Kefir
By Superfoods Advisor Editors·July 3, 2026
Kefir vs yogurt: how the fermented milk drink differs in microbes, protein and calcium, and what human studies show about kefir benefits and side effects.
Kefir (also spelled kephir or kefyr) is a fermented milk drink made by culturing milk with kefir grains, a symbiotic community of lactic acid bacteria and yeasts. Compared with yogurt, which is set with two bacterial species, kefir is thinner, slightly fizzy, and carries a wider mix of microbes, including yeasts.
The drink originated in the Caucasus Mountains (Rosa et al., 2017), and the name likely derives from the Turkish keyif, “good feeling.” Traditional kefir is made by adding grains (cauliflower-shaped clusters of polysaccharides, proteins and microbes) to cow, goat, or sheep milk. The milk ferments at room temperature (one standard method uses 18–24 °C for about 18 hours; Farag et al., 2020), and the grains are strained out and reused. The result is mildly tart and effervescent from yeast-produced carbon dioxide.
The fermentation process substantially alters the nutritional composition of the original milk. Part of the lactose is consumed as microbial lactase enzymes break it down to glucose and galactose, and the lower-lactose result was tolerated better than milk by adults with lactose maldigestion in a small trial (Hertzler & Clancy, 2003). Proteins are partially hydrolyzed into bioactive peptides, and the microbial activity generates short-chain fatty acids, B vitamins, and vitamin K2.
Evidence at a glance
Microbial Profile and Active Compounds
Kefir grains harbor a diverse and relatively stable microbial ecosystem. Bacterial members typically include lactic acid bacteria (LAB) such as Lactobacillus kefiranofaciens, Lactobacillus kefiri, Lactobacillus acidophilus, Leuconostoc mesenteroides, and Lactococcus lactis. Acetic acid bacteria (Acetobacter spp.) are also commonly present. Yeasts — including Saccharomyces cerevisiae, Kluyveromyces marxianus, and Kazachstania unispora — contribute to the characteristic effervescence and produce antimicrobial compounds such as ethanol (typically around 0.5%, with about 0.3–1% reported depending on how much grain is used; Farag et al., 2020).
Lactobacilli alone have been counted at roughly 10⁸–10⁹ colony-forming units per milliliter (CFU/mL) in grain-fermented kefir (Farag et al., 2020), so a 200 mL serving can supply on the order of 10¹⁰ CFU or more. Commercial products often contain fewer: in one analysis of five US kefirs, most products with a guaranteed count overstated it by at least tenfold, and only one exceeded 10⁹ CFU/g (Metras et al., 2021). Lactobacillus kefiranofaciens produces the exopolysaccharide kefiran, which has been investigated independently for immunomodulatory and antimicrobial properties.
Fermentation also generates bioactive peptides released from casein and whey proteins, some of which show ACE-inhibitory and antimicrobial activity in laboratory studies (Bourrie et al., 2016).
Nutritional Profile
Plain low-fat kefir is a low-calorie source of protein, calcium, vitamin B12 and riboflavin, at 43 kcal per 100 g. Values per 100 g of plain, low-fat kefir (USDA FoodData Central):
| Nutrient | Amount | % DV |
|---|---|---|
| Energy | 43 kcal | — |
| Protein | 3.8 g | — |
| Total fat | 1.0 g | — |
| Carbohydrates | 4.8 g | — |
| Calcium | 130 mg | 10% |
| Phosphorus | 105 mg | — |
| Vitamin B12 | 0.29 µg | 12% |
| Riboflavin (B2) | 0.14 mg | 10% |
| Vitamin K2 (MK-7) | up to ~4.8 µg in a grain-fermented sample; varies (Altuncu et al., 2024) | — |
| Live cultures | ~10⁸–10⁹ CFU/mL (fresh, grain-fermented); often lower in commercial products | — |
Whole-milk kefir adds fat and calories relative to the low-fat product above, with broadly similar protein and mineral content. Non-dairy kefir made from coconut milk or oat milk provides live cultures but typically less protein and, unless fortified, less calcium.
Kefir vs. Yogurt
Kefir and yogurt are both fermented milk, but they differ in starter culture, texture, alcohol and the strength of the research behind them. Kefir grains carry bacteria and yeasts and produce a drinkable, fizzy result; yogurt is fermented by bacteria alone and sets into a spoonable gel.
| Kefir | Yogurt | |
|---|---|---|
| Culture | Kefir grains: lactic acid bacteria, acetic acid bacteria and yeasts | L. bulgaricus and S. thermophilus, often with added probiotic strains |
| Texture | Thin, drinkable, slightly effervescent | Thick gel; strained (Greek) yogurt is thicker |
| Alcohol | Around 0.5% ethanol from the yeasts | Bacterial fermentation, no yeast stage |
| Live cultures | Lactobacilli ~10⁸–10⁹ CFU/mL in grain-fermented kefir; commercial counts often lower | Starter bacteria ~10⁸/mL in live-culture yogurt (Savaiano, 2014) |
| Protein per 100 g | 3.8 g (plain, low-fat) | 3.5 g (plain, whole-milk); about 10 g in plain Greek |
| Calcium per 100 g | 130 mg | 121 mg (plain, whole-milk) |
| Lactose-digestion evidence | One small trial in 15 adults | Consistent trials; recognised by EFSA |
Yogurt figures are USDA values for plain whole-milk yogurt (USDA FoodData Central) and plain Greek yogurt (USDA FoodData Central); the yogurt entry covers its evidence in detail. Neither food is clearly healthier for everyone. Greek yogurt suits someone prioritising protein, while kefir offers a broader microbial mix, though commercial counts vary widely.
Evidence for Purported Benefits
Human evidence for kefir is preliminary. Trials are few and small, and a 2025 meta-analysis of seven kefir trials found no overall effect on blood pressure or C-reactive protein.
Gut Microbiome Modulation
Evidence:Preliminary One small randomized study of a mixed fermented-food diet; kefir’s own contribution can’t be isolated.
A 2021 randomized study by Wastyk et al. (Cell, 2021) compared a high-fermented-food diet (including kefir) with a high-fiber diet in healthy adults over ten weeks. The fermented-food group showed significantly increased microbiome diversity and decreased markers of immune activation (19 inflammatory proteins), although the trial’s primary immune outcome (cytokine response score) did not change. Kefir-specific data are difficult to isolate because the intervention included multiple fermented foods.
Lactose Digestion
Evidence:Preliminary A single small trial in 15 adults with lactose maldigestion.
A small randomized trial by Hertzler and Clancy (Journal of the American Dietetic Association, 2003) in 15 adults with lactose maldigestion found that plain kefir produced less breath hydrogen than milk and reduced perceived flatulence severity; abdominal pain and diarrhea were negligible after all test meals. Microbial lactase activity is the proposed explanation.
Bone Health
Evidence:Preliminary One 6-month pilot RCT in osteoporotic patients; no independent replication yet.
Kefir provides calcium, phosphorus, protein, and fermentation-derived vitamin K2, nutrients involved in bone metabolism. A 6-month double-blind pilot RCT in osteoporotic patients by Tu et al. (PLoS One, 2015) reported that kefir-fermented milk plus calcium bicarbonate was associated with short-term changes in bone turnover markers and greater 6-month gains in hip bone mineral density than calcium carbonate alone.
Immune Modulation and Anti-inflammatory Effects
Evidence:Limited Mostly animal and in vitro work; a meta-analysis of seven small trials found no overall CRP effect, so results conflict.
Animal and in vitro studies report that kefiran and kefir-derived peptides modulate cytokine production and other immune responses (Rosa et al., 2017). Human randomized trials are few and mostly small: a 2025 meta-analysis of seven trials found no significant overall effect of kefir on C-reactive protein, with a decrease seen only in a subgroup of trials lasting 8 weeks or longer (Rashidbeygi et al., 2025).
Blood Pressure
Evidence:Insufficient A meta-analysis of seven kefir RCTs found no blood pressure change; the modest effect seen is for probiotic fermented milks generally.
ACE-inhibitory peptides produced during kefir fermentation have attracted research interest. A meta-analysis by Dong et al. (British Journal of Nutrition, 2013) of 14 placebo-controlled trials of probiotic fermented milk (not kefir exclusively) found a modest reduction of about 3 mmHg in systolic and 1 mmHg in diastolic blood pressure, with some evidence of publication bias. Kefir-specific trials have not confirmed an effect: a 2025 meta-analysis of seven kefir RCTs found no significant change in systolic or diastolic blood pressure (Rashidbeygi et al., 2025).
Typical Use and Preparation
Photo: Quijote at Russian Wikipedia, CC BY-SA 3.0, via Wikimedia Commons
Kefir is consumed as a beverage, used as a base for smoothies, or substituted for buttermilk in baking. Plain, minimally processed kefir retains the highest viable probiotic counts. Cooking or baking destroys live cultures, so kefir added to hot dishes provides nutritional value (calcium, protein) but not probiotic activity.
Commercial kefir in most markets is pasteurized, homogenized, and inoculated with defined starter cultures rather than traditional grains; probiotic counts and strain diversity typically differ from traditionally prepared grain-fermented kefir. Consumers seeking live cultures should look for products labeled “contains live and active cultures.”
Water kefir (tibicos) is a non-dairy alternative fermented with different grain communities and provides probiotics without dairy proteins or lactose.
The gut-health guide covers kefir alongside yogurt, kimchi, and other fermented foods. For a non-dairy fermented drink made with a different culture, see kombucha.
Safety, Interactions, and Contraindications
The main cautions with kefir concern biogenic amines, raw-milk products, live cultures in severe immunosuppression, trace alcohol, and milk allergy.
Histamine content: Kefir can contain biogenic amines such as histamine and tyramine, formed by bacterial decarboxylation of amino acids during fermentation. One analysis found them frequently in kefir samples at levels not considered a concern for the general population but relevant to sensitive individuals (Moniente et al., 2023). Individuals with histamine intolerance or those taking monoamine oxidase inhibitors (MAOIs) should exercise caution, as MAOI combined with high-tyramine foods can produce hypertensive crises. Consultation with a prescribing clinician is recommended before regular consumption.
Raw milk and immunocompromised individuals: Kefir made from raw (unpasteurized) milk can carry pathogens such as Listeria, Salmonella, and E. coli O157:H7, and the FDA identifies pregnant women, older adults, and immunocompromised people as most at risk from raw-milk products (FDA). Separately, lactobacilli of the kinds used as live cultures have occasionally been reported to cause bloodstream infections and endocarditis in vulnerable patients (Rossi et al., 2022), so people who are severely immunocompromised (e.g., receiving chemotherapy or after organ transplant) should ask their care team before consuming live-culture products.
Sodium: Commercially flavored kefir products may contain added sugar and moderate sodium. Plain varieties are low in sodium (about 40 mg/100 g; USDA FoodData Central).
Alcohol content: Kefir contains small amounts of ethanol, typically around 0.5% and up to about 1% with a heavier grain inoculum (Farag et al., 2020); this is relevant for individuals avoiding alcohol for medical, religious, or personal reasons.
Dairy allergy vs. lactose intolerance: Kefir is inappropriate for individuals with IgE-mediated cow’s milk protein allergy, regardless of its reduced lactose content.
This information is educational and does not constitute medical advice. Consult a qualified healthcare provider before making changes to your diet, particularly if you have an underlying health condition.
Frequently Asked Questions
Which is healthier, kefir or Greek yogurt?
It depends on the goal. Plain Greek yogurt has about 10 g of protein per 100 g, against 3.8 g in plain low-fat kefir, so it is the stronger protein source. Kefir carries a wider range of bacteria and yeasts. Calcium is similar between kefir and regular yogurt, while straining lowers it somewhat in Greek yogurt. Neither has strong human evidence of superior health effects.
Is kefir good for you?
Kefir is a nutritious dairy food, supplying protein, calcium, riboflavin and vitamin B12 at 43 kcal per 100 g for the low-fat plain version. Evidence for specific benefits is preliminary: a small trial found it improved lactose digestion compared with milk, and a pilot trial reported bone-density changes in osteoporotic patients. Kefir-specific trials have not shown effects on blood pressure.
Is there any downside to kefir?
Kefir contains small amounts of alcohol (around 0.5%) and biogenic amines such as histamine and tyramine, which matter for people with histamine intolerance or those taking MAOIs. Raw-milk kefir can carry Listeria and other pathogens. Flavored products may add sugar. People with a cow’s milk protein allergy should avoid dairy kefir regardless of its lower lactose content.
How much kefir should you drink a day?
No official daily amount exists for kefir. A 200 mL glass of grain-fermented kefir can supply on the order of 10¹⁰ live lactobacilli, though commercial products often contain fewer than labeled. Studies have used different amounts and durations, so they do not define an optimal dose. People with a medical condition, or who are on MAOIs, should talk to a clinician first.
Is kefir alcoholic?
Kefir contains a little alcohol because its yeasts ferment some of the milk sugar. Levels are typically around 0.5%, with about 0.3–1% reported depending on how much grain is used. That is low, but it is relevant for anyone avoiding alcohol for medical, religious or personal reasons. Yogurt has no yeast stage and does not produce alcohol this way.
What is water kefir?
Water kefir, also called tibicos, is a non-dairy fermented drink made with a different community of grains and no milk. It provides live cultures without dairy proteins or lactose, so it is an option for people with a milk allergy or who avoid dairy. Without milk, it does not supply the protein and calcium that make milk kefir a useful dairy food.
References
Show all 17 referencesShow fewer
- Wastyk, H. C., et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell, 184(16), 4137–4153.
- Hertzler, S. R., & Clancy, S. M. (2003). Kefir improves lactose digestion and tolerance in adults with lactose maldigestion. Journal of the American Dietetic Association, 103(5), 582–587.
- Tu, M. Y., Chen, H. L., Tung, Y. T., Kao, C. C., Hu, F. C., & Chen, C. M. (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, 10(12), e0144231.
- Dong, J. Y., Szeto, I. M., Makinen, K., et al. (2013). Effect of probiotic fermented milk on blood pressure: a meta-analysis of randomised controlled trials. British Journal of Nutrition, 110(7), 1188–1194.
- Rosa, D. D., et al. (2017). Milk kefir: Nutritional, microbiological and health benefits. Nutrition Research Reviews, 30(1), 82–96.
- Bourrie, B. C. T., et al. (2016). The microbiota and health promoting characteristics of the fermented beverage kefir. Frontiers in Microbiology, 7, 647.
- Farag, M. A., et al. (2020). The many faces of kefir fermented dairy products: Quality characteristics, flavour chemistry, nutritional value, health benefits, and safety. Nutrients.
- Metras, B. N., et al. (2021). Commercial kefir products assessed for label accuracy of microbial composition and density. JDS Communications.
- Altuncu, V., et al. (2024). Evaluation of menaquinone-7 and fat-soluble vitamin production by starter cultures during fermentation in dairy products using RPLC method. Food Science & Nutrition, 12(11), 9822–9833.
- USDA FoodData Central. Kefir, lowfat, plain, LIFEWAY (FDC ID 170904).
- Rashidbeygi, E., et al. (2025). The effect of kefir consumption on blood pressure and C-reactive protein: A systematic review and meta-analysis of randomised controlled trials. Endocrinology, Diabetes & Metabolism.
- Moniente, M., et al. (2023). Combination of SPE and fluorescent detection of AQC-derivatives for the determination at sub-mg/L levels of biogenic amines in dairy products. Food Research International.
- Rossi, F., et al. (2022). Lactobacilli infection case reports in the last three years and safety implications. Nutrients, 14(6), 1178.
- U.S. Food and Drug Administration. Raw milk misconceptions and the danger of raw milk consumption.
- Savaiano, D. A. (2014). Lactose digestion from yogurt: mechanism and relevance. American Journal of Clinical Nutrition, 99(5 Suppl), 1251S–1255S.
- USDA FoodData Central. Yogurt, plain, whole milk (FDC ID 171284).
- USDA FoodData Central. Yogurt, Greek, plain (FDC ID 170894).
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Curated by Superfoods Advisor Editors·Last updated