How we rate
“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
Kefir
Fermented milk: slightly lower fasting blood glucose and insulin in meta-analyses; on cholesterol, weight and blood pressure, no better than milk.
Benefits
- Fasting blood glucose: −8.46 mg/dL on average in a meta-analysis of 24 intervention studies, −10.28 in another of 6 trials and 323 participants.
- Insulin: the insulin resistance index (HOMA-IR) drops by 1.71 in one meta-analysis and by 2.56 in another; fasting insulin by 2.87 and 3.69.
- Lactose: in 15 adults who digest lactose poorly, plain kefir dropped expired hydrogen from 224 to 87 ppm·h compared to milk; yogurts and kefirs reduced gas discomfort by 54 to 71%.
- Type 2 diabetes: in 60 patients, 600 mL per day of a probiotic fermented milk for 8 weeks lowered HbA1c more than a conventional fermented milk.
- LDL cholesterol: in 21 men with high LDL, 2 servings (350 g) per day of kefir made with traditional microorganisms for 4 weeks lowered LDL and markers of inflammation.
- Constipation: in 20 patients, 500 mL per day for 4 weeks made stools more frequent and less hard, and reduced laxatives; pilot study without a control group.
Precautions
Lactose: kefir still contains some; in adults who digest it poorly, it was better tolerated than milk, but flavored kefir was less well tolerated than plain (156 vs. 87 ppm·h). Safety: a review of 16 trials considers it safe in healthy people, but only 5 out of 18 publications had measured adverse effects. Limitations: compared to milk: in 75 overweight women, 2 extra servings per day of kefir or milk lowered cholesterol (LDL −9.7 mg/dL with kefir) and weight just as much; no difference between the two. Cholesterol: in 13 men with slightly high cholesterol, 4 weeks of kefir changed neither LDL nor triglycerides; a meta-analysis of 6 trials finds no effect on lipids or weight. Blood pressure: a meta-analysis of 7 trials and 385 adults finds no significant drop (−1.76 mmHg systolic), nor in CRP on average. HbA1c: no significant drop in meta-analyses (−0.64, p = 0.08). Fatty liver: in 80 patients, 500 mL per day for 8 weeks in addition to a diet changed neither liver enzymes, nor weight, nor depression compared to diet alone. Antibiotics: in 125 children aged 1 to 5, kefir did not prevent antibiotic-associated diarrhea (18% vs. 21.9% on placebo). Quality of evidence: 12 of the 16 trials in a systematic review had a high risk of bias, and some tested "kefirs" were probiotic fermented milks without kefir grains.
Recommended dosage
180 to 600 mL per day in trials, for 3 to 12 weeks.
How to take it
- For whom: most trials involve sick or overweight people (diabetes, metabolic syndrome, fatty liver, constipation); very few involve athletes.
- Dose: from 180 mL per day (metabolic syndrome) to 500 mL (constipation, fatty liver) and 600 mL (type 2 diabetes).
- Duration: 3 to 12 weeks in trials; CRP, a marker of inflammation, only dropped after 8 weeks.
- Which kefir: in a crossover trial, only kefir made with traditional microorganisms lowered LDL; the commercial kefir tested, which did not contain them, increased TNF-α.
- Sport: in 11 "masters" endurance athletes, 14 days of kefir did not improve a 5 km time trial (33 min 41 vs. 33 min 39 with water), but reduced digestive issues after an exhausting effort.
- Timing: no study in this sheet compares morning, evening, or taking it with a meal.
Did you know?
In 21 men with high LDL cholesterol, a kefir made with traditional microorganisms lowered LDL, whereas a commercial kefir that did not contain any increased a marker of inflammation (TNF-α).
What the studies say
This meta-analysis examined the effects of kefir consumption on several health indicators in adults. It concluded that kefir consumption led to a significant reduction in fasting blood glucose and insulin resistance (HOMA-IR). However, no significant effect was found on anthropometric measurements, lipid profile, or inflammatory markers.
Hamsho M, Hawari R, Yeşil Z, Dakhel Z, Dursun Saydam D, Terzi M, Ranneh Y. — Nutrition, metabolism, and cardiovascular diseases : NMCD (2026) — View the source study
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more