Fermented foods such as kefir, sauerkraut, kimchi, and yogurt are often promoted for gut health. For fermented foods for constipation, the evidence is more limited than the marketing suggests, and much of it was not designed to answer a constipation question.
A 2025 systematic review and meta-analysis of 25 studies (4,328 healthy adults) found that fermented food consumption was associated with differences in bowel movement frequency, stool consistency, intestinal transit time, and some constipation-related outcomes. However, the studies varied widely, the certainty of evidence was mostly low, and the participants did not have diagnosed gastrointestinal disorders, so the findings do not show that fermented foods treat chronic constipation [1].
Quick answer: Fermented foods may help some people with constipation, but the evidence is early. Kefir has some of the most direct data, from one small study of 20 adults with no control group [2] [3]. Sauerkraut and kimchi have been tested mainly in people with irritable bowel syndrome (IBS), not constipation alone [4] [5]. None of them replaces fiber, fluids, or medical care when symptoms persist.
What Counts as a Fermented Food?
An expert panel convened by the International Scientific Association for Probiotics and Prebiotics (ISAPP) defined fermented foods as foods and drinks made through intentional microbial growth and the enzymatic conversion of their ingredients [6]. Yogurt, kefir, sauerkraut, kimchi, miso, tempeh, and kombucha all fit.
A fermented food is not automatically a probiotic food, because some products are heat treated after fermentation and no longer contain live microbes [6]. A probiotic is a live microorganism that gives a health benefit when taken in adequate amounts [2].
A 2019 review (which did not cover yogurt or cheese) found that kefir, sauerkraut, natto, and sourdough bread were the only common fermented foods tested in at least one randomized trial for gut effects, and it called the clinical evidence very limited [7]. It predates the newer studies discussed here, so it is an earlier snapshot rather than the current evidence base.
How Fermented Foods Might Affect Bowel Movements
Proposed routes include changes in the gut microbiota and its metabolites, and interaction with the immune system and the enteric nervous system, a key regulator of gut motility [2]. Fermentation can also produce compounds such as short-chain fatty acids and lactic acid, which have been proposed as possible contributors to effects on the gut environment and motility [8].
These ideas come mostly from laboratory and supplement studies, and it is still an open question whether typical food portions deliver enough of the right microbes to matter. See our guide to the gut microbiome and constipation.
What the Human Studies Actually Show
| Food | Best available human evidence | Who was studied | Main limitation |
|---|---|---|---|
| Fermented foods overall (2025 meta-analysis) | Intake was associated with differences in bowel movement frequency, stool consistency, and intestinal transit time [1] | 25 studies, 4,328 healthy adults (19 RCTs in the meta-analysis) | Healthy adults rather than adults diagnosed with chronic constipation; mostly fermented dairy; high heterogeneity; certainty mostly low |
| Kefir | In one uncontrolled study, participants drank about 500 mL a day for 4 weeks, and stool frequency, stool consistency, and bowel satisfaction were better and laxative use was lower than at baseline. Colonic transit was faster in the slow-transit subgroup [2] [3] | 20 adults with chronic constipation (10 with normal transit, 10 with slow transit) | No control group; kefir was specially prepared for the study; not yet confirmed in randomized trials |
| Yogurt and fermented milk | One randomized trial found more frequent stools with 220 mL a day of pasteurized yogurt than with pasteurized milk [9]. A fermented milk containing Bifidobacterium animalis DN-173 010 has also been tested against a heat-treated yogurt in constipation-predominant IBS [10] | 120 adults with chronic constipation enrolled, 118 completed (yogurt trial); 274 adults with constipation-predominant IBS (fermented milk trial) | The yogurt trial was rated high risk of bias [2] |
| Sauerkraut | Both pasteurized and unpasteurized sauerkraut were followed by lower IBS symptom scores over 6 weeks [4] | 34 adults with IBS | Small and underpowered; IBS, not constipation alone; no group without sauerkraut |
| Kimchi | 210 g a day for 12 weeks: IBS symptoms improved in all three kimchi groups, while dietary fiber intake also increased during the intervention [5] | 90 adults with IBS, 30 in each of three kimchi groups | Every group ate kimchi (one standard, one with added dead Lactobacillus plantarum nF1, one “functional”), so there was no kimchi-free comparison; IBS, not constipation alone |
| High fermented food diet | A 10-week diet increased gut microbiota diversity and lowered markers of inflammation [11] | Healthy adults | Not a constipation trial |
| Kombucha, miso, tempeh | We did not identify controlled human trials specifically testing these foods for constipation | Not applicable | No evidence base to say they help |
Most of these trials are small, short, or both, and several had no control group, so they cannot separate the effect of the food from placebo response. IBS can include constipation but is not the same condition as chronic constipation.
Fermented Foods vs. Probiotic Supplements
Probiotic supplements have been studied in a much larger number of controlled trials than fermented foods, partly because supplements can provide defined strains and doses. A 2022 meta-analysis of 30 randomized trials found that 57% of adults with chronic constipation responded to probiotics compared with 44% on control, and that probiotics increased stool frequency overall [12].
Bifidobacterium lactis was associated with a significant increase in stool frequency in subgroup analysis, while mixtures of probiotics and Lactobacillus casei Shirota did not [12].
The evidence does not support recommending a specific probiotic strain for everyone with constipation, and the 2025 British Dietetic Association guideline likewise described probiotic effects as species-, strain-, and outcome-specific [13].
Foods rarely list strains or doses, so supplement findings cannot be assumed to apply to them, and no trial has compared the two. See our guides to the best probiotic strains for constipation and bloating, whether probiotics help constipation, and prebiotic vs probiotic for gut health.
Notes on Kefir, Yogurt, Sauerkraut, and Kimchi
- Kefir. Without a control group, the 2014 pilot cannot exclude placebo response, straining did not change significantly [3], and a 2025 review noted that kefir has only been tested in uncontrolled studies for constipation [2]. It is not a proven treatment. Choose plain versions, because flavored kefir often carries added sugar.
- Yogurt. The evidence is mixed. The 120-person trial of pasteurized yogurt was rated high risk of bias [2], and the 274-person fermented milk trial tested one specific strain, Bifidobacterium animalis DN-173 010, in IBS with constipation [10]. See our guide to Greek yogurt and constipation.
- Sauerkraut. Symptom scores improved with both pasteurized and unpasteurized products, so the findings do not show that live bacteria were necessary for the benefit. Other components of cabbage, such as fiber, may play a role, but that is a hypothesis, not a conclusion [4].
- Kimchi. The authors described the study as double-blind and placebo-controlled, but all three groups received a kimchi product, so it did not include a true no-kimchi dietary control [5]. At 210 g a day, the portion was also much larger than a small garnish.
How to Add Fermented Foods Step by Step
No trial has established an ideal dose, so the following is a cautious starting approach rather than a protocol.
- Start small. Try a spoonful or two of sauerkraut or kimchi with a meal, or a small glass of plain kefir, and increase gradually. Some people notice gas or bloating at first.
- Give it a few weeks and track it. Note how often you go and your stool type using the Bristol Stool Form Scale, where types 1 and 2 point to constipation. There is no established time point at which fermented foods should be expected to work. Three to four weeks is a reasonable personal tracking period, not a clinically established treatment duration.
- Read the label. If you want a product that still contains live microbes, check for live and active cultures and refrigerated storage, but live cultures do not by themselves show a constipation benefit. Also look for minimal added sugar.
- Keep the basics. Fermented foods should complement, not replace, the broader dietary and lifestyle measures used to manage constipation, such as an appropriate fiber intake, adequate fluid intake when needed, and regular physical activity. Our guides to the best fruits for chronic constipation, a plant-based diet for constipation relief, and dehydration and constipation explain how.
Psyllium has substantially stronger clinical evidence for chronic constipation than the fermented foods discussed here [2]. If you are considering a fiber supplement, read psyllium husk vs wheat bran for constipation first.
Who Should Be Careful With Fermented Foods
Fermented foods vary in their microbial content, sodium, acidity, sugar, and food-safety considerations, so tolerance and suitability can differ by product and person. A few groups should take extra care.
- People with weakened immune systems or serious illness. Serious infections have been reported rarely with some probiotic products, particularly in premature infants and in people who are seriously ill or immunocompromised [14]. That evidence does not establish the same risk for ordinary fermented foods, but people in these groups should ask their healthcare professional before adding them regularly.
- People taking MAOI antidepressants. Mayo Clinic lists pickled or fermented foods such as sauerkraut and kimchi among foods that can be high in tyramine, and notes that kombucha and kefir may also have higher levels. The amount varies considerably by product and storage, so follow the restrictions given by your prescriber or pharmacist [15].
- People who limit sodium. Sauerkraut and kimchi can be salty. The American Heart Association advises most adults to stay under 2,300 mg of sodium a day, with an ideal limit of 1,500 mg for most adults [16].
- People with a milk allergy or lactose intolerance. Regular kefir and yogurt are dairy products.
- People with IBS or a sensitive gut. New fermented foods may cause gas or bloating, so go slowly, and stop and talk to a healthcare professional if symptoms get worse.
- People who are pregnant, breastfeeding, or feeding young children. Follow age-appropriate food-safety guidance, and ask a healthcare professional if you are using fermented foods specifically to manage constipation.
When Constipation Needs a Doctor
A diet experiment is reasonable for mild, occasional constipation, but not for warning signs. The National Institute of Diabetes and Digestive and Kidney Diseases advises seeing a doctor right away for rectal bleeding, blood in the stool, constant abdominal pain, an inability to pass gas, vomiting, fever, lower back pain, or unintended weight loss [17]. Mayo Clinic also lists symptoms lasting longer than three weeks as a reason to get checked [18].
To understand when constipation is considered chronic, read What Is Chronic Constipation?. If diet alone is not enough, our guides to the best OTC laxatives for constipation and the best natural laxatives cover options to discuss with a clinician.
Fermented Food Staples and Tools Worth Considering
As an Amazon Associate, we earn from qualifying purchases. This does not change which products we mention.
Products mentioned here are convenience options, not evidence-based treatments, and none of them is a treatment for constipation. Prices and stock change often, so check the current listing, and refrigerate perishable items as the label directs.
Kefir at home. The Cultures for Health Kefir Starter Culture is a freeze-dried powder starter, and its listing says it can culture milk, water, or juice. Homemade kefir may differ from the kefir used in the 2014 study, and plain milk kefir is the closest match if dairy suits you.
Raw sauerkraut. Wildbrine Organic Green Sauerkraut (18 oz) is described on its listing as live, raw, and never pasteurized. The sauerkraut trial found benefits with both pasteurized and unpasteurized versions, so raw is not required. Raw does not automatically mean better for everyone; if you are in a higher-risk group for foodborne infection, choose fermented foods according to your healthcare professional’s advice.
Kimchi. Wildbrine Kimchi (18 oz) is listed as raw, vegan, and fish free.
A simple fermenting setup. The Masontops Fermentation Jar Starter Set includes a wide-mouth Mason jar, an airlock lid, and a glass weight, according to its listing. Follow a tested recipe from a trusted food safety source, and use clean equipment.
A fiber partner. NOW Organic Psyllium Husk Powder (12 oz) is a fiber option with substantially stronger clinical evidence for chronic constipation than the fermented foods discussed here. Follow the label directions and increase gradually. Take it with adequate fluid according to the product label and your clinician’s advice, and check with your clinician if you take regular medication.
Frequently Asked Questions
Do fermented foods help with constipation?
They might help some people, but the evidence is not strong yet. Kefir has some of the most direct data, from one small study without a control group. Sauerkraut and kimchi have been studied mainly in people with irritable bowel syndrome. If you try them, track your symptoms over several weeks, and keep fiber and fluids in place.
How long do fermented foods take to work?
There is no established time at which fermented foods should be expected to relieve constipation. The studies discussed here lasted four to twelve weeks, but that does not prove that benefits take that long to appear. If you choose to try them, track your symptoms over several weeks rather than expecting a same-day laxative effect.
Should I eat fermented foods or take a probiotic supplement for constipation?
No trial has compared the two. Supplements list specific strains and doses, and certain Bifidobacterium lactis strains have shown benefit in a meta-analysis. Fermented foods rarely list strains or doses, so supplement results cannot be assumed to apply to them. Ask a healthcare professional before choosing a supplement.
The Bottom Line
Fermented foods for constipation are an interesting idea with early, imperfect evidence: a small uncontrolled study for kefir, small IBS trials for sauerkraut and kimchi, mixed results for yogurt, and no constipation trials for kombucha, miso, or tempeh. A 2025 meta-analysis in healthy adults found differences in bowel habits, but with mostly low-certainty evidence and without testing people who have chronic constipation.
Fermented foods are tolerated by many people, but tolerance and safety can vary by product and person. They should be considered an optional dietary addition, not a primary treatment for persistent constipation.
If you try them, start small and track your symptoms over several weeks rather than expecting a quick laxative effect, while keeping up your fiber, fluids, and daily movement. Our guide to simple morning habits to relieve constipation is a good place to start. If you notice warning signs or nothing improves, see a healthcare professional.
References
- Mukherjee A, Farsi DN, Garcia-Gutierrez E, et al. Impact of fermented foods consumption on gastrointestinal wellbeing in healthy adults: a systematic review and meta-analysis. Front Nutr. 2025;12:1668889. doi:10.3389/fnut.2025.1668889. https://doi.org/10.3389/fnut.2025.1668889
- Dimidi E. Dietary management of chronic constipation: a review of evidence-based strategies and clinical guidelines. Proc Nutr Soc. 2025;84(4):398-410. doi:10.1017/S0029665125100694. https://doi.org/10.1017/S0029665125100694
- Turan I, Dedeli O, Bor S, Ilter T. Effects of a kefir supplement on symptoms, colonic transit, and bowel satisfaction score in patients with chronic constipation: a pilot study. Turk J Gastroenterol. 2014;25(6):650-6. doi:10.5152/tjg.2014.6990. https://doi.org/10.5152/tjg.2014.6990
- Nielsen ES, Garnas E, Jensen KJ, Hansen LH, Olsen PS, Ritz C, et al. Lacto-fermented sauerkraut improves symptoms in IBS patients independent of product pasteurisation: a pilot study. Food Funct. 2018;9(10):5323-35. PMID: 30256365. https://pubmed.ncbi.nlm.nih.gov/30256365/
- Kim HY, Park ES, Choi YS, Park SJ, Kim JH, Chang HK, et al. Kimchi improves irritable bowel syndrome: results of a randomized, double-blind placebo-controlled study. Food Nutr Res. 2022;66. doi:10.29219/fnr.v66.8268. https://doi.org/10.29219/fnr.v66.8268
- Marco ML, Sanders ME, Ganzle M, Arrieta MC, Cotter PD, De Vuyst L, et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nat Rev Gastroenterol Hepatol. 2021;18(3):196-208. doi:10.1038/s41575-020-00390-5. https://doi.org/10.1038/s41575-020-00390-5
- Dimidi E, Cox SR, Rossi M, Whelan K. Fermented foods: definitions and characteristics, impact on the gut microbiota and effects on gastrointestinal health and disease. Nutrients. 2019;11(8):1806. doi:10.3390/nu11081806. https://doi.org/10.3390/nu11081806
- Dimidi E, Christodoulides S, Scott SM, Whelan K. Mechanisms of action of probiotics and the gastrointestinal microbiota on gut motility and constipation. Adv Nutr. 2017;8(3):484-94. PMID: 28507013. https://pubmed.ncbi.nlm.nih.gov/28507013/
- Liu ZM, Xu ZY, Han M, Guo BH. Efficacy of pasteurised yoghurt in improving chronic constipation: a randomised, double-blind, placebo-controlled trial. Int Dairy J. 2015;40:1-5. https://www.sciencedirect.com/science/article/abs/pii/S095869461400171X
- Guyonnet D, Chassany O, Ducrotte P, et al. Effect of a fermented milk containing Bifidobacterium animalis DN-173 010 on the health-related quality of life and symptoms in irritable bowel syndrome in adults in primary care: a multicentre, randomized, double-blind, controlled trial. Aliment Pharmacol Ther. 2007;26(3):475-86. PMID: 17635382. https://pubmed.ncbi.nlm.nih.gov/17635382/
- Wastyk HC, Fragiadakis GK, Perelman D, Dahan D, Merrill BD, Yu FB, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137-53.e14. doi:10.1016/j.cell.2021.06.019. https://doi.org/10.1016/j.cell.2021.06.019
- van der Schoot A, Helander C, Whelan K, Dimidi E. Probiotics and synbiotics in chronic constipation in adults: a systematic review and meta-analysis of randomized controlled trials. Clin Nutr. 2022;41(12):2759-77. doi:10.1016/j.clnu.2022.10.015. https://doi.org/10.1016/j.clnu.2022.10.015
- Dimidi E, van der Schoot A, Barrett K, et al. British Dietetic Association guidelines for the dietary management of chronic constipation in adults. J Hum Nutr Diet. 2025;38(5):e70133. doi:10.1111/jhn.70133. https://doi.org/10.1111/jhn.70133
- National Center for Complementary and Integrative Health. Probiotics: usefulness and safety. https://www.nccih.nih.gov/health/probiotics-usefulness-and-safety
- Mayo Clinic. MAOIs and diet: is it necessary to restrict tyramine? https://www.mayoclinic.org/diseases-conditions/depression/expert-answers/maois/faq-20058035
- American Heart Association. Salt (sodium) can be sneaky infographic. https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/sodium/sodium-can-be-sneaky-infographic
- National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms and causes of constipation. https://www.niddk.nih.gov/health-information/digestive-diseases/constipation/symptoms-causes
- Mayo Clinic. Constipation: symptoms and causes. https://www.mayoclinic.org/diseases-conditions/constipation/symptoms-causes/syc-20354253
Medical disclaimer: This article is for general education and is not medical advice, diagnosis, or treatment. Talk with a qualified healthcare professional before making significant dietary changes, especially if you have a medical condition, take medication, are pregnant or breastfeeding, or have a weakened immune system.
