Kefir

ProbioticFermented dairy

What is it

Kefir is a fermented milk drink originating in the Caucasus mountains, made by fermenting milk with kefir 'grains' (a symbiotic colony of bacteria and yeasts). It is tangy, slightly effervescent, and rich in live cultures, protein, and B vitamins. Water kefir and dairy-free kefir-style products are also produced.

Evidence for 3 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Lactose intolerance

Good Evidence

Small RCTs show kefir improves lactose digestion versus milk in lactose-intolerant adults.

Gastrointestinal symptoms (general)

Limited Evidence

Modest benefits for bowel regularity and functional GI complaints; effect sizes are small.

Immune support

Limited Evidence

Small trials show modest changes in immune markers; clinical importance unclear.

How it works

Traditional dairy kefir contains a diverse mix of lactic acid bacteria (Lactobacillus, Lactococcus, Leuconostoc), acetic acid bacteria, and yeasts (Kluyveromyces, Saccharomyces). This diversity is broader than yogurt and includes species that can transiently colonize the gut and modulate the microbiome. Reported health effects include improved lactose tolerance (microbes break down lactose during fermentation), modest improvements in GI symptoms, and possible immunomodulatory effects. Trial quality and effect sizes vary; many trials use specific commercial products that may not generalize to all kefir.

Dosage

No RDA. Clinical trials commonly use 200-500 mL/day. Probiotic counts are typically 10^9-10^10 CFU per cup, varying widely by product and freshness.

When and how to take it

Consumed as a daily food, with or between meals. No evidence-based time-of-day preference.

2 commercial forms

Compare the main delivery options and what they’re best suited for.

Traditional dairy kefir

Most studied form.

Live cultures generally survive transit; some die in stomach acid.

Water kefir / coconut kefir

Dairy-free option.

Different microbial profile from dairy kefir.

Safety

Generally safe and well tolerated. Mild GI symptoms (gas, bloating) can occur in the first 1-2 weeks. Rare cases of infection in critically ill or severely immunocompromised people have been reported with probiotic products in general.

Who should be cautious

Severely immunocompromised people and those with central venous catheters should consult a clinician. People with milk allergy must avoid dairy kefir. Pregnancy and breastfeeding are compatible with pasteurized commercial kefir.

Interactions

Calcium and casein in dairy kefir can reduce absorption of certain antibiotics, bisphosphonates, and levothyroxine; separate by 2-4 hours.

Documented interactions

Evidence-graded pair pages with sources, dosing notes, and timing guidance — a complement to the narrative section above.

Warnings (1)

+ antibiotics

low

Antibiotics can kill the live bacteria and yeast in kefir if both are taken at the same time, and dairy calcium can bind certain antibiotics (tetracyclines, fluoroquinolones) and reduce their absorption. Spacing kefir a couple of hours away from each dose addresses both concerns. Note that the broader claim that kefir prevents antibiotic-associated diarrhea is not well supported: the one randomized trial of kefir itself found no benefit.

See all 1 Kefir interaction →

Food sources

Plain dairy kefir

Amount
100-130 kcal, 8-11g protein per cup
%DV
—

Frequently asked questions

Is kefir better than yogurt?⌄

Kefir has more microbial diversity than yogurt, including some yeast species. Both contribute live cultures.

Can I drink kefir if I'm lactose intolerant?⌄

Often yes. Fermentation reduces lactose, and many lactose-intolerant people tolerate kefir better than milk.

References

Kefir on Wikidata — Wikidata link

Kefir on NIH DSLD (US supplement label database) — NIH Dietary Supplement Label Database link

Research on Kefir (PubMed search) — PubMed link

Track Kefir with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.