Side by side · Fermented drinks
Kombucha vs kefir: which fermented drink has the evidence?
Both are fizzy fermented drinks, but they start from different things: kombucha from sweet tea, kefir from milk (or sugar water for water kefir). Kefir has a little human evidence; kombucha has nearly none.
By the editors of Alimentotherapy Last reviewed 5 min read Not medical advice
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The short answer
Kefir has the edge on evidence: a small randomized trial found plain kefir improved lactose digestion in adults with lactose maldigestion about as well as yogurt Hertzler 2003. Kombucha has almost no human research: a systematic review found a single published study in people and no registered clinical trialsKapp 2019. Neither has a graded health use on its own, so this page compares them as foods.
Side by side
Grades come from each remedy page and are based on human studies only. How we grade
| Kombucha | Kefir | |
|---|---|---|
| Made from | Sweetened tea and a SCOBY (a mat of bacteria and yeasts) | Milk and kefir grains (bacteria and yeasts); water kefir uses sugar water |
| Human evidence | One published human study (2019 review) | A small lactose trial; part of a fermented-food diet trial |
| Best-supported use | None tested in people | Easier lactose digestion (milk kefir) |
| Alcohol | Can reach 0.5% or more; then regulated as alcohol | Not covered by the sources on this page |
| Home-brew time | 7 to 10 days at 68 to 77°F (tested method) | See our kefir recipes |
| Main safety issue | Contamination if made carelessly; pressure in sealed bottles | Milk allergy; raw-milk versions |
| Who should ask first | Pregnant, immunocompromised, avoiding alcohol | Seriously ill or immunocompromised |
Choose kombucha if
You want a dairy-free fizzy drink to replace soda, you are not pregnant or avoiding alcohol, and you are happy to drink it for the taste rather than for proven benefits.
Choose kefir if
You can have dairy and would like a fermented drink with at least some human evidence behind it, especially if milk itself gives you gas.
Two different ferments
Kombucha is sweetened tea fermented by a SCOBY, a symbiotic culture of bacteria and yeasts. The sugar and yeast drive the fermentation, which can also produce alcohol Ttb. A tested home method from the National Center for Home Food Preservation steeps tea, adds sugar and cools it below 95°F before adding the SCOBY and starter liquid, then ferments it at 68 to 77°F for 7 to 10 days Nchfp.
Milk kefir is milk fermented by kefir grains, clusters of lactic acid bacteria and yeasts held in a matrix of sugars and proteins Bourrie 2016. It is thin, sour and slightly fizzy. Water kefir uses a different kind of grain in sugar water and is dairy-free, so the milk-kefir evidence below does not apply to it.
What the evidence shows
Kombucha. A 2019 systematic review searched three databases and the trial registries and reviewed 310 articles. It found one study reporting results in people and no registered clinical trials. The many health claims made for kombucha come from non-human research Kapp 2019. On our fermented foods page, kombucha is graded not supported for any health outcome for that reason.
Kefir. In a randomized trial in 15 adults with lactose maldigestion, plain kefir lowered breath hydrogen (a sign of undigested lactose) far below milk, about as well as plain yogurt, and cut gas compared with milk Hertzler 2003. Kefir was also one of the foods in the Stanford fermented-food diet, which raised gut microbe diversity and lowered inflammatory markers in a 17-week trial of healthy adults (18 per group) Wastyk 2021. That diet mixed several fermented foods, so it does not show what kefir did alone.
Beyond those, fermented foods may contain live microbes, some similar to strains sold as probiotics, but only a limited number of clinical studies have tested the foods themselves Marco 2017.
Alcohol in kombucha
Because yeasts make alcohol, kombucha can end up with 0.5% or more alcohol by volume. Under federal law, a kombucha that reaches 0.5% at any point during production, when bottled, or after bottling is an alcohol beverage regulated by the Alcohol and Tobacco Tax and Trade Bureau (TTB) Ttb. Home brews are not measured, and a bottle left to keep fermenting can drift upward. If you are pregnant, avoiding alcohol for health or recovery reasons, or giving it to children, keep that in mind.
Safety and home brewing
Kombucha safety steps from the tested method
- Sanitize equipment in hot water (at least 171°F) for at least 30 seconds.
- Check that the starter liquid has a pH of 4.0 or less; if it is higher, do not use it.
- After fermenting, bottle into clean jars, refrigerate promptly and use within 30 days.
- Sealed bottles build up carbon dioxide and can burst if not watched.
All from the National Center for Home Food Preservation Nchfp.
In 1995, CDC reported unexplained severe illness, including one death, in two people in Iowa who had been drinking home-brewed kombucha daily for about two months; the role of the tea was never fully establishedCDC 1995. NCCIH notes that the risk of harm from live microbes is greater in people with severe illness or compromised immune systems NCCIH. If either applies, or you are pregnant, ask your clinician before drinking unpasteurized kombucha or home-brewed kefir.
Kefir is made from milk, so it is off the table with a milk protein allergy, and it should be made from pasteurized milk. The fermentation page covers clean equipment for both.
Making or buying them
Store-bought kombucha and kefir are in most supermarkets; online, iHerb lists kombucha. To brew at home, follow a tested method: our kombucha, milk kefir and water kefir recipes set out the steps.
Common questions
Is kombucha or kefir better for gut health?
Kefir has a little more evidence. A small trial found plain kefir improved lactose digestion, and kefir was part of a fermented-food diet that raised gut microbe diversity in a 17-week Stanford trial. A 2019 systematic review found only one published human study of kombucha and no registered clinical trials.
Does kombucha contain alcohol?
Some does. Fermentation can push kombucha to 0.5% alcohol by volume or more, and under federal law a kombucha that reaches 0.5% at any point is an alcohol beverage regulated by TTB. Home brews are not measured and can vary.
Is homemade kombucha safe?
It can be if you follow a tested method: the National Center for Home Food Preservation calls for sanitized equipment, a starter liquid at pH 4.0 or less, fermenting at 68 to 77°F for 7 to 10 days, then refrigerating and using within 30 days. People who are pregnant or immunocompromised should ask a clinician first.
Sources
Primary research and government sources, each checked on the date this page was reviewed.
- PubMedKapp JM, Sumner W. Kombucha: a systematic review of the empirical evidence of human health benefit. Ann Epidemiol. 2019. PMID 30527803.
- PubMedHertzler SR, Clancy SM. Kefir improves lactose digestion and tolerance in adults with lactose maldigestion. J Am Diet Assoc. 2003. PMID 12728216.
- PubMedWastyk HC, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021. PMID 34256014.
- PubMedBourrie BC, Willing BP, Cotter PD. The microbiota and health promoting characteristics of the fermented beverage kefir. Front Microbiol. 2016. PMID 27199969.
- PubMedMarco ML, et al. Health benefits of fermented foods: microbiota and beyond. Curr Opin Biotechnol. 2017. PMID 27998788.
- PubMedCenters for Disease Control and Prevention. Unexplained severe illness possibly associated with consumption of Kombucha tea, Iowa, 1995. MMWR. 1995. PMID 7476846.
- GuidelineNational Center for Home Food Preservation (University of Georgia). Kombucha Tea.
- SourceAlcohol and Tobacco Tax and Trade Bureau (TTB). Kombucha.
- NCCIHNational Center for Complementary and Integrative Health. Probiotics: Usefulness and Safety.
Keep reading
- RemedyFermented foodsSauerkraut, kimchi, miso, kefir and kombucha. One well-run trial suggests eating more of them changes the gut microbiome; claims beyond that are mostly untested in people.
- RemedyYogurt and kefirCultured milks with the clearest evidence of any fermented food: their live bacteria help digest lactose. Other claims rest on probiotic supplement trials or observational data.
- GoalFood and the gut microbiome: fiber, fermented foods and probioticsMicrobiome science is young. A varied, fiber-rich diet is sensible on many grounds, one small trial found fermented foods raised microbe diversity, and probiotic evidence is strain- and condition-specific.
- How to make itKombuchaSweet tea fermented by a SCOBY. A university-tested recipe now exists, with clear safety steps. The health claims are almost entirely untested in people, and home kombucha is not for everyone.
- ComparisonKefir vs yogurtTwo fermented milks with different microbes: yogurt from two defined bacteria, kefir from grains holding bacteria and yeasts. For lactose, both work about equally in the one trial that compared them. For most other claims, the evidence is thin for both.