Kefir
(3-4 minute read)
What is kefir?
Kefir is a traditional fermented drink that originated in the Caucasus Mountains, where it has been consumed for generations. For decades, it has attracted the attention of scientists and is now one of the most studied fermented foods. Traditionally, kefir is made by fermenting milk with kefir grains, creating a complex community of bacteria and yeasts that work together to produce a drink rich in live microorganisms.
The strongest evidence for kefir's health benefits relates to lactose digestion and digestive health. Research into its potential effects on the gut microbiome, immune function, and metabolic health is also promising, although the evidence is still evolving.¹
What does the evidence say?
Kefir's health effects are thought to come largely from its live microorganisms and the compounds they produce during fermentation.
Kefir & digestive health: Among fermented foods, kefir has some of the strongest evidence for improving lactose digestion. During fermentation, microorganisms break down much of the lactose naturally present in milk, making kefir easier to tolerate for some people with lactose intolerance.²
One of the earliest clinical trials found that adults with lactose intolerance digested lactose significantly better after drinking kefir, compared to drinking regular milk. Kefir reduced the amount of undigested lactose reaching the gut by around 60% and reduced symptoms such as gas and bloating by more than half.³
Kefir & the gut microbiome: Research suggests that kefir may influence the composition of the gut microbiome, with some studies reporting changes in bacterial groups associated with better health. A recent review highlighted that microorganisms from kefir could survive passage through the digestive tract and interact with the gut microbiome. This provides some evidence that fermented foods may influence the microbial environment of the gut.⁴
The evidence in this area is more nuanced than it is for digestive health. As noted in another review of clinical trials, it is difficult to produce consistent findings as kefir products are not standardised, meaning their microbial composition can vary considerably. The gut microbiome is also highly individual, making it challenging to determine exactly what changes kefir causes and how those changes translate into measurable health benefits.⁵
Despite these challenges, the overall direction of the research is encouraging. Current evidence suggests that microorganisms from kefir can survive digestion and may positively influence aspects of the gut microbiome.
Kefir & Immune function: Immune function describes how effectively the body's immune system protects against infection while maintaining a balanced inflammatory response. Research suggests that kefir may support immune health by helping regulate inflammation, strengthening the gut's protective barrier, and limiting the growth of harmful bacteria.
The effects of kefir and its components on immune function have been evaluated and summarised in a review. The available evidence included in the paper suggests that the microorganisms and fermentation-derived compounds in kefir may support the activity of immune cells that help fight infection while reducing excessive inflammation. However, much of the evidence comes from laboratory and animal research, with relatively few human studies, meaning larger, high-quality clinical trials are still needed.⁶
Immune function and metabolic health are closely connected. The immune system is one of the body's most metabolically active systems, and immune cells constantly respond to changes in the body's metabolic state. As a result, kefir's potential effects on immune function and metabolic health are likely to be linked, with improvements in one area potentially influencing the other.
Metabolic health refers to how effectively the body processes and regulates energy from food, including blood sugar control, insulin function, and fat metabolism. Current evidence suggests that kefir may support metabolic health, with the strongest evidence pointing to improvements in insulin sensitivity.
For example, a review and analysis of studies found that kefir reduced fasting insulin levels and improved insulin resistance, although it had little effect on blood glucose, cholesterol, or body weight.⁷ Similarly, an early-stage study in mice found that whole kefir improved several markers of metabolic health and suggested that both its live microorganisms and fermentation-derived compounds contribute to these effects. While these findings are encouraging, studies in people are needed to confirm whether the same benefits occur.⁸
These effects may be linked to kefir's ability to support a healthy gut microbiome, strengthen the gut barrier, and reduce low-grade inflammation, all of which could contribute to better metabolic health. However, more high-quality human studies are needed before firm conclusions can be drawn.
Is kefir worth incorporating into the diet?
Beyond its live microorganisms, kefir is of high nutritional value. A typical 250 mL serving provides around 20–30% of an adult's daily calcium requirement, along with vitamin B12, riboflavin, phosphorus, and magnesium.
Kefir is available in several forms:
· Milk kefir
· Water kefir
· Kefir-style yogurt
· Ready-to-drink kefir
Kefir grains can also be purchased to make homemade kefir using milk or water.
The quality of kefir products varies, and with it, their potential benefits. The strongest research evidence comes from traditional drinkable milk kefir made with live kefir grains, as this is the form used in most clinical studies. Water kefir and kefir supplements are promising but have been studied less extensively, so it is not yet clear whether they provide the same health benefits. Kefir-style yogurt made with live kefir cultures is likely to offer similar nutritional value and comparable probiotic benefits. However, drinkable milk kefir currently has the strongest evidence supporting its health effects.⁹
Accessible kefir product options: These products reflect key characteristics of traditional kefir and closely align with the types of kefir most studied in research.
Biotiful Gut Health - Kefir Original
M&S – Good Gut Organic Whole Milk Kefir
Kefir bridges traditional nutrition with modern research. With the strongest evidence supporting its role in digestive health, ongoing research continues to explore its wider potential. Incorporating kefir into the diet offers an accessible way to include a nutrient-rich fermented food with promising benefits for gut health.
References:
1. Fijan S, Povalej Bržan P, Šikić Pogačar M, Klanjšek P. Kefir consumption and health effects based on human clinical trials: An overview of literature. Healthcare (Basel). 2026;14(5):652. doi:10.3390/healthcare14050652.
2. Savaiano DA, Hutkins RW. Yogurt, cultured fermented milk, and health: a systematic review. Nutr Rev. 2021;79(5):599-614. doi:10.1093/nutrit/nuaa013.
3. Hertzler SR, Clancy SM. Kefir improves lactose digestion and tolerance in adults with lactose maldigestion. J Am Diet Assoc. 2003;103(5):582-587. doi:10.1053/jada.2003.50111.
4. Hamsho M, Ranneh Y, Kaddour B, Alfakhri S, Hacıbayram H, Shkorfu W, et al. Kefir: A potential gut microbiota modulator: a systematic review of human interventional studies. MicrobiologyOpen. 2026;15(3):e70297. doi:10.1002/mbo3.70297.
5. Kairey L, Leech B, El-Assaad F, Bugarcic A, Dawson D, Lauche R. The effects of kefir consumption on human health: a systematic review of randomized controlled trials. Nutr Rev. 2023;81(3):267-286. doi:10.1093/nutrit/nuac054.
6. Culpepper T. The effects of kefir and kefir components on immune and metabolic physiology in pre-clinical studies: a narrative review. Cureus. 2022 Aug 8;14(8):e27768. doi:10.7759/cureus.27768.
7. Yahyapoor F, Haghighat N, Sohrabi Z, Asbaghi O, Bagherniya M, Jamialahmadi T, Sahebkar A. Effects of kefir consumption on cardiometabolic risk factors: a systematic review and meta-analysis of randomized controlled trials. Curr Drug Targets. 2023;24(7):599-612. doi:10.2174/1389450124666230427095742.
8. Bourrie BCT, Forgie AJ, Ju T, Richard C, Cotter PD and Willing BP. Consumption of the cell-free or heat-treated fractions of a pitched kefir confers some but not all positive impacts of the corresponding whole kefir. Front Microbiol. 2022;13:1056526. doi:10.3389/fmicb.2022.1056526.
9. Bourrie BC, Willing BP, Cotter PD. The microbiota and health promoting characteristics of the fermented beverage kefir. Front Microbiol. 2016 May 4;7:647. doi:10.3389/fmicb.2016.00647.