Could a daily vinegar drink help with constipation? A small trial offers a clue

By Tarun Sai LomteReviewed by Susha Cheriyedath, M.Sc.Aug 24 2026

A four-week randomized trial tested whether a simple vinegar drink could influence bowel habits and offered clues about how any effects might occur.

Study: Vinegar beverage consumption improves defecation status in constipation-prone healthy adults: a randomized, double-blind, placebo-controlled trial. Image Credit: Madeleine Steinbach / Shutterstock

In a recent study accepted for publication in the journal Scientific Reports, researchers in Japan investigated the effects of consuming a vinegar-based beverage on defecation in adults with mild constipation.

Constipation is characterized by incomplete, difficult, or infrequent defecation, and it is associated with increased chronic disease risk and reduced quality of life. Lifestyle modifications, especially dietary improvements, are the first-line treatment for most affected individuals. Meta-analytic evidence indicates that dietary fiber consumption improves defecation frequency. However, only 5% of the United States (US) population meets the recommended fiber intake levels.

The authors previously reported a positive association between consumption of a vinegar-based dish and defecation status, suggesting that vinegar intake could improve it. Nevertheless, their study had several limitations, including the lack of time-series data analysis, the inability to establish the optimal dose of vinegar or acetic acid (a potentially active constituent of vinegar), and potential confounding by unknown factors.

About the study

In the present study, researchers assessed the effects of consuming a vinegar beverage on defecation in healthy individuals with mild constipation. This randomized, double-blind, parallel-group, placebo-controlled trial was conducted in Japan during August–December 2024. The exploratory sample size was determined by feasibility rather than a formal statistical power calculation. Participants were healthy Japanese adults aged 20–69 years with a defecation frequency of three to five times in the week preceding screening (visit 1).

Pregnant or lactating individuals, those planning pregnancy, people with a history of (or undergoing treatment for) myocardial infarction, heart failure, or malignant tumor, and those taking medications, including herbal medicines, supplements, or foods with specific health uses/functional claims were excluded. The study also excluded people with a pacemaker or an implantable cardioverter-defibrillator and those receiving treatment for cerebrovascular disease, hypertension, diabetes, rheumatic disease, chronic kidney disease, cardiac arrhythmia, dyslipidemia, or other chronic diseases.

Participants were randomized to receive a vinegar beverage or a placebo beverage and were required to consume the assigned beverage with breakfast daily for four weeks. The vinegar beverage contained 750 mg of acetic acid in 200 ml of water, while the placebo beverage comprised 30 mg of citric acid in 200 ml of water. Both beverages were infused with apple flavoring and sucralose. Participants maintained their usual lifestyle and diet throughout the study.

Daily bowel diaries were maintained for a week preceding visit 1 and throughout the four-week intervention. Urinalyses, blood tests, medical interviews, fecal examinations, and body measurements were conducted at visits 1 and 2 (post-intervention). Fecal samples underwent DNA extraction and 16S rRNA gene sequencing. Alpha diversity of the fecal microbiota was estimated using the Shannon Index. The study's primary outcome was the frequency of defecation at week 4.

Exploratory secondary outcomes included stool volume and the number of defecation days during weeks 1–4; defecation frequency during weeks 1–3; alpha diversity before and after the intervention; the number of participants with improvements in stool characteristics; and sensation of defecation completeness during weeks 1–4. The team used a mixed-model repeated-measures design to assess the effects of the intervention on defecation status. Analyses were not adjusted for multiplicity.

Findings

The study included 44 participants, 22 per group. Most participants (64%) were female in both groups. Baseline age, body mass index (BMI), defecation status, and blood pressure did not significantly differ between groups. Mean adherence to the assigned beverage was 99.8% in the placebo group and 99.5% in the vinegar group, with individual adherence ranging from 92.9% to 100%. No adverse events related to the intervention were reported. The vinegar group had a significantly higher defecation frequency at week 4 than the placebo group. The adjusted between-group difference was approximately 1.2 additional bowel movements per week.

Defecation frequency and the number of defecation days tended to be greater in the vinegar group at week 1 than in the placebo group. The vinegar group also showed a tendency for increased stool volume at weeks 1 and 2. At week 1, the vinegar group showed a tendency toward a higher proportion of participants reporting an improved sensation of defecation completeness than the placebo group. Alpha diversity did not change significantly from before to after the intervention within either group, while an exploratory analysis also found no significant changes in beta diversity.

Bowel measures also appeared to improve gradually in both groups, leading the authors to speculate that habitual underhydration among some participants and the additional daily fluid intake could have contributed to the observed changes. However, the greater early improvements in the vinegar group could indicate a response specific to vinegar or acetic acid. The authors also proposed that vinegar might enhance the gastrocolic reflex and colonic motility rather than act primarily through changes in the gut microbiota, although this mechanism was not directly measured and remains speculative.

Conclusions

In summary, daily consumption of a vinegar beverage was associated with a significant increase in defecation frequency in healthy adults with mild constipation compared to placebo. Exploratory analyses suggested possible early improvements in stool volume, defecation frequency, and the number of defecation days as early as week 1, although these secondary analyses were not adjusted for multiple comparisons and differences were not consistent across all time points.

Further research is required in ethnically diverse populations, those with severe constipation, and to evaluate whether the effects sustain over time. The feasibility-based sample size, recruitment from online monitors, strict eligibility criteria, reliance on self-reported bowel diaries, use of a single vinegar dose, and lack of dietary monitoring during the intervention also limit the generalizability of the findings.

The study was funded by Mizkan Holdings Co., Ltd., and three of the authors were employees of the company.