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Kefir

Kefir is a probiotic fermented milk drink made with a symbiotic culture of bacteria and yeasts.

Our evidence-based analysis on kefir features 38 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
Last Updated:

Summary of Kefir

Primary information, health benefits, side effects, usage, and other important details

What is kefir?

Kefir is a probiotic fermented milk drink made with multiple cultures of lactic acid bacteria and yeasts. There is no single starter culture, and the bacteria and yeasts vary quite a bit between different brews.[1][2] 

What are kefir's main benefits?

The human clinical trials on kefir to date are all small. Between the small trial sizes and the massive variation in kefirs, there isn’t strong evidence that the kefir available to you will have any given effect on you. On the other hand, if you’re a generally healthy adult, kefir is unlikely to hurt you, and may benefit your oral health.

What are kefir's main drawbacks?

  • Kefir has roughly the same caloric content as the milk it was brewed from, and is often additionally flavored and sweetened.

  • As it contains live, active cultures, kefir should be taken by caution with some.

  • Kefir is lower-lactose than milk, but may still contain enough lactose to trigger symptoms of lactose intolerance.[3]

  • Kefir grains can, rarely, be contaminated with pathogenic fungi or bacteria.[4]

How is kefir taken?

Kefir can be drunk with meals, or alone. Kefir is also used as an ingredient in several cuisines, just as other fermented milk products (yogurt, sour cream) are. When used as a probiotic, kefir shouldn’t be cooked, because that will kill the beneficial bacteria. As with other fermented milk products, there is no recommended daily minimum or maximum for kefir consumption.

How does kefir work?

Many of the bacteria in kefir are known probiotic species.[5] The polysaccharides produced by the kefir cultures may also be bioactive.[6]

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Human Effect Matrix

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The Human Effect Matrix summarizes human studies to tell you what effects Kefir has on your body, how much evidence there is, and how strong these effects are.

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Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Notes
grade-c - High See all 8 studies
Most studies show no effect. Decrease: 1 study (but saw same decrease for plain milk). Increase: 1 study, but only in the female participants. No effect: 6 studies.
grade-c - High See all 8 studies
6 studies found no effect. 2 trials found LDL decreased, but in one, the decrease was not more than milk.
grade-c - Very High See all 8 studies
grade-c - Very High See all 8 studies
The evidence is mixed but leans toward no effect. Only one study found a decrease in triglycerides. Seven other studies found no effect.
grade-d Notable Very High See all 3 studies
Two small studies found that kefir increased the total fecal microbial load.
grade-d Notable - See study
Increased hair loss in chemotherapy patients.
grade-d Notable - See study
Supplementing the standard pharmaceutical therapy for stomach ulcers with kefir gave a higher rate of H.pylori eradication and decreased medication side effects.
grade-d Notable Very High See 2 studies
The two studies which measured this both found a decrease in the kefir group, but evidence is mixed on whether the effect is caused by other dairy: One study saw the same reduction in its milk group, the other didn't see this reduction in its yogurt group.
grade-d Notable Very High See all 3 studies
One study found a significant decrease for those who took 100 mL kefir twice a day, but not those who took it once a day.
grade-d Minor Very High See 2 studies
grade-d Minor Moderate See 2 studies
Mixed evidence. 2 studies measured BMI. One found no change; the other found a decrease, but it wasn't significant compared to unfermented milk.
grade-d Minor Moderate See 2 studies
Kefir decreased the incidence of diarrhea in people taking medicine for stomach ulcers, but not in children taking antibiotics for upper respiratory infections.
grade-d
Minor
Low See all 3 studies
One small study found that kefir consumption increases the amount of probiotic Lactobacillus bacteria in the stool. Another found that kefir didn't significantly change composition compared to milk. A third found that one type of kefir increased the proportion of probiotic bacteria, and another decreased it.
grade-d Minor Moderate See 2 studies
Mixed evidence. One small study found hemoglobin lowered in Crohn's Disease patients who took kefir, but another small study of healthy people didn't find any effect. Needs further research.
grade-d Minor - See study
A small trial of patients with metabolic syndrome noted significantly higher positive affect scores after 3wks of kefir. Needs to be confirmed by further research.
grade-d Minor Moderate See 2 studies
One study found that the incidence of mouth sores during 5-FU chemotherapy was higher in those taking kefir, another found no significant difference.
grade-d Minor Very High See 2 studies
Of the two studies that measured this, one saw a significant decrease, the other didn't see significantly more decrease than cotnrol.
grade-d Minor Low See all 3 studies
Mixed evidence. One study focused on weight loss found WC decreased in kefir group, although not more than it did for milk. Two other studies that measured WC didn't find any change.
grade-d Minor Low See all 3 studies
Mixed evidence. One study focused on weight loss found weight decreased in kefir group, although not more than it did for milk. Two other studies that measured weight didn't find any effect.
grade-d - - See study
grade-d Moderate See 2 studies
Mixed evidence. In a study of overweight people, kefir had no effect on appetite. In a study of chemotherapy patients, those taking kefir were more likely to have the side effect of decreased appetite.
grade-d - - See 2 studies
grade-d - - See 2 studies
grade-d - - See all 3 studies
grade-d - - See study
One study found no effect.
grade-d - Very High See all 4 studies
4 studies found no effect.
grade-d - - See study
grade-d - High See all 3 studies
One small study saw a decrease in CRP among Crohn's patients, but that decrease wasn't significantly different from control.
grade-d - - See study
grade-d
- See all 3 studies
Mixed evidence. In colorectal cancer patients, increase; in children taking antibiotics, no change; and in constipated patients, decrease (uncontrolled trial).
grade-d - - See study
grade-d - - See study
grade-d - Very High See all 4 studies
4 studies which measured this found no effect. This wasn't a primary outcome for any study.
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See all 3 studies
grade-d - - See study
One study found no effect.
grade-d - - See study
grade-d - - See study
grade-d - - See all 3 studies
grade-d - - See all 4 studies
grade-d - - See study
grade-d - Very High See 2 studies
grade-d - - See study
One study found no effect.
grade-d - - See 2 studies
grade-d - - See study
grade-d - - See 2 studies
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See 2 studies
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d Low See all 4 studies
Several clinical trials of kefir measured liver enzymes and found no significant effect, with the exception of a single small trial that found ALT levels decreased by 13 U/L in kefir+exercise group.
grade-d - - See study
Didn't change incidence of loose stools in children taking antibiotics
grade-d - - See study
grade-d - - See study
grade-d - - See 2 studies
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See 2 studies
grade-d - - See study
grade-d - - See all 3 studies
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See 2 studies
grade-d - - See study
grade-d - - See 2 studies
grade-d - - See study
grade-d - - See 2 studies
grade-d - - See study
grade-d - - See study
grade-d - See study
One study provided no to very weak evidence of kefir decreasing zonulin; it needs to be followed up by further research.

Studies Excluded from Consideration

  • Two papers which provide additional analysis, by the same authors, of the data of previously-published studies.[10][11] Their results have been wrapped into the HEM under the first-published studies.

  • One clinical trial of a heat-killed kefir product, which contains no live microorganisms.[12]

  • One poor-quality paper.[13]

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Things to Note

Primary Function:

Also Known As

kefyr, kephir, kefier

Do Not Confuse With

kefiran, water kefir, tibicos, yogurt, kumis

Caution Notice

Kefir contains live probiotics, which should be used with caution by some.

People with compromised health[7], immunocompromised people[8], pregnant people, and people undergoing chemotherapy[9] should consult with a doctor before starting to take a probiotic, such as kefir. So should parents considering giving kefir to infants[8][7] or long-term to children under 5.

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Click here to see all 38 references.