.	Other: Non-Fermented Plant-Based Foods; Daily consumption of non-fermented plant-based equivalents for 12 weeks, matched to the intervention arm for portion size, energy, protein, and calcium content: non-fermented calcium-fortified plant-based milk, fresh raw vegetables, and cooked non-fermented legumes.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Fasting serum CTX concentration	Within-subject difference in fasting serum C-terminal telopeptide of type I collagen (CTX) concentration between the end of the fermented food intervention phase and the end of the matched control phase, measured by electrochemiluminescence immunoassay (ECLIA).	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Fasting serum P1NP concentration	Serum procollagen type 1 N-terminal propeptide (P1NP), a marker of bone formation reflecting osteoblast activity, measured by ECLIA.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Fasting serum alkaline phosphatase (ALP) concentration	Serum alkaline phosphatase (ALP), a non-specific marker of bone formation reflecting osteoblast activity, measured by standard clinical chemistry methods.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Fasting serum parathyroid hormone (PTH) concentration	Parathyroid hormone (PTH), an endocrine regulator of calcium homeostasis, measured by immunoassay at the University Hospital Zurich from fasting serum (ng/l).	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Fasting serum 25-hydroxyvitamin D (25(OH)D) concentration	Serum 25-hydroxyvitamin D (25(OH)D), a marker of vitamin D status, measured by immunoassay at the University Hospital Zurich (nmol/l).	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Urinary calcium-to-creatinine ratio (CCR)	Calcium-to-creatinine ratio from morning spot urine samples, reflecting renal calcium handling and dietary calcium absorption.	Baseline (Week 0); Week 4, Week 16, Week 24, Week 36
Urinary phosphate-to-creatinine ratio	Phosphate-to-creatinine ratio from morning spot urine samples, reflecting renal phosphate handling.	Baseline (Week 0); Week 4, Week 16, Week 24, Week 36

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Gut microbiota composition and diversity	Whole-genome metagenomic sequencing of stool sample using Illumina NextSeq 500 (150 bp paired-end). Taxonomic profiling with MetaPhlAn 4; metabolic pathway abundance with HUMAnN 3.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Fecal short-chain fatty acid (SCFA) concentrations	Targeted metabolomics of fecal SCFA concentrations from ethanol-preserved stool samples.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Fasting plasma glucose	Fasting plasma glucose is measured using standard clinical chemistry methods.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Hemoglobin concentration	Hemoglobin measured from fasting whole blood samples using standard clinical chemistry methods.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Iron status	Serum ferritin and soluble transferrin receptor (sTfR) measured by standard methods from fasting serum or plasma.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Epigenetic ageing	DNA methylation-based epigenetic ageing markers: Biological age estimated from DNA methylation in EDTA whole blood using established epigenetic clock algorithms. Expressed as estimated biological age (years) and epigenetic age acceleration (difference between biological and chronological age).	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Serum C-reactive protein (CRP) concentration	CRP, a marker of systemic inflammation, measured by multiplex immunoassay from fasting serum samples.	Baseline (Week 0); Week 4, Week 16, Week 24, Week 36
Dietary quality score (VEGANScreener)	Diet quality assessed using the VEGANScreener, a 29-item screener for vegans (Kronsteiner-Gicevic et al., Nutrients 2024). The tool includes 25 frequency-based food group questions (9 response options: never to ≥3 times/day) and 4 binary (yes/no) nutrient/supplement questions. The VEGANScreener identifies areas of dietary adequacy and inadequacy at the item level. Unit of Measure: Frequency category per item	Baseline
General health and lifestyle survey (study-specific baseline questionnaire)	A study-specific structured questionnaire administered at baseline to characterize the study population. It collects data on sociodemographic background (e.g. age, education, occupation), lifestyle factors (e.g. smoking, alcohol use, sun exposure), dietary supplement use, and habitual food patterns. Data are used for descriptive analyses and as potential covariates in statistical models. No composite score is generated; individual item responses are recorded in the electronic case report form.	Baseline
International Physical Activity Questionnaire iPAQ (short form)	Physical activity is assessed using a study-specific short form of the International Physical Activity Questionnaire. The questionnaire captures the frequency and duration of walking, moderate-intensity activity, and vigorous-intensity activity over the past 7 days. Higher values indicate greater physical activity. Data are used for descriptive analyses and as potential covariates in statistical models. No composite score is generated.	Baseline (week 0), week 4, week 16, week 24, week 36
Bone mineral density	Bone mineral density (BMD) at the lumbar spine, femoral neck, and total hip will be assessed by dual-energy X-ray absorptiometry (DXA).	Baseline
Body weight	Weight will be measured in kg	Baseline (week 0), week 4, week 16, week 24, week 36
Height	Height will be measured in m	Baseline (week 0), week 4, week 16, week 24, week 36
Waist circumference	Waist circumference will be measured in cm	Baseline (week 0), week 4, week 16, week 24, week 36
Hip circumference	Hip circumference will be measured in cm	Baseline (week 0), week 4, week 16, week 24, week 36
Blood pressure	Systolic and diastolic blood pressure will be measured	Baseline (week 0), week 4, week 16, week 24, week 36
Heart rate	Heart rate will be measured	Baseline (week 0), week 4, week 16, week 24, week 36
Vegan dietary habits and adherence (study-specific dietary habits questionnaire)	A study-specific structured questionnaire assessing adherence to and characteristics of the vegan diet, including duration of vegan diet (years), use of dietary supplements, and habitual food consumption patterns. Administered at each study visit to monitor changes in dietary behavior across phases. Data are used for descriptive analyses and as covariates in statistical models; no composite score is generated. Participant-reported response (categorical and continuous items)	Baseline (week 0), week 4, week 16, week 24, week 36
Menstrual cycle characteristics (standardized study-specific self-report tracking form)	Menstrual cycle characteristics are assessed using a standardized study-specific self-report tracking form. Menstrual cycle phase and regularity assessed via a standardized self-report tracking form completed by participants at home throughout the study. The form records cycle length (days), first day of menstrual bleeding, bleeding duration (days), and associated symptoms at each cycle. Data are used as a covariate to control for hormonal variation at the time of blood sampling. No composite score is generated.	Baseline (Week 0) through Week 36 (up to 36 weeks)
Intervention acceptability (study-specific acceptability questionnaire)	Acceptability of the fermented food intervention and matched control products assessed using a study-specific questionnaire administered at the end of each 12-week intervention phase. 10 questionnaire evaluates palatability, ease of preparation, convenience, and willingness to continue consuming the study foods using Likert-type response options (1 = strongly disagree to 5 = strongly agree) and 3 open-end questions to assess the preference overall. Higher scores indicate greater acceptability. Results are used to characterize the feasibility of the dietary intervention.	Administered twice after completion of the fermented food intervention phase and the control phase (week 16 and week 36)
Intervention adherence	Adherence to the fermented food intervention and control phase assessed using a study-specific weekly compliance tracking sheet. Participants self-report the number of portions consumed from each of the three study food categories (fermented or control) per week. Adherence is defined as meeting the weekly portion targets (minimum 14 total portions/week across at least 2 of 3 food categories). The proportion of compliant weeks is calculated per participant per phase.	Week 4 through Week 16 (Phase I) and Week 24 through Week 36 (Phase II)
Serum alpha-1-acid glycoprotein (AGP) concentration	AGP, an acute-phase protein and marker of systemic inflammation, measured by multiplex immunoassay from fasting serum samples.	Baseline (Week 0); Week 4, Week 16, Week 24, Week 36
Plasma interleukin-6 (IL-6) concentration	IL-6, a pro-inflammatory cytokine, measured by ELISA from fasting plasma samples.	Baseline (Week 0); Week 4, Week 16, Week 24, Week 36
Plasma intestinal fatty acid-binding protein (iFABP) concentration	iFABP, a marker of intestinal epithelial integrity, measured by ELISA from fasting plasma samples.	Baseline (Week 0); Week 4, Week 16, Week 24, Week 36
Fecal pH	Fecal pH measured on a continuous scale (range 0-14; lower values indicate a more acidic colonic environment, which is generally associated with favorable microbiota composition) from unfixed stool samples	Baseline (Week 0); Week 4, Week 16, Week 24, Week 36
Fecal calprotectin concentration	Fecal calprotectin, a marker of intestinal inflammation, measured by ELISA from unfixed stool samples.	Baseline (Week 0); Week 4, Week 16, Week 24, Week 36
General health status follow-up (study-specific follow-up questionnaire)	General health status and potential protocol deviations assessed using a study-specific structured follow-up questionnaire administered at each study visit (Weeks 4, 16, 24, and 36). The questionnaire captures changes e.g. in medication use, recent illnesses, antibiotic use, stress levels, dietary deviations, physical activity changes, and sun exposure since the last visit. Data are used to identify and document protocol deviations and potential confounders, no composite score is generated. Participant-reported response (categorical items; presence or absence of health status changes).	Week 4, Week 16, Week 24, Week 36
Dietary intake	Dietary intake will be assessed at three timepoints using a 3-day weighed food record (two non-consecutive weekdays and one weekend day), analyzed in a dietary assessment software. Reported outcomes include total macronutrient and micronutrient intake. Data are used to characterize dietary exposure during each study phase and as covariates in statistical analyses.	Pre-baseline (Week -3 to 0), mid-Phase I (Week 11-12), mid-Phase II (Week 31-32)
Fasting serum insulin	Fasting serum insulin is measured using standard clinical chemistry methods.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Fasting plasma cholesterol	Fasting plasma total cholesterol is measured using standard clinical chemistry methods.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Fasting plasma HDL	Fasting plasma high-density lipoprotein (HDL) cholesterol is measured using standard clinical chemistry methods.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Fasting plasma LDL	Fasting plasma low-density lipoprotein (LDL) cholesterol is measured using standard clinical chemistry methods.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)
Fasting plasma triglycerides	Fasting plasma triglycerides are measured using standard clinical chemistry methods.	Baseline (Week 0), at the beginning and end of each 12-week intervention phase (Weeks 4, 16, 24, and 36)

Collaborators and Investigators

• Sponsor: Isabelle Herter-Aeberli
• Collaborators: Charles University, Czech Republic; Swiss National Science Foundation; Philhuman Foundation; Czech Science Foundation

Study record dates

Study Major Dates

• Study Start (Estimated): May 31, 2026
• Primary Completion (Estimated): May 31, 2027
• Study Completion (Estimated): May 31, 2027

Study Registration Dates

• First Submitted: May 22, 2026
• First Submitted That Met QC Criteria: June 10, 2026
• First Posted (Actual): June 12, 2026

Study Record Updates

• Last Update Posted (Actual): June 12, 2026
• Last Update Submitted That Met QC Criteria: June 10, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: Gut microbiota; Bone health; Plant-based diet; Premenopausal women; Vegan diet; Fermented foods; Gut-bone axis
• Other Study ID Numbers: 2026-00984

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED
• IPD Plan Description: Can be shared upon reasonable request and in compliance with ethical regulations.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No