Functional Foods · Fermented food
Kefir
Fermented milk drink (kefir grains) · also called Milk kefir, kéfir
Kefir is a tangy fermented milk drink made with kefir grains. It gives protein and calcium like other dairy. Small trials suggest it is easier on lactose than milk and may add to H. pylori treatment, while pooled trials show no clear effect on blood pressure or cholesterol. The main cautions are milk allergy, a weakened immune system, and unpasteurised dairy in pregnancy.
General information, not medical advice. Last substantive update · Not medically reviewed. A named clinician has not signed off on this page. How this page is made
About Kefir
Kefir is a fermented milk drink with the nutrients of milk plus live bacteria and yeasts. It is a food, not a proven remedy. Small trials suggest it may help with lactose and add to H. pylori treatment, while pooled trials show no clear effect on blood pressure or cholesterol.
What it is
Kefir is a traditional fermented-milk drink made with kefir grains. A 2021 analysis describes it as made by lactic-alcoholic fermentation of milk, which is why it can contain a little alcohol. This page covers milk kefir only. Water kefir, plant-milk kefirs and kefir supplements are different products.
USDA data for one plain lowfat product, per 100 g: 43 kcal, 3.79 g protein, 1.02 g fat, 4.77 g carbohydrate (3.7 g of it lactose), 130 mg calcium, 105 mg phosphorus, 164 mg potassium, 40 mg sodium, 0.135 mg riboflavin and 0.29 ug vitamin B12. A cup (243 g) has about 104 kcal, 9.2 g protein, 316 mg calcium and 11.2 g of sugars. Brands, fat levels and added sugar change these numbers, so check the label.
Fermented food or probiotic?
The ISAPP expert panel defines fermented foods as foods made through desired microbial growth and enzymatic conversions of food components, and says they are not automatically probiotics. Kefir has live microbes, and in some studies kefir bacteria were found in stool. Whether a product still has live microbes depends on how it was made, so the label matters. Several of the panel's authors report paid work for dairy, food and probiotic companies.
What the research shows
A 2023 review of randomised trials found 16 studies of milk kefir. The authors say it may have potential in H. pylori treatment and for a mouth bacterium linked to tooth decay, and call the evidence for blood pressure and cholesterol very limited. Twelve of the 16 studies had a high risk of bias.
Lactose: in 15 adults who digest lactose poorly, plain kefir gave about a third of the breath hydrogen of milk, and kefir and yogurt both cut perceived gas. That is one small trial from 2003.
H. pylori: in 82 patients on standard triple therapy, clearance was 78.2% with kefir and 50.0% with a milk placebo. That is one small trial.
Heart and metabolism: a 2025 pooled analysis of 7 trials found no significant change in blood pressure or CRP overall. A 2023 pooled analysis found lower insulin and insulin resistance but no effect on LDL, other cholesterol, fasting blood sugar, HbA1c or weight. A 2021 analysis did find lower fasting blood sugar, so the results disagree.
Gut: a 2026 review of 8 studies found modest, varied changes in gut bacteria. In young children given antibiotics, kefir did not prevent diarrhea (18% versus 21.9%).
Food versus other products
Every result above is for milk kefir drunk as a food. Water kefir, plant-milk kefir, kefir-derived probiotic mixtures and kefir supplements are different products, and their results should not be borrowed for kefir. One 2026 trial used lactose-free kefir, which is also a different product.
At a glance
Traditional uses history, not proof
- Drunk as a traditional fermented-milk drink
- Long use as a food is not proof that it treats any condition
Studied for research
- Protein and calcium, high certainty for the nutrient content of one product
- Lactose digestion, low certainty (one small trial)
- Gut bacteria and gut comfort, low certainty
- H. pylori treatment as an add-on, low certainty
- Blood sugar and insulin, mixed
- Blood pressure and cholesterol, low certainty, no clear effect
- Antibiotic diarrhea in young children, no benefit found
- Bone density, insufficient evidence
Main compounds
- Protein
- Lactose (milk sugar)
- Calcium
- Live bacteria and yeasts
Common forms
- Plain lowfat milk kefir (the USDA entry read)
- Whole-milk, flavoured and sweetened kefir (values not read)
- Lactose-free kefir (used in one 2026 trial)
- Water kefir, plant-milk kefir and kefir supplements are different products and are not covered
Research links: 2023 review: kefir trials in people (16 studies) · 2003 trial: kefir and lactose digestion · 2025 analysis: kefir, blood pressure and CRP · Research Library · Genes & Biomarkers Library
What it is and its history
- Accepted scientific name
- Kefir (fermented milk drink made with kefir grains)
- Naming authority
- A food, not a single species; no taxonomy entry applies.
- Common names
- Kefir (English); Milk kefir (English); Kéfir (Spanish)
- Family or group
- Fermented dairy foods
- Native range
- Not verified from a source read.
- Cultivation
- Not verified from a source read.
- Harvest and processing
- A 2021 meta-analysis describes kefir beverage as obtained by lactic-alcoholic fermentation of milk using kefir grains or a starter culture. The 2023 review calls it a traditional fermented-milk beverage. Retail processing and pasteurisation were not researched.
- Look-alikes and adulterants
- Name: Water kefir; Note: A different, non-dairy ferment made from sugar water; it has its own page and the milk kefir trials do not transfer to it.; Name: Yogurt; Note: A fermented milk with different cultures; the 2003 lactose trial compared the two.; Name: Kefir supplements and probiotic capsules; Note: Not the same as the drink; not covered.
Photographs
What is inside, and how it may work
What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.
Main compounds
| Compound | Family | Where it is concentrated | Activity studied | Level of evidence |
|---|---|---|---|---|
| Protein | macronutrient | Milk USDA, one plain lowfat product: 3.79 g per 100 g | Nutrient source. 21 | Human data |
| Lactose | milk sugar | Milk USDA, one plain lowfat product: 3.7 g per 100 g | Digested by the enzyme lactase; undigested lactose causes gas in lactose maldigestion. 21 6 | Human data |
| Calcium | mineral | Milk USDA: 130 mg per 100 g | Nutrient source; absorption from kefir was not researched. 21 | Human data |
| Live bacteria and yeasts | microbes | Whole drink Not given in sources read | Kefir-specific bacterial species were found in stool in some trials, which the 2026 review takes to suggest colonisation. Counts depend on the product and whether it is heated after fermentation. 5 4 | Human data |
Mechanisms, receptors and pathways
| Target or pathway | Gene or receptor | What was found | Level |
|---|---|---|---|
| Lactose digestion | Lactase (not measured) | Kefir gave much less breath hydrogen than milk in 15 adults with lactose maldigestion. The authors conclude kefir improved lactose digestion; the abstract does not test why. 6 | Human data |
| Gut microbiota | Not specified | Kefir caused modest, varied changes in gut bacteria; kefir-specific bacteria were found in stool. Direct functional evidence in people is limited. 5 4 | Human data |
Absorption, metabolism and elimination
- Absorption
- Not researched for kefir nutrients in people.
- Distribution
- Not found.
- Metabolism
- Not found.
- Elimination
- Not found.
- Bioavailability
- Not established for kefir calcium in the sources read.
Isolated compounds versus whole extracts
All the human results here are for kefir as a milk drink. Water kefir, plant-milk kefir, kefir-derived probiotic mixtures and kefir supplements are different products, and a fermented food is not automatically a probiotic (ISAPP).
Nutritional composition
Nutrition from USDA FoodData Central (SR Legacy, April 2018 release; values read 2026-10-26 from a saved copy of the data, because the public API was rate-limited). One branded product: Kefir, lowfat, plain (FDC 170904). Per 100 g: 43 kcal, 3.79 g protein, 1.02 g fat (0.658 g saturated), 4.77 g carbohydrate (4.61 g sugars, 3.7 g of it lactose), 130 mg calcium, 164 mg potassium, 105 mg phosphorus, 40 mg sodium, 12 mg magnesium, 0.46 mg zinc, 3.6 ug selenium, 0.135 mg riboflavin, 0.29 ug vitamin B12, 1 ug vitamin D, 171 ug vitamin A (RAE), 89.7 g water. One typical USDA portion is 1 cup (243 g; the 100 g values multiplied by 2.43): about 104 kcal, 9.2 g protein, 2.5 g fat (1.6 g saturated), 11.6 g carbohydrate (11.2 g sugars, about 9 g of it lactose), 316 mg calcium, 398 mg potassium, 255 mg phosphorus, 97 mg sodium, 0.33 mg riboflavin, 0.70 ug vitamin B12 and 2.4 ug vitamin D. Whole-milk, flavoured, sweetened and plant-milk kefirs differ; check the label.
1 high certainty1 mixed findings8 low certainty2 not enough evidence
What was looked at
The 12 benefits and uses checked for Kefir, each with how strong the evidence is. Tap one to open it.
- Protein, calcium and vitamins (nutrient content)High certainty
- Lactose digestion and toleranceLow certainty
- Gut bacteria and gut comfortLow certainty
- Helicobacter pylori treatment (as an add-on)Low certainty
- Blood sugar and insulin resistanceMixed findings
- Blood pressure and inflammation (CRP)Low certainty
- Cholesterol and blood fatsLow certainty
- Mouth bacteria (Streptococcus mutans) and tooth decayLow certainty
- Diarrhea during antibiotics in young childrenLow certainty
- Body weight and waistLow certainty
- Bone density and bone turnoverNot enough evidence
- Sleep and mental well-beingNot enough evidence
Lab markers tracked in the studies
Breath hydrogenFasting insulin and HOMA-IRBlood pressureLDL cholesterolBody weightBone mineral density
What is Kefir good for?
The main studied uses and how strong the human evidence is for each. All results are for milk kefir as a drink. Most trials are small, and some outcomes are blood tests rather than health outcomes.
Benefits, one by one
Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.
Protein, calcium and vitamins (nutrient content)
High certaintyPlain lowfat kefir is a source of protein, calcium, phosphorus and riboflavin. One cup (243 g) has about 9 g of protein and 316 mg of calcium by USDA data for one branded product.
1 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
No trial was read showing that drinking kefir corrects a nutrient shortfall.
Results
Kefir is a dairy drink with the nutrients of milk. The values below are for one branded plain lowfat product and will differ by brand, fat level and added sugar.
Effect sizes as reported
USDA FDC 170904 per 100 g: 43 kcal, 3.79 g protein, 130 mg calcium, 105 mg phosphorus, 0.135 mg riboflavin, 0.29 ug vitamin B12, 1 ug vitamin D, 40 mg sodium. Per cup (243 g): about 104 kcal, 9.2 g protein, 316 mg calcium, 0.70 ug B12, 11.2 g sugars.
Why this rating
High that the product contains these nutrients (USDA data for one product). Not tested as a treatment for any shortfall.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered.
Who was studied
General diet.
Limits
Nutrient facts for one branded plain lowfat product; flavoured and whole-milk kefir differ and added sugar can be high.
Why researchers looked
People drink kefir as a dairy food, so its nutrients matter.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Nutrient database
These are nutrient amounts in the food, taken from a USDA table.
A proposed mechanism does not show that the effect happens in people.
Contains milk and lactose; see the Safety tab.
Lactose digestion and tolerance
Low certaintyIn a small 2003 crossover trial of 15 adults who digest lactose poorly, plain kefir gave far less breath hydrogen than milk with the same amount of lactose, and kefir cut the perceived severity of gas.
2 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
Randomised block design in 15 adults, each given 20 g lactose in milk, plain or raspberry kefir, or plain or raspberry yogurt, with hourly checks for 8 hours.
Results
Plain kefir and plain yogurt both gave about a third of the breath hydrogen seen with milk. Flavoured kefir was in between. Pain and diarrhea were negligible with all meals.
Effect sizes as reported
Breath hydrogen AUC: milk 224 ppm x h; plain kefir 87; plain yogurt 76; flavoured kefir 156. Perceived flatulence severity 54 to 71% lower than with milk.
Why this rating
Low: one small, old trial of single test meals. Breath hydrogen is a sign, not a long-term outcome. Plain yogurt did about as well.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered.
Who was studied
Healthy adults with lactose maldigestion.
Limits
15 people; single meals; no long-term follow-up; flavoured kefir did less well.
Why researchers looked
Kefir still contains lactose, but fermentation and live microbes may help it be digested.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Authors interpretation
The authors say kefir improved lactose digestion. The reason was not tested in the abstract.
A proposed mechanism does not show that the effect happens in people.
Kefir still has lactose. Milk allergy is a different problem and kefir is not safe for it.
Gut bacteria and gut comfort
Low certaintyA 2026 review of 8 human studies found modest, varied changes in gut bacteria with kefir, and kefir bacteria turning up in stool. A 2026 trial in 65 healthy young adults reported fewer gut symptoms after 6 weeks of lactose-free kefir.
3 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
The 2026 review (8 studies) found minor changes at phylum and class level and a rise in Bifidobacterium in 3 of 4 studies. The 2026 J Nutr trial (65 volunteers, 250 mL lactose-free kefir a day for 6 weeks) found fewer gut symptoms, but the abstract does not say what the comparison group received.
Results
Changes in gut bacteria are small and not consistent, and it is not known whether they matter for health. Gut symptoms improved in one small trial of healthy young adults.
Effect sizes as reported
Review: Bifidobacterium up in 3 of 4 studies. Trial: gut symptoms decreased (P<0.05); immunity and inflammation markers not significantly improved.
Why this rating
Low: small studies of mixed design, healthy people, and a change in bacteria is not a health outcome.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered. The 2026 trial used lactose-free kefir.
Who was studied
Mostly healthy adults.
Limits
Mixed designs, small samples, many outcomes tested. A fermented food is not automatically a probiotic.
Why researchers looked
Kefir carries live bacteria and yeasts, so researchers ask whether it changes the gut.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Authors interpretation
Proposed: kefir microbes pass through and may briefly persist, and the authors suggest this could change the gut environment. Direct proof of function in people is limited.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab for weakened immunity.
Helicobacter pylori treatment (as an add-on)
Low certaintyIn one randomised trial of 82 patients, adding kefir to 14 days of standard triple therapy went with a higher H. pylori clearance (78.2% versus 50.0%). It was an add-on to medicine, not a replacement.
2 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
A randomised, double-blind trial gave 250 mL of kefir or milk with placebo twice a day for 14 days alongside lansoprazole, amoxicillin and clarithromycin. Breath tests were repeated at 45 days. The 2023 review called kefir potentially useful as an add-on but with limited evidence.
Results
More patients cleared the infection with kefir, and side effects were fewer and milder.
Effect sizes as reported
Eradication 36 of 46 (78.2%) with kefir versus 18 of 36 (50.0%) with placebo, P = .026.
Why this rating
Low: one small trial in one setting, unequal groups, and the review rates the overall evidence as limited.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered. 250 mL twice daily in this trial; this is a study detail, not advice.
Who was studied
Adults with dyspepsia and confirmed H. pylori.
Limits
One small trial. Never stop prescribed treatment.
Why researchers looked
Probiotics have been studied as add-ons to H. pylori treatment, and kefir contains live microbes.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Not tested
Not shown in the abstract.
A proposed mechanism does not show that the effect happens in people.
Do not stop or change prescribed treatment.
Blood sugar and insulin resistance
Mixed findingsTwo pooled analyses of about 6 small trials each disagree. One found lower fasting blood sugar and insulin; the other found lower insulin and insulin resistance (HOMA-IR) but no fasting blood sugar effect. HbA1c did not change significantly in either.
2 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
2021 meta-analysis (6 trials, 323 people): fasting blood sugar WMD -10.28, insulin WMD -2.87, HbA1c not significant. 2023 meta-analysis (6 trials, 314 people): fasting insulin -3.69 micro-IU/mL, HOMA-IR -2.56, fasting blood sugar and HbA1c not significant.
Results
A possible lowering of insulin and insulin resistance, and an unclear effect on fasting blood sugar. HbA1c, the long-term marker, did not change significantly.
Effect sizes as reported
Insulin WMD -3.69 micro-IU/mL (95% CI -6.30 to -1.07); HOMA-IR -2.56 (-3.82 to -1.30); HbA1c p = 0.339 (2023); HbA1c -0.64 (-1.36 to 0.08) (2021).
Why this rating
Mixed: the two analyses disagree on fasting blood sugar, trials are few and small, and doses and lengths varied.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered.
Who was studied
Adults, including people with diabetes or metabolic problems (population mix not given in the abstracts).
Limits
Overlapping small trials; results differ by analysis. Not a treatment for diabetes.
Why researchers looked
Fermented dairy has been studied for blood sugar and insulin.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Not tested
Not established; the abstracts do not test a mechanism.
A proposed mechanism does not show that the effect happens in people.
People with diabetes should follow their own care plan.
Blood pressure and inflammation (CRP)
Low certaintyA 2025 pooled analysis of 7 trials (385 adults) found no significant fall in blood pressure or in C-reactive protein overall. A subgroup of trials lasting 8 weeks or more did show a CRP fall.
2 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
7 randomised trials, at least 2 weeks each, with random-effects pooling. The 2023 narrative review had said kefir may further aid hypertension treatment but called the evidence very limited.
Results
No significant effect on systolic or diastolic blood pressure or CRP overall. The CRP subgroup finding is exploratory.
Effect sizes as reported
Systolic -1.76 mmHg (95% CI -5.21 to 1.69); diastolic -1.19 mmHg (-3.40 to 1.03); CRP -0.17 mg/L (-0.84 to 0.49).
Why this rating
Low (no clear effect): few small trials; the longer-trial CRP result may be chance.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered.
Who was studied
Adults.
Limits
Few trials; subgroup analysis.
Why researchers looked
Fermented milks have been studied for blood pressure, and kefir for inflammation.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Not tested
Not tested in the abstract.
A proposed mechanism does not show that the effect happens in people.
If you take blood pressure medicine, keep taking it as prescribed.
Cholesterol and blood fats
Low certaintyPooled trials found no effect of kefir on total, LDL or HDL cholesterol or triglycerides, and a small 2002 crossover trial of 13 men found the same versus milk.
4 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
2023 meta-analysis (6 trials, 314 people): no effect on total cholesterol (p 0.088), LDL (p 0.910), HDL (p 0.491) or triglycerides (p 0.824). 2002 crossover trial: no effect of kefir versus milk after 4 weeks. The 2023 narrative review had said evidence for dyslipidemia was very limited.
Results
No clear effect on blood fats. One 2026 trial of lactose-free kefir in young adults reported lower serum cholesterol, but it tested many outcomes in a small group.
Effect sizes as reported
LDL p = 0.910 (pooled); 2002 trial: no change in total, LDL, HDL or triglycerides.
Why this rating
Low (evidence leans against an effect): the pooled trials are few and small, and one 2026 trial points the other way.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered.
Who was studied
Adults, including mildly hypercholesterolemic men.
Limits
Small trials; short; mostly 4 to 8 weeks.
Why researchers looked
Fermented milks have been studied for cholesterol.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Not tested
Not shown.
A proposed mechanism does not show that the effect happens in people.
Follow your own clinician's plan for cholesterol.
Mouth bacteria (Streptococcus mutans) and tooth decay
Low certaintyThe 2023 review says kefir may have potential for lowering Streptococcus mutans in the mouth, a bacterium linked to tooth decay. No source read showed fewer cavities.
1 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
From the review summary only: the authors judge fermented-milk kefir may have potential to lower oral S. mutans and so reduce decay risk. The individual dental trials were not read.
Results
A change in a mouth bacterium, not in cavities.
Effect sizes as reported
No numbers in the review abstract.
Why this rating
Low, summary-only: we read the review abstract, not the dental trials.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered.
Who was studied
Not given in the abstract.
Limits
Not read at trial level. A lower bacteria count is not fewer cavities.
Why researchers looked
Kefir has been tested as a rinse or drink for mouth bacteria.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Not tested
Not described in the abstract.
A proposed mechanism does not show that the effect happens in people.
Kefir can contain sugar (flavoured types) and acid; ask a dentist about your own teeth.
Diarrhea during antibiotics in young children
Low certaintyIn a trial of 125 children aged 1 to 5 on antibiotics, kefir did not prevent diarrhea: 18% had it with kefir and 21.9% with placebo.
1 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
Double-blind, placebo-controlled (heat-killed placebo), 14-day follow-up, primary care in the US.
Results
No difference in diarrhea or in any secondary outcome. The authors saw interactions with age, sex and starting health that need more study.
Effect sizes as reported
18% vs 21.9%, relative risk 0.82 (95% CI 0.54 to 1.43).
Why this rating
Low (no benefit found): one trial, young children only, a wide confidence interval.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered. A commercial kefir drink.
Who was studied
Children aged 1 to 5.
Limits
One trial; the interval includes both a benefit and a harm.
Why researchers looked
Probiotics have shown some promise for antibiotic-associated diarrhea, so kefir was tested.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Not tested
Not applicable.
A proposed mechanism does not show that the effect happens in people.
Ask a doctor before giving kefir to a young child with diarrhea.
Body weight and waist
Low certaintyIn one 8-week trial of 75 overweight women, extra servings of kefir or of milk both led to more weight loss than the control diet, and kefir did no better than milk.
2 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
Randomised, three groups: control, milk, kefir. The 2023 pooled analysis of cardiometabolic factors found no effect of kefir on body weight (p = 0.439).
Results
Kefir and milk were similar. The result is about dairy servings, not something special in kefir.
Effect sizes as reported
Kefir vs milk: no significant difference.
Why this rating
Low: one trial of 75 women (58 finished) and a pooled analysis showing no effect on weight.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered.
Who was studied
Overweight or obese premenopausal women.
Limits
Short; many dropouts.
Why researchers looked
Dairy intake has been studied for weight.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Not tested
Not tested.
A proposed mechanism does not show that the effect happens in people.
None specific.
Bone density and bone turnover
Not enough evidenceA small 2015 pilot trial in 40 people with osteoporosis reported short-term changes in bone markers and larger 6-month hip bone density gains with kefir plus calcium than with calcium alone.
1 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
Double-blind parallel pilot over 6 months in 40 people with osteoporosis. Bone density by DXA at the spine, hip and femoral neck. The kefir group also got calcium carbonate.
Results
The authors report greater hip density increases and some marker changes. Parathyroid hormone rose with kefir and fell in the control group. The abstract gives no between-group numbers.
Effect sizes as reported
No numbers in the abstract.
Why this rating
Insufficient: a single pilot of 40 people with no between-group numbers in the abstract.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered.
Who was studied
People with osteoporosis.
Limits
Pilot; the kefir arm also had calcium; not a treatment for osteoporosis.
Why researchers looked
Dairy is a calcium source, and kefir peptides were suggested to help calcium uptake.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Authors interpretation
The authors describe kefir peptides with calcium-absorption bioactivities; not tested in this trial.
A proposed mechanism does not show that the effect happens in people.
Keep taking prescribed osteoporosis treatment.
Sleep and mental well-being
Not enough evidenceIn the 2026 trial of 65 healthy young adults, sleep and mental health scores moved in a good direction but not significantly.
1 studiesMilk kefir as a drink (commercial or trial product). Water kefir, pla…
Studies, doses and limits
What the trials found
6 weeks of 250 mL lactose-free kefir a day; the abstract does not say what the comparison group received.
Results
No significant improvement in sleep, mental health, immunity or inflammation markers.
Effect sizes as reported
P > 0.05 for sleep, mental health, glucose and CRP.
Why this rating
Insufficient: not significant in one small trial.
Form and dose studied
Milk kefir as a drink (commercial or trial product). Water kefir, plant-milk kefirs and kefir supplements are different products and are not covered. Lactose-free kefir.
Who was studied
Healthy young adults.
Limits
Small; many outcomes tested.
Why researchers looked
The gut and mood are linked, so these were measured.
Traditional use
Kefir is a traditional fermented-milk drink. Long use as a food is not proof that it treats any condition.
Proposed mechanism Not tested
Not tested.
A proposed mechanism does not show that the effect happens in people.
None specific.
Connections to the rest of health
How Kefir connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.
Explore every connection: goals, body systems, organs, symptoms, genes
A. Wellness goals
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Preventive Wellness | High certainty | Protein, calcium and vitamins (nutrient content): Plain lowfat kefir is a source of protein, calcium, phosphorus and riboflavin. One cup (243 g) has about 9 g of protein and 316 mg of calcium by USDA data for one branded product. | 21 | |
| Digestive Support | Low certainty | Lactose digestion and tolerance: In a small 2003 crossover trial of 15 adults who digest lactose poorly, plain kefir gave far less breath hydrogen than milk with the same amount of lactose, and kefir cut the perceived severity of gas. Helicobacter pylori treatment (as an add-on): In one randomised trial of 82 patients, adding kefir to 14 days of standard triple therapy went with a higher H. pylori clearance (78.2% versus 50.0%). It was an add-on to medicine, not a replacement. | 6 20 2 7 | |
| Gut Health | Low certainty | Gut bacteria and gut comfort: A 2026 review of 8 human studies found modest, varied changes in gut bacteria with kefir, and kefir bacteria turning up in stool. A 2026 trial in 65 healthy young adults reported fewer gut symptoms after 6 weeks of lactose-free kefir. | 5 1 8 | |
| Microbiome Balance | Low certainty | Gut bacteria and gut comfort: A 2026 review of 8 human studies found modest, varied changes in gut bacteria with kefir, and kefir bacteria turning up in stool. A 2026 trial in 65 healthy young adults reported fewer gut symptoms after 6 weeks of lactose-free kefir. | 5 1 8 | |
| Blood Sugar Balance | Mixed findings | Blood sugar and insulin resistance: Two pooled analyses of about 6 small trials each disagree. One found lower fasting blood sugar and insulin; the other found lower insulin and insulin resistance (HOMA-IR) but no fasting blood sugar effect. HbA1c did not change significantly in either. | 11 14 | |
| Metabolic Health | Mixed findings | Blood sugar and insulin resistance: Two pooled analyses of about 6 small trials each disagree. One found lower fasting blood sugar and insulin; the other found lower insulin and insulin resistance (HOMA-IR) but no fasting blood sugar effect. HbA1c did not change significantly in either. | 11 14 | |
| Heart Health | Low certainty | Blood pressure and inflammation (CRP): A 2025 pooled analysis of 7 trials (385 adults) found no significant fall in blood pressure or in C-reactive protein overall. A subgroup of trials lasting 8 weeks or more did show a CRP fall. Cholesterol and blood fats: Pooled trials found no effect of kefir on total, LDL or HDL cholesterol or triglycerides, and a small 2002 crossover trial of 13 men found the same versus milk. | 10 7 14 12 1 | |
| Inflammation Balance | Low certainty | Blood pressure and inflammation (CRP): A 2025 pooled analysis of 7 trials (385 adults) found no significant fall in blood pressure or in C-reactive protein overall. A subgroup of trials lasting 8 weeks or more did show a CRP fall. | 10 7 | |
| Cholesterol Balance | Low certainty | Cholesterol and blood fats: Pooled trials found no effect of kefir on total, LDL or HDL cholesterol or triglycerides, and a small 2002 crossover trial of 13 men found the same versus milk. | 14 12 1 7 | |
| Preventive Wellness | Low certainty | Mouth bacteria (Streptococcus mutans) and tooth decay: The 2023 review says kefir may have potential for lowering Streptococcus mutans in the mouth, a bacterium linked to tooth decay. No source read showed fewer cavities. | 7 | |
| Digestive Support | Low certainty | Diarrhea during antibiotics in young children: In a trial of 125 children aged 1 to 5 on antibiotics, kefir did not prevent diarrhea: 18% had it with kefir and 21.9% with placebo. | 9 | |
| Weight Management | Low certainty | Body weight and waist: In one 8-week trial of 75 overweight women, extra servings of kefir or of milk both led to more weight loss than the control diet, and kefir did no better than milk. | 3 14 | |
| Bone Health | Not enough evidence | Bone density and bone turnover: A small 2015 pilot trial in 40 people with osteoporosis reported short-term changes in bone markers and larger 6-month hip bone density gains with kefir plus calcium than with calcium alone. | 13 | |
| Better Sleep | Not enough evidence | Sleep and mental well-being: In the 2026 trial of 65 healthy young adults, sleep and mental health scores moved in a good direction but not significantly. | 1 | |
| Mood Balance | Not enough evidence | Sleep and mental well-being: In the 2026 trial of 65 healthy young adults, sleep and mental health scores moved in a good direction but not significantly. | 1 |
B. Body systems
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Musculoskeletal System | Biological association | High certainty | Studied for: Protein, calcium and vitamins (nutrient content) Studied for: Bone density and bone turnover | 21 13 |
| Digestive System | Biological association | Low certainty | Studied for: Lactose digestion and tolerance Studied for: Gut bacteria and gut comfort | 6 20 5 1 8 2 7 9 |
| Endocrine System | Biological association | Mixed findings | Studied for: Blood sugar and insulin resistance Studied for: Body weight and waist | 11 14 3 |
| Cardiovascular System | Biological association | Low certainty | Studied for: Blood pressure and inflammation (CRP) Studied for: Cholesterol and blood fats | 10 7 14 12 1 |
| Nervous System | Biological association | Not enough evidence | Studied for: Sleep and mental well-being | 1 |
E. Health conditions
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Cow's milk allergy | Adverse effect or risk | Documented risk | Kefir is a milk drink; milk is a major food allergen. Preparation or compound: Milk proteins in kefir |
15 18 |
| Weakened immune system | Adverse effect or risk | Documented risk (general to live culture products) | NCCIH: harm from probiotics is more likely in people with severe illness or weakened immunity. Kefir not named. NCCIH: harm from probiotics is greater in severe illness or weakened immunity. Kefir is not named. Preparation or compound: Live microbes in kefir |
17 4 |
| Listeriosis | Adverse effect or risk | Documented risk (unpasteurised dairy) | The NHS advises avoiding unpasteurised milk products in pregnancy. Preparation or compound: Unpasteurised dairy |
19 |
| Lactose intolerance | Preliminary | Plain kefir gave much less breath hydrogen than milk in 15 adults; kefir still contains lactose. Preparation or compound: Plain milk kefir |
6 20 | |
| Helicobacter pylori infection | Preliminary | Higher clearance as an add-on to triple therapy in one small trial; not a replacement. Preparation or compound: Milk kefir |
2 7 |
I. Biomarkers
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Breath hydrogen | Biological association | Low certainty | Measured in trials: lowered versus milk. A lab change is not the same as a health benefit. | 6 |
| Fasting insulin and HOMA-IR | Biological association | Mixed findings | Measured in trials: lowered. A lab change is not the same as a health benefit. | 14 11 |
| Blood pressure | Biological association | Low certainty | Measured in trials: no significant change. A lab change is not the same as a health benefit. | 10 |
| LDL cholesterol | Biological association | Low certainty | Measured in trials: no significant change. A lab change is not the same as a health benefit. | 14 12 |
| Body weight | Biological association | Low certainty | Measured in trials: no clear effect versus milk. A lab change is not the same as a health benefit. | 3 14 |
| Bone mineral density | Biological association | Not enough evidence | Measured in trials: reported higher at the hip. A lab change is not the same as a health benefit. | 13 |
K. Biological pathways
L. Active compounds
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Protein | Biological association | Human | Nutrient source. Preparation or compound: Milk |
21 |
| Lactose | Biological association | Human | Digested by the enzyme lactase; undigested lactose causes gas in lactose maldigestion. Preparation or compound: Milk |
21 6 |
| Calcium | Biological association | Human | Nutrient source; absorption from kefir was not researched. Preparation or compound: Milk |
21 |
| Live bacteria and yeasts | Biological association | Human | Kefir-specific bacterial species were found in stool in some trials, which the 2026 review takes to suggest colonisation. Counts depend on the product and whether it is heated after fermentation. Preparation or compound: Whole drink |
5 4 |
Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).
Evidence at a glance: what changed in 1 lab markers
Tap a number to show only those markers. Counts are markers, not people.
The evidence
The research centre for Kefir. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.
Evidence by outcome
Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).
How we rate evidence
High certainty
Several well-run trials or reviews agree; further research is unlikely to change the picture much.
Moderate certainty
Good trials point the same way, but some doubt remains.
Low certainty
Small, short or inconsistent trials. The finding could change with better research.
Very low certainty
Very little or very weak human data. Treat as a possibility only.
Mixed findings
Trials or reviews disagree with each other.
Not enough evidence
Not enough human research to say either way.
Evidence against
Good research found no benefit, or found harm.
We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We started from our existing kefir summary, re-checked nutrition against saved USDA FoodData Central data, read health agency pages (NCCIH, FDA, NHS, MedlinePlus, NIDDK) and re-read PubMed abstracts for reviews and trials. Only abstracts were read for studies. Items we could not verify are flagged in the research gaps.
Study library: every study we checked 21
| Study | Design | People | Product, dose, length | Result |
|---|---|---|---|---|
| Bakirhan 2026 Effects of Kefir Consumption on Gastrointestinal Health, Biochemical Parameters, Sleep, and Mental Well-Being in Healthy Young Adults: a Randomized Controlled Trial. J Nutr · PMID 41314291 · DOI |
Randomised controlled trial |
65 65 healthy young adult volunteers |
Lactose-free kefir, 250 mL a day Milk kefir as a drink 250 mL a day 6 weeks · vs Not described in the abstract |
Gut symptoms decreased, and serum cholesterol, creatinine and uric acid fell after kefir (P<0.05). Immunity and inflammation markers did not improve significantly. Glucose, CRP, sleep and mental health scores moved in a good direction but not significantly. Some body measures rose. No numbers in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: Gut symptoms, blood tests, sleep, mental health, immunity, inflammation Limitations: The product was lactose-free kefir. Healthy, young, small sample. The abstract does not say what the comparison group received. Many outcomes were tested. Funding and conflicts: The authors declare no commercial or financial conflicts. Registered NCT06612164. Read: abstract |
| Bekar 2011 Kefir improves the efficacy and tolerability of triple therapy in eradicating Helicobacter pylori. J Med Food · PMID 21186984 · DOI |
Randomised double blind trial |
82 82 patients with dyspepsia and H. pylori infection confirmed by urea breath test |
Kefir 250 mL twice daily with 14 days of standard triple therapy (lansoprazole, amoxicillin, clarithromycin) Milk kefir as a drink 250 mL twice daily 14 days of treatment; breath test at 45 days · vs Triple therapy plus 250 mL milk containing placebo |
Eradication: 36 of 46 (78.2%) with kefir versus 18 of 36 (50.0%) with placebo. Side effects were less frequent and less severe with kefir. Eradication 78.2% vs 50.0% (P = .026) Methods, limits and fundingOutcomes: H. pylori eradication; side effects by questionnaire Limitations: One small trial in one setting. Unequal group sizes (46 and 36). Kefir was an add-on to medicine, not a replacement. Funding not stated in the abstract. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Fathi 2016 Kefir drink leads to a similar weight loss, compared with milk, in a dairy-rich non-energy-restricted diet in overweight or obese premenopausal women: a randomized controlled trial. Eur J Nutr · PMID 25648739 · DOI |
Randomised controlled trial |
75 75 overweight or obese premenopausal women aged 25 to 45 (58 finished) |
Commercial kefir drink, 2 extra servings a day within a dairy-rich diet Milk kefir as a drink 2 extra dairy servings a day 8 weeks · vs Low-fat milk (2 extra servings) and a control group (2 servings of low-fat dairy a day in total) |
Kefir and milk groups lost more weight, BMI and waist than the control group (all p<0.01). Kefir and milk did not differ from each other. Kefir versus milk: no significant difference (Not given in the abstract) Methods, limits and fundingOutcomes: Weight, BMI, waist circumference Limitations: Only 58 of 75 finished (analysis was intention-to-treat). Eight weeks. The result is about dairy servings, not kefir specifically. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Gupta 2024 Safety, feasibility, and impact on the gut microbiome of kefir administration in critically ill adults. BMC Med · PMID 38378568 · DOI |
Open label safety study |
54 54 critically ill adults in intensive care with an intact gut |
Kefir in rising amounts (60 mL, then 120 mL after 12 h, then 240 mL daily) Milk kefir as a drink 60 to 240 mL, as described in the abstract Daily during the ICU stay |
None of the 54 had signs of kefir-related bacteremia. No bloating, vomiting or aspiration, except diarrhea in two patients also taking laxatives. 359 of 393 doses (91%) were given. Gut diversity did not increase. A gut wellness index rose (P = 0.034, one-sided test), and kefir microbes engrafted to varying degrees. 0 of 54 with kefir-related bacteremia (Not applicable) Methods, limits and fundingOutcomes: Safety (gut symptoms, bacteria in the blood), feasibility, gut microbiome in 13 patients Limitations: Open-label safety study done in hospital with monitoring, with no comparison group. It cannot be taken as proof of safety at home. Paired stool samples came from only 13 patients. Funding and conflicts: The authors declare no competing interests. Registered NCT05416814. Read: abstract |
| Hamsho 2026 Kefir: A Potential Gut Microbiota Modulator: A Systematic Review of Human Interventional Studies. Microbiologyopen · PMID 42036973 · DOI |
Systematic review |
8 human intervention studies (from 2,743 records) | Kefir by mouth Milk kefir as a drink Varied Varied · vs Varied |
Kefir gave minor changes at phylum and class level. Bifidobacterium increased in 3 of 4 studies. Kefir-specific bacteria were found in stool, which the authors take to suggest colonisation. Overall changes were modest and varied. Direct functional evidence in people is limited. No pooled number in the abstract (Not applicable) Methods, limits and fundingOutcomes: Gut microbiota composition Limitations: Eight studies of mixed design. A change in gut bacteria is not a health outcome. Funding and conflicts: The authors declare no conflicts of interest. Read: abstract |
| Hertzler 2003 Kefir improves lactose digestion and tolerance in adults with lactose maldigestion. J Am Diet Assoc · PMID 12728216 · DOI |
Randomised crossover trial |
15 15 healthy adults with lactose maldigestion |
Plain and raspberry kefir (compared with 2% milk and plain and raspberry yogurt), each test meal with 20 g lactose Milk kefir as a drink One test meal each 8-hour monitoring after each meal · vs 2% milk, yogurt |
Breath hydrogen was much higher after milk than after plain kefir or plain yogurt. Flavoured kefir was in between. Yogurts and kefirs cut the perceived severity of flatulence by 54 to 71% compared with milk. Abdominal pain and diarrhea were negligible with all five test meals. Breath hydrogen AUC: milk 224 +/- 39 ppm x h; plain kefir 87 +/- 37; plain yogurt 76 +/- 14; flavoured kefir 156 +/- 26 (P<.001 for milk versus plain kefir) Methods, limits and fundingOutcomes: Breath hydrogen (a sign of undigested lactose reaching the gut) and symptoms, hourly for 8 hours Limitations: 15 people, single test meals, 2003. Not a long-term trial. Funding not stated in the abstract. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Kairey 2023 The effects of kefir consumption on human health: a systematic review of randomized controlled trials. Nutr Rev · PMID 35913411 · DOI |
Systematic review |
18 publications reporting 16 randomised trials of fermented-milk kefir in people (searched to July 2021) | Fermented-milk kefir by mouth Milk kefir as a drink Varied Varied · vs Varied (not summarised in the abstract) |
Narrative analysis: kefir may have potential as an add-on for lowering oral Streptococcus mutans (a tooth-decay bacterium) and in Helicobacter pylori eradication therapy. It may further aid treatment of adult dyslipidemia and hypertension, but evidence was very limited. Safety was assessed in only 5 of 18 publications. 12 studies had an overall high risk of bias. The authors call kefir apparently safe for generally healthy people, and say high-quality trials are needed before any recommendation. Narrative; no pooled number in the abstract (Not applicable) Methods, limits and fundingOutcomes: Any human health outcome Limitations: Abstract only; trial-level details and the dental and cholesterol trials were not read. Registered on PROSPERO (CRD42020211494). Funding and conflicts: No funding or conflict statement appears in the abstract or record read. Read: abstract |
| Marco 2021 The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nat Rev Gastroenterol Hepatol · PMID 33398112 · DOI |
Expert consensus statement n/a |
Expert panel convened September 2019 | Fermented foods in general Milk kefir as a drink |
Defines fermented foods as foods made through desired microbial growth and enzymatic conversions of food components, clarifies that fermented foods are not the same as probiotics, and reviews safety, nutrition and possible mechanisms. Kefir is not singled out in the abstract. Not applicable (Not applicable) Methods, limits and fundingOutcomes: Definition of fermented foods, and their safety, risks and health benefits Limitations: A consensus statement, not a trial. Abstract only. Funding and conflicts: Several authors report paid work for food, dairy and probiotic companies (for example Danone, Yakult, Kerry, Associated British Foods). Flagged as industry-linked. Read: abstract |
| Merenstein 2009 A randomized clinical trial measuring the influence of kefir on antibiotic-associated diarrhea: the measuring the influence of Kefir (MILK) Study. Arch Pediatr Adolesc Med · PMID 19652108 · DOI |
Randomised placebo controlled trial |
125 125 children aged 1 to 5 years given antibiotics, US primary care |
Commercial kefir drink (versus heat-killed matching placebo) Milk kefir as a drink 14-day follow-up · vs Heat-killed placebo |
No difference: diarrhea in 18% on kefir and 21.9% on placebo. No differences in secondary outcomes. The authors said kefir did not prevent antibiotic-associated diarrhea. Diarrhea 18% vs 21.9% (relative risk 0.82) (95% CI 0.54 to 1.43) Methods, limits and fundingOutcomes: Diarrhea during the 14 days of antibiotics Limitations: Young children only. The authors noted interactions with initial health, age and sex that need study. Funding not stated in the abstract. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Rashidbeygi 2025 The Effect of Kefir Consumption on Blood Pressure and C-Reactive Protein: A Systematic Review and Meta-Analysis of Randomised Controlled Trials. Endocrinol Diabetes Metab · PMID 41139305 · DOI |
Systematic review meta analysis |
385 7 randomised trials in adults, 385 people (searched to January 2025) |
Kefir drink Milk kefir as a drink Varied At least 2 weeks · vs Control groups (not described in the abstract) |
No significant effect on systolic blood pressure, diastolic blood pressure or CRP overall. A subgroup of trials lasting 8 weeks or more showed a significant CRP fall. Systolic BP WMD -1.76 mmHg; diastolic BP WMD -1.19 mmHg; CRP WMD -0.17 mg/L (Systolic -5.21 to 1.69 (p 0.317); diastolic -3.40 to 1.03 (p 0.295); CRP -0.84 to 0.49 (p 0.609)) Methods, limits and fundingOutcomes: Systolic and diastolic blood pressure; C-reactive protein (CRP, an inflammation marker) Limitations: Few small trials. The subgroup finding is exploratory. Funding and conflicts: The authors declare no conflicts of interest. Read: abstract |
| Salari 2021 Effect of kefir beverage consumption on glycemic control: A systematic review and meta-analysis of randomized controlled clinical trials. Complement Ther Clin Pract · PMID 34280689 · DOI |
Systematic review meta analysis |
323 6 randomised trials, 323 people (searched to July 2020) |
Kefir beverage Milk kefir as a drink Varied (the authors note varied dose and duration) Varied · vs Control groups (not described in the abstract) |
Fasting blood sugar and insulin were lower in the kefir groups. HbA1c was not significantly lower. FBS WMD -10.28 (units not given in the abstract); insulin WMD -2.87; HbA1c WMD -0.64 (FBS -16.53 to -4.02 (p 0.001); insulin -3.96 to -1.78 (p<0.00001); HbA1c -1.36 to 0.08 (p 0.08)) Methods, limits and fundingOutcomes: Fasting blood sugar (FBS), HbA1c, insulin Limitations: Few small trials with varied dose and length. The abstract says changes were compared to baseline. A 2023 meta-analysis of 6 trials found no fasting blood sugar effect, so results disagree. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| St-Onge 2002 Kefir consumption does not alter plasma lipid levels or cholesterol fractional synthesis rates relative to milk in hyperlipidemic men: a randomized controlled trial [ISRCTN10820810]. BMC Complement Altern Med · PMID 11825344 · DOI |
Randomised crossover trial |
13 13 men with mildly raised cholesterol |
Kefir as a dairy supplement (compared with milk) Milk kefir as a drink As described in the study (not given in the abstract) Two 4-week periods · vs Milk |
Kefir had no effect on total, LDL or HDL cholesterol, triglycerides or cholesterol synthesis after 4 weeks. Both kefir and milk raised some fecal short-chain fatty acids. The authors said the results do not support kefir as a cholesterol-lowering agent. No difference versus milk (Not given in the abstract) Methods, limits and fundingOutcomes: Total, LDL and HDL cholesterol, triglycerides, cholesterol synthesis rate, fecal short-chain fatty acids Limitations: Only 13 men, 4 weeks, 2002. Funding not stated in the abstract. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Tu 2015 Short-Term Effects of Kefir-Fermented Milk Consumption on Bone Mineral Density and Bone Metabolism in a Randomized Clinical Trial of Osteoporotic Patients. PLoS One · PMID 26655888 · DOI |
Randomised double blind pilot trial |
40 40 people with osteoporosis |
Kefir-fermented milk (1,600 mg, as described in the abstract) plus calcium carbonate 1,500 mg Milk kefir as a drink As described in the abstract 6 months · vs Calcium carbonate alone |
The authors report that kefir was associated with short-term changes in bone turnover and greater 6-month increases in hip bone density. Some marker changes were seen only in subgroups (for example people with T-scores above -1). Parathyroid hormone rose with kefir and fell in the control group. No group means in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: Bone turnover markers at 1, 3 and 6 months; bone mineral density at baseline and 6 months Limitations: Pilot study of 40 people. The abstract gives no between-group numbers, and the kefir group also got calcium. Registered NCT02361372. Funding and conflicts: The authors declare no competing interests. Read: abstract |
| Yahyapoor 2023 Effects of Kefir Consumption on Cardiometabolic Risk Factors: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Curr Drug Targets · PMID 37102491 · DOI |
Systematic review meta analysis |
314 6 randomised trials, 314 people (searched to June 2021) |
Kefir beverage Milk kefir as a drink Varied Varied · vs Control groups (not described in the abstract) |
Fasting insulin and HOMA-IR fell. No effect on total cholesterol, triglycerides, HDL, LDL, fasting blood sugar, HbA1c or body weight. Insulin WMD -3.69 micro-IU/mL; HOMA-IR WMD -2.56 (Insulin -6.30 to -1.07 (p 0.006); HOMA-IR -3.82 to -1.30 (p<0.001); LDL p 0.910; total cholesterol p 0.088; fasting blood sugar p 0.267) Methods, limits and fundingOutcomes: Insulin, HOMA-IR (insulin resistance), total, LDL and HDL cholesterol, triglycerides, fasting blood sugar, HbA1c, body weight Limitations: Few small trials. Differences from the 2021 glycemic meta-analysis (which found lower fasting blood sugar) are not explained in the abstracts. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| s-fda-allergens US FDA: Food Allergies · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-medlineplus-foodallergy MedlinePlus: Food allergy · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nccih-probiotics NCCIH: Probiotics: Usefulness and Safety · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nhs-food-allergy NHS: Food allergy · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nhs-foods-to-avoid NHS: Foods to avoid in pregnancy · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-niddk-lactose NIDDK: Eating, Diet, & Nutrition for Lactose Intolerance · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-usda-fdc-170904 USDA FoodData Central: Kefir, lowfat, plain, LIFEWAY (FDC 170904, SR Legacy, April 2018) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text |
What we do not know yet
- The trials behind the 2023 review's dental, blood pressure and cholesterol statements were not read; only abstracts were read throughout.
- No long-term trial of kefir for gut symptoms or lactose tolerance was found.
- The two blood sugar analyses overlap and disagree; the reason was not checked.
- Tyramine and MAOI antidepressants, alcohol content, histamine, FODMAP, pasteurisation of retail kefir, breastfeeding and infants were not researched.
- USDA values are for one branded plain lowfat product.
How new research is added
New studies are found by a saved PubMed search and placed in a review queue before the page changes.
Lab markers
What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".
Metabolic 2
LDL cholesterol
No significant change in trials
The 'bad' cholesterol carried in the blood.
Low certaintyResults and what it means
Why it was measured
The usual blood marker in diet trials for heart risk.
Statistical vs. clinical meaning
No clear effect.
Safety implication
None specific.
Body weight
No clear effect versus milk in trials
Weight on the scale.
Low certaintyResults and what it means
Why it was measured
A basic diet-trial outcome.
Statistical vs. clinical meaning
No kefir-specific effect.
Safety implication
None specific.
Other 4
Breath hydrogen
Lowered versus milk in trials
A gas on the breath that rises when lactose is not digested and reaches gut bacteria.
Low certaintyResults and what it means
Why it was measured
To see how well lactose was digested.
Statistical vs. clinical meaning
Small, single-meal result.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 6 | Breath hydrogen AUC 87 ppm x h with plain kefir versus 224 with milk (P<.001) | 15 adults with lactose maldigestion | 20 g lactose in plain kefir versus milk |
Fasting insulin and HOMA-IR
Lowered in trials
Insulin level after fasting, and an index of how well the body responds to insulin.
Mixed findingsResults and what it means
Why it was measured
Used in diet trials as a sign of insulin resistance.
Statistical vs. clinical meaning
Insulin fell in both analyses; fasting blood sugar differed between them.
Safety implication
None specific.
Blood pressure
No significant change in trials
The force of blood on artery walls.
Low certaintyResults and what it means
Bone mineral density
Reported higher at the hip in trials
How dense the bones are on a DXA scan.
Not enough evidenceResults and what it means
Why it was measured
The usual measure of osteoporosis.
Statistical vs. clinical meaning
Pilot only.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 13 | The authors report greater 6-month hip bone density increases with kefir plus calcium; no numbers in the abstract | 40 people with osteoporosis | Kefir-fermented milk plus calcium carbonate versus calcium alone |
Safety
What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.
Main points to know 4
- Kefir is a milk product: not safe for cow's milk allergy. The US FDA lists milk among the nine major food allergens, and MedlinePlus and the NHS list cow's milk among the most common causes of food allergy. Kefir is made from milk, so people with a milk allergy should avoid it unless an allergist says otherwise. None of the pages read names kefir, and whether fermentation changes this was not researched. Authoritative guidance 15 16 18
- Weakened immune system or serious illness. NCCIH says the risk of harm from probiotics is greater in people with severe illness or weakened immune systems, and that severe or fatal infections have been reported in premature infants given probiotics. NCCIH does not name kefir. In one open-label hospital study of 54 critically ill adults, none had signs of kefir-related bacteremia. That was done with monitoring and is not proof of safety at home. Ask your care team first. Authoritative guidance and open label study 17 4
- Unpasteurised milk products in pregnancy. The NHS says to avoid unpasteurised milk, cream, yoghurt, butter and ice cream in pregnancy because they may carry listeria, which can cause miscarriage or stillbirth or make a newborn very unwell. It says pasteurised milk and yoghurt are safe. It does not name kefir, and no source read said how kefir is pasteurised. Check the label. Authoritative guidance 19
- Breastfeeding, infants and young children. Breastfeeding was not researched (LactMed was not searched). One trial gave kefir to 125 children aged 1 to 5 and found no benefit against antibiotic diarrhea; its abstract gives no safety detail. No source read gave advice for infants. Ask a pediatrician or your doctor. Gap 9
Side effects 4
| Effect | How often | Severity and recovery | Evidence |
|---|---|---|---|
| Allergic reaction to milk protein, from hives and swelling to anaphylaxis The sources describe milk allergy in general, not kefir. | No kefir-specific frequency found. | can be severe Not described in the sources read. | Authoritative guidance 15 18 |
| Gas, bloating or loose stools in people sensitive to lactose Lactose intolerance is not an allergy. Kefir still contains lactose, and the trial had 15 people. | In the 2003 trial, flatulence was lower after kefir than after milk, and abdominal pain and diarrhea were negligible. USDA lists 3.7 g of lactose per 100 g for one plain lowfat kefir. | mild Not described. | Randomised trial and database 6 21 20 16 |
| Diarrhea in a small number of hospital patients on laxatives Both were also taking laxatives. No bloating, vomiting or aspiration was seen. | 2 of 54 critically ill adults | mild Not described. | Open label study 4 |
| Side effects in controlled trials were rarely reported Little safety reporting means a gap in knowledge, not proof of safety. | Safety was assessed in only 5 of 18 publications in the 2023 review. | unclear Not applicable | Systematic review 7 |
Liver
No liver injury from kefir was found in the sources read. No liver-safety database was searched for kefir.
How often. Not found.
Monitoring. No agency monitoring advice was found.
This is a safety connection. It is not evidence that Kefir supports liver health.
Medicines and supplements 3
| With | Why it matters | Importance | Evidence | What to do |
|---|---|---|---|---|
| Medicines that weaken the immune system (for example after a transplant or during chemotherapy) prescription | NCCIH says the risk of harm from probiotics is greater in people with weakened immune systems. Kefir is a live-culture food but is not named. | No kefir-specific interaction report was found. | Authoritative guidance Low certainty 17 | Ask your care team before using live-culture foods if your immune system is weakened. |
| Standard H. pylori triple therapy (lansoprazole, amoxicillin, clarithromycin) prescription | Kefir was given alongside these medicines in one trial and side effects were fewer. | No harmful interaction was reported in that trial's abstract. | Randomised trial Low certainty 2 | Do not stop prescribed treatment. Ask your prescriber before adding anything. |
| MAOI antidepressants (tyramine in fermented foods) prescription | Some aged or fermented foods can contain tyramine. | No source read reported tyramine levels or a problem for kefir. This was not researched. | Not researched Not enough evidence | If you take an MAOI, ask your prescriber or pharmacist about fermented dairy. |
Who should check first 2
| Situation | Advice | Evidence |
|---|---|---|
| Cow's milk allergy | Avoid unless an allergist says otherwise. For trouble breathing or swelling of the face, lips or throat, call your local emergency number. | Authoritative guidance 15 18 16 |
| Severe illness or a weakened immune system | Ask your care team before using live-culture foods. | Authoritative guidance 17 |
Overdose, product quality and regulators
Summary. No toxicity from kefir as an ordinary food was found in the sources read. The safety points are allergy, lactose, live microbes in weakened immunity, and unpasteurised dairy in pregnancy.
Animal. Not reviewed.
Overdose response. Not found.
Genotoxicity. Not researched.
Spoilage, listeria, mould, yeast overgrowth and alcohol content of kefir were not studied in the sources read, except for unpasteurised dairy in general.
Unpasteurised dairy. The NHS says unpasteurised milk, yoghurt and cream may contain listeria. Whether a given kefir used pasteurised milk is something to check on the label. 19
Alcohol from fermentation. A 2021 meta-analysis describes kefir as made by lactic-alcoholic fermentation, so it can contain some alcohol. The amount was not measured in any source read. 11
Live microbes not listed on a label. NCCIH says some probiotic products have been reported to contain microorganisms other than those on the label. This is about probiotic products in general, not kefir. 17
| Body | Action | Date |
|---|---|---|
| US FDA (United States) | Food Allergies: milk is one of nine major food allergens. source | 2026-03-11 |
| NCCIH (US National Institutes of Health) (United States) | Probiotics: Usefulness and Safety. Risk of harm greater in people with severe illness or weakened immunity; severe infections reported in premature infants. source | 2019-08 |
| NHS (UK) (United Kingdom) | Foods to avoid in pregnancy: unpasteurised milk, cream, yoghurt, butter and ice cream; pasteurised milk and yoghurt are safe. source | 2026-06-15 |
| No kefir-specific statement (n/a) | No regulator statement naming kefir was found in the pages read (FDA, NCCIH, NHS, NIDDK, MedlinePlus). |
When to get medical help
- Trouble breathing, wheezing, swelling of the lips, face, tongue or throat, widespread hives or fainting after drinking kefir: call your local emergency number.
- Fever, chills or feeling very unwell after eating kefir if you are pregnant, have a weakened immune system or are seriously ill: seek urgent medical care.
- Bloody diarrhea, severe belly pain or a fever that does not settle: seek medical care.
Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.
General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.
Frequently asked questions
What is kefir?
What nutrients are in kefir?
By USDA data for one plain lowfat product, 100 g has 3.79 g of protein, 130 mg of calcium, 0.135 mg of riboflavin and 0.29 ug of vitamin B12. A cup (243 g) has about 104 kcal and 11.2 g of sugars, most of it milk sugar. Brands, fat levels and added sugar differ, so check the label.
Is kefir a probiotic?
Can I drink kefir if I am lactose intolerant?
Is kefir safe for a cow's milk allergy?
Does kefir help the gut?
Does kefir lower blood pressure or cholesterol?
Does kefir help with blood sugar?
Can kefir help with H. pylori?
Does kefir prevent diarrhea from antibiotics?
A trial of 125 children aged 1 to 5 found no difference: diarrhea in 18% on kefir and 21.9% on placebo. Ask a doctor before giving kefir to a young child with diarrhea.
Is kefir safe in pregnancy or with a weak immune system?
Does kefir contain alcohol?
It can contain a little. A 2021 analysis describes kefir as made by lactic-alcoholic fermentation, but no source we read measured the amount.
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Editorial transparency
- Written by
- AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
- Medical review
- None. This page has not been reviewed by a physician or pharmacist.
- First published
- 2026-10-26
- Last substantive update
- 2026-10-26
- How we research
- We started from our existing kefir summary, re-checked nutrition against saved USDA FoodData Central data, read health agency pages (NCCIH, FDA, NHS, MedlinePlus, NIDDK) and re-read PubMed abstracts for reviews and trials. Only abstracts were read for studies. Items we could not verify are flagged in the research gaps.
- How we rate evidence
- See "How we rate evidence" in the Evidence tab.
- Independence
- No product is promoted on this page. No affiliate links are shown. The trials' funding is mostly not stated in the abstracts. Several authors of the ISAPP consensus statement report paid work for dairy, food and probiotic companies; this is stated where it is used.
Sources 21
Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.
- Bakirhan H, Ozyurek Arpa F, Pehlivan M, Kalkan I. Effects of Kefir Consumption on Gastrointestinal Health, Biochemical Parameters, Sleep, and Mental Well-Being in Healthy Young Adults: a Randomized Controlled Trial.. J Nutr. 2026. PMID 41314291. DOI 10.1016/j.tjnut.2025.11.016. (abstract)
- Bekar O, Yilmaz Y, Gulten M. Kefir improves the efficacy and tolerability of triple therapy in eradicating Helicobacter pylori.. J Med Food. 2011. PMID 21186984. DOI 10.1089/jmf.2010.0099. (abstract)
- Fathi Y, Faghih S, Zibaeenezhad MJ, Tabatabaei SH. Kefir drink leads to a similar weight loss, compared with milk, in a dairy-rich non-energy-restricted diet in overweight or obese premenopausal women: a randomized controlled trial.. Eur J Nutr. 2016. PMID 25648739. DOI 10.1007/s00394-015-0846-9. (abstract)
- Gupta VK, Rajendraprasad S, Ozkan M, Ramachandran D. Safety, feasibility, and impact on the gut microbiome of kefir administration in critically ill adults.. BMC Med. 2024. PMID 38378568. DOI 10.1186/s12916-024-03299-x. (abstract)
- Hamsho M, Ranneh Y, Kaddour B, Alfakhri S. Kefir: A Potential Gut Microbiota Modulator: A Systematic Review of Human Interventional Studies.. Microbiologyopen. 2026. PMID 42036973. DOI 10.1002/mbo3.70297. (abstract)
- Hertzler SR, Clancy SM. Kefir improves lactose digestion and tolerance in adults with lactose maldigestion.. J Am Diet Assoc. 2003. PMID 12728216. DOI 10.1053/jada.2003.50111. (abstract)
- Kairey L, Leech B, El-Assaad F, Bugarcic A. The effects of kefir consumption on human health: a systematic review of randomized controlled trials.. Nutr Rev. 2023. PMID 35913411. DOI 10.1093/nutrit/nuac054. (abstract)
- Marco ML, Sanders ME, Gaenzle M, Arrieta MC, et al.. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods.. Nat Rev Gastroenterol Hepatol. 2021. PMID 33398112. DOI 10.1038/s41575-020-00390-5. (abstract)
- Merenstein DJ, Foster J, D'Amico F. A randomized clinical trial measuring the influence of kefir on antibiotic-associated diarrhea: the measuring the influence of Kefir (MILK) Study.. Arch Pediatr Adolesc Med. 2009. PMID 19652108. DOI 10.1001/archpediatrics.2009.119. (abstract)
- Rashidbeygi E, Samarin MM, Sheikhhossein F, Khalilkhaneh AH. The Effect of Kefir Consumption on Blood Pressure and C-Reactive Protein: A Systematic Review and Meta-Analysis of Randomised Controlled Trials.. Endocrinol Diabetes Metab. 2025. PMID 41139305. DOI 10.1002/edm2.70124. (abstract)
- Salari A, Ghodrat S, Gheflati A, Jarahi L. Effect of kefir beverage consumption on glycemic control: A systematic review and meta-analysis of randomized controlled clinical trials.. Complement Ther Clin Pract. 2021. PMID 34280689. DOI 10.1016/j.ctcp.2021.101443. (abstract)
- St-Onge MP, Farnworth ER, Savard T, Chabot D. Kefir consumption does not alter plasma lipid levels or cholesterol fractional synthesis rates relative to milk in hyperlipidemic men: a randomized controlled trial [ISRCTN10820810].. BMC Complement Altern Med. 2002. PMID 11825344. DOI 10.1186/1472-6882-2-1. (abstract)
- Tu MY, Chen HL, Tung YT, Kao CC. Short-Term Effects of Kefir-Fermented Milk Consumption on Bone Mineral Density and Bone Metabolism in a Randomized Clinical Trial of Osteoporotic Patients.. PLoS One. 2015. PMID 26655888. DOI 10.1371/journal.pone.0144231. (abstract)
- Yahyapoor F, Haghighat N, Sohrabi Z, Asbaghi O. Effects of Kefir Consumption on Cardiometabolic Risk Factors: A Systematic Review and Meta-analysis of Randomized Controlled Trials.. Curr Drug Targets. 2023. PMID 37102491. DOI 10.2174/1389450124666230427095742. (abstract)
- . US FDA: Food Allergies. . . (full-text)
- . MedlinePlus: Food allergy. . . (full-text)
- . NCCIH: Probiotics: Usefulness and Safety. . . (full-text)
- . NHS: Food allergy. . . (full-text)
- . NHS: Foods to avoid in pregnancy. . . (full-text)
- . NIDDK: Eating, Diet, & Nutrition for Lactose Intolerance. . . (full-text)
- . USDA FoodData Central: Kefir, lowfat, plain, LIFEWAY (FDC 170904, SR Legacy, April 2018). . . (full-text)
