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Kefir

Kefir is a probiotic fermented milk drink made with a symbiotic culture of bacteria and yeasts. It may benefit oral health, may be a useful adjunct to stomach ulcer treatment, and may offer slight benefits to blood sugar. On the other hand, drinking kefir makes chemo side effects worse for some cancer patients. Since it contains live, active bacteria and yeasts, kefir should be used with caution by anyone with a compromised or weakened immune system.

Our evidence-based analysis on kefir features 40 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
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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 whichever kefir you take 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.

Kefir may also be a useful adjunct to a common treatment for stomach ulcers, and for people with type 2 diabetes, regular kefir consumption may give slight improvements to blood sugar and glycated hemoglobin (but not enough to be considered a treatment).

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 with caution by 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
8 studies found no effect.
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 - See study
One study of cancer survivors in an exercise program saw a greater decrease in depression scores with kefir than with no supplement.
grade-d Notable - See study
A study of patients undergoing chemotherapy for colorectal cancer found that kefir increased incidence of difficulty swallowing.
grade-d Notable - See study
A study of patients undergoing chemotherapy for colorectal cancer found that kefir increased incidence of drowsiness.
grade-d Notable - See study
A study of patients undergoing chemotherapy for colorectal cancer found that kefir increased incidence of dry mouth.
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
A study of cancer survivors in an exercise program saw a decrease in a pooled GI distress score with kefir.
grade-d Notable - See study
Increased hair loss in chemotherapy patients.
grade-d Notable - See study
In one study, patients taking standard drug therapy for H. pylori infection experienced less headaches with kefir.
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 - See study
One study saw a notable increase in the percentage of circulating leukocytes that were monocytes
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 - See study
One trial in people with metabolic syndrome saw a decrease in oxidized LDL in the kefir 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 Notable - See study
In patients undergoing chemotherapy for colorectal cancer, those who took kefir experienced less difficulty sleeping.
grade-d Notable Moderate See 2 studies
Mixed evidence. A study of 42 type 2 diabetics found a notable decrease in kefir group. But a study in healthy young men found no effect.
grade-d Notable - See study
One study of patients undergoing chemotherapy for colorectal cancer found that those who took kefir were more likely to experience weight loss.
grade-d Minor Very High See 2 studies
2 studies: Patients taking medicine for H. pylori infections had notably less abdominal pain with kefir. Patients with CD had less abdominal pain, but the difference wasn't significant.
grade-d Minor Very High See 2 studies
Two studies of people with metabolic syndrome noted a modest decrease in systolic and diastolic blood pressure, although it wasn't significantly different than milk control in one trial.
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 - See study
One study in cancer survivors saw an increase in the percentage of monocytes that were classical monocytes.
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 Very High See all 3 studies
Effects may be limited to people with Type 2 diabetes. Two trials of Type 2 diabetic patients found modest reductions in fasting blood glucose, but while a small trial of people with metabolic syndrome did find a reduction, it wasn't significantly different from yogurt control.
grade-d Minor - See study
In one study, cancer survivors in an exercise program saw a greater decrease in fatigue scores with kefir.
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 - See study
One study found that kefir increased total fecal SCFA, but so did milk, with no significant difference.
grade-d Minor - See study
grade-d Minor Moderate See all 4 studies
Mixed evidence: two studies found no effect, two found a decrease.
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 Moderate See 2 studies
Mixed evidence. A 22-person study in people with metabolic synrome found no effect. But a 60-person study in diabetic patience found a modest decrease.
grade-d Minor - See study
One study found a decrease with both kefir and milk control - no significant difference between milk & kefir
grade-d Minor - See study
One non-controlled study found an increase in IL-5 during kefir consumption.
grade-d Minor - See study
One non-controlled study found a decrease in IL-8 during kefir consumption.
grade-d Minor Moderate See 2 studies
Mixed evidence. Cancer survivors in an exercise program saw a greater increase in lean mass with kefir than with no supplement; however, a study in people with metabolic syndrome, with no exercise, saw no significant change in lean mass compared to yogurt control.
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
- See 2 studies
Patients undergoing chemotherapy were more likely to have nausea, but patients taking medicine for ulcers were less likely to have nausea.
grade-d Minor - See study
One study in cancer survivors saw a decrease in the percentage of monocytes that were non-classical.
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 - See 2 studies
Mixed evidence. In a study of patients undergoing chemotherapy for colorectal cancer, those who took kefir experienced more side effects and self-reported lower quality of life. Another study, of cancer survivors in an exercise program, didn't find that kefir had any effect.
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 - See study
One study, in diabetic patients, found an increase but not significantly different from milk control.
grade-d Minor - See study
In one study, cancer survivors in an exercise program saw a greater decrease in serum lipopolysaccharides with kefir than with no supplement.
grade-d Minor - See study
In a study of patients undergoing chemotherapy for colorectal cancer, more of those who took kefir experienced the sweats.
grade-d Minor - See study
One study found a decrease
grade-d Minor Moderate See 2 studies
Mixed evidence. Patients undergoing chemo for colorectal cancer experienced more vomiting with kefir, but children taking antibiotics saw no effect.
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 4 studies
Mixed evidence. One study focused on weight loss found weight decreased in kefir group, although not more than it did for milk. Three other studies that measured weight didn't find any effect.
grade-d - - See study
1 study in overweight people found no effect.
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
Mixed evidence. In patients receiving chemotherapy, kefir increased bloating. A small study of patients with IBS found that Crohn's patients self-reported bloating reduced after two weeks of kefir, but the study didn't report the values.
grade-d Low See all 3 studies
Only 1 of 3 studies found a decrease. Not to be confused w/ fasting glucose, see separate entry in HEM.
grade-d - - See study
One study found no effect.
grade-d - Very High See all 5 studies
5 studies found no effect.
grade-d - - See study
One study found no significant difference between control and kefir
grade-d - High See all 4 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
One study found no effect.
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
No significant effect on cough among children taking antibiotics for an upper respiratory infection.
grade-d - - See study
One study found no effect.
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
One study found no effect.
grade-d - Very High See all 3 studies
3 studies found no effect.
grade-d - Very High See 2 studies
2 studies found no effect.
grade-d - - See study
One study found no effect.
grade-d - - See study
One trial in people with metabolic syndrome found no effect.
grade-d Moderate See 2 studies
Mixed leaning toward no effect. A trial of 60 diabetic patients saw no effect; a trial of 22 patients with metabolic syndrome saw a decrease in the kefir group, but not significantly more than milk control.
grade-d - - See study
One study found no effect
grade-d - - See study
A study in colon cancer patients found no effect
grade-d - - See study
One study found no effect
grade-d - Very High See all 3 studies
Three studies found no effect.
grade-d - - See study
One study in cancer survivors saw no change in the proportion of monocytes that were of intermediate type
grade-d - - See study
A study of children taking antibiotic therapy found kefir had no effect on incidence of irritability.
grade-d - - See study
A study of children taking antibiotic therapy found kefir had no effect on incidence of lethargy.
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
No significant effect on "runny nose" among children taking antibiotics for an upper respiratory infection.
grade-d - - See study
One study found no effect
grade-d - - See study
grade-d - - See study
One study found no effect.
grade-d - - See study
One study found no effect.
grade-d - - See study
One study found no effect.
grade-d - - See study
One study found no effect.
grade-d - - See study
One study found no effect.
grade-d - - See study
One study found no effect.
grade-d - - See study
One study found no effect.
grade-d - - See study
One study found no effect.
grade-d - - See study
One study found no effect.
grade-d - - See study
One small non-controlled study found no effect.
grade-d - - See study
No significant effect on stomach pain among children taking antibiotics for an upper respiratory infection.
grade-d
- See 2 studies
Mixed evidence: In a study of patients undergoing chemotherapy, decrease; in a small study of patients with IBD, those with Crohn's reported an increase, but not those with UC.
grade-d
- See all 4 studies
Mixed evidence. Of four studies, one saw an increase with kefir, two saw no effect, and one saw a decrease that wasn't significantly different from milk control.
grade-d - - See study
One study of endurance training found that drinking kefir post-training didn't affect time to go 1.5 miles.
grade-d - - See study
One study found no effect.
grade-d - Very High See 2 studies
Two studies found no effect.
grade-d - - See study
One study found no effect.
grade-d - - See study
One trial in overweight people found no effect.
grade-d - - See study
One study found no effect.
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, labneh

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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