What are the health benefits and risks of kefir?
Kefir is a fermented food or drink usually made from milk. It’s a bit like yogurt but with a more sour, tangy flavor.
People have been making kefir for thousands of years using a naturally occurring collection of bacteria, yeasts, and other microorganisms called kefir “grains.”
Kefir contains millions of probiotics, which are bacteria with potential health benefits. It’s also low in lactose and packed with vitamins and minerals that are good for your body.
Scientists have found a range of possible health benefits of kefir, including improved cholesterol, blood sugar control, and gut health. It also has a reputation for helping with weight loss.
Below, we’ll look at the science behind these claims, as well as any risks to be aware of. We’ll also delve further into what kefir is, how it’s made, the different kinds of kefir, and some ideas for how to use it.
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What is kefir?
Kefir is a fermented drink traditionally made from milk.
It originated thousands of years ago in the mountains of the North Caucasus region of Russia, as well as in Tibet and Mongolia. People began producing and consuming kefir more widely during the 19th century.
While people have always consumed kefir for its supposed benefits, it has recently become more popular in the West. In fact, these days, it’s available in most grocery stores.
The probiotics, or “good” bacteria, in kefir are part of the reason it may have health benefits.
Interestingly, the kefir “grains,” the bacteria and yeast used in the fermentation process, came about naturally and can’t be produced artificially. This means that the grains used to make kefir today are direct descendants of those first discovered thousands of years ago.
Despite the name, kefir grains are not grains in the usual sense. They’re actually a collection of bacteria, yeast, and other microorganisms. When clumped together, they look a bit like cauliflower or cottage cheese.
The microorganisms in kefir grains are symbiotic, meaning they can exist together without the need for other food. However, when kefir grains are added to milk, the bacteria and yeast use it as food and multiply. This starts the process of fermentation.
Fermentation occurs when microorganisms turn food into other chemicals, changing the flavor and creating healthy nutrients.
However, some mass-produced kefir products use bacteria and yeasts extracted from kefir grains rather than the grains themselves. This reduces the number and diversity of probiotics in the kefir.
Types of kefir
There are different types of kefir made from distinct kefir grains.
Milk kefir is the most common type, but kefir drinks made from water are popular, too.
While water kefir is a good choice if you’re vegan, it has different probiotics than milk kefir and doesn’t contain the protein that comes from the dairy in milk.
Milk kefir itself comes in both full-fat and low-fat versions. The higher the fat content in the milk, the thicker and creamier the kefir, so higher fat kefir is actually less like a drink and more like yogurt.
In fact, full-fat kefir has similar protein, fat, and sugar content to full-fat yogurt.
A 100-milliliter (ml) serving of plain whole milk kefir has about:
4 grams (g) protein
4 g fat
3 g sugar
However, thick kefir and yogurt are not the same.
While “live” yogurts do contain probiotics, kefir made from kefir grains has a much more diverse range — around 300 different species — including some that are only present in kefir.
As we’ll see below, kefir also has much less lactose than yogurt, which can be good to know if you have lactose intolerance.
Kefir contains a range of B vitamins, as well as vitamins C, A, and K. It’s a good source of essential minerals, including magnesium, calcium, and potassium.
Potential benefits of kefir
In fact, many of the probiotic bacteria in kefir are particularly good at surviving in the potentially harsh conditions in your gut.
There are claims linking kefir to improvements in cholesterol levels, blood pressure, blood sugar control, and weight loss.
Below, we’ll look at whether the science backs these up and consider some potential issues to be aware of before you start consuming kefir.
Cholesterol and blood pressure
Research suggests that eating probiotic foods may help lower both overall cholesterol and “bad” LDL cholesterol. When it comes to kefir specifically, things are less clear-cut.
Interestingly, one study found that a type of sugar molecule, kefiran, found in kefir grains, prevented blood pressure from increasing in rats that had been fed large amounts of cholesterol.
While probiotics, in general, do seem to have a positive effect on cholesterol levels and blood pressure, there’s currently not much research about kefir specifically.
Blood sugar control and diabetes
Prediabetes and insulin resistance — where your body doesn’t respond properly to the insulin it produces — are both risk factors for type 2 diabetes.
Studies suggest that regularly consuming probiotic foods and drinks may help to improve your body’s blood sugar control and reduce insulin resistance.
There’s also initial evidence that drinking kefir may improve these factors in people who already have diabetes.
In one small study, people with type 2 diabetes consumed either 600 ml of kefir or a different type of fermented milk daily.
After 8 weeks, participants who consumed kefir saw a significant decrease in their blood sugar measurements compared with the control group.
Consuming kefir regularly may contribute to weight loss, but the limited evidence suggests it’s no more effective than drinking skim milk.
In one study, researchers divided 58 women with overweight or obesity into three groups. They all followed a weight-maintenance diet that included two servings of low-fat dairy products each day.
However, one group also included two more servings of low-fat milk in their daily diet, while another group included two servings of kefir.
After 8 weeks, the women consuming extra milk or kefir had lost significantly more weight than those in the control group and reduced their waist measurements and body mass index.
However, there was no difference between the results in the kefir and milk groups.
Gut health and lactose intolerance
As we’ve seen, eating fermented foods can improve the balance and diversity of the bugs in your gut microbiome. This could have benefits across a range of digestive issues, including some forms of diarrhea and certain aspects of irritable bowel syndrome.
Kefir may also be able to help with lactose intolerance, a common digestive issue that can lead to symptoms such as excess gas and bloating.
Lactose intolerance happens when your body can’t properly digest the dairy sugar lactose. It’s usually due to not having enough of an enzyme called beta-galactosidase, which helps break lactose down.
However, beta-galactosidase is naturally present in kefir grains, so during fermentation, it reduces the amount of lactose in the milk by around 30%. Certain enzymes in the kefir itself can also help you to digest the remaining lactose once you’ve consumed it.
In one small study, people with lactose intolerance reported that kefir reduced their gas by half compared with milk. It also improved lactose digestion.
However, the same was true for yogurt, so more research is needed to see if there’s really a significant difference between the two.
Inflammation can be a good thing: It's a response by your immune system to illness or injury that helps you fight off disease or heal properly.
But chronic inflammation — a continuing, unwanted immune response — can be bad for your body. This can lead to long-term health conditions like arthritis, heart disease, stroke, and type 2 diabetes.
Most research into the effects of kefir on inflammation comes from laboratory and animal studies. They’ve shown that substances in kefir can reduce the activity of proteins that activate immune responses and cause inflammation.
Scientists are now beginning to look at kefir and inflammation in people.
Potential risks of consuming kefir
For most people, fermented foods like kefir are considered safe. But when you first take probiotics, you may experience digestive issues like increased gas, bloating, or diarrhea. These usually settle down after a few days as your body adjusts.
Although milk kefir is much lower in lactose than most dairy products, people who are very lactose intolerant may still need to be careful about how much they consume. Luckily, there are non-dairy forms of kefir that also have probiotic effects.
If you want to avoid lactose entirely, you could drink water kefir, which should usually have no dairy at all. Alternatively, you could try fruit juice kefir, but be mindful of its sugar content.
It’s worth being aware that the kefir fermentation process produces a small amount of alcohol. Kefir can contain between 0.5% and 2% alcohol, so you may want to check the label before you buy.
If you have an immune deficiency or have recently had surgery, you may be at an increased risk of infection. You should talk to your doctor before taking probiotics.
How to have kefir
If you’re new to kefir, start by consuming a small amount at a time. This will give your gut the chance to get used to the probiotic bugs, and it will let you get a taste for the tangy, sour flavor.
In fact, ZOE co-founder Prof. Tim Spector, a professor of epidemiology at King’s College London, suggests having “a small shot of fermented foods daily, rather than consuming a large amount of fermented food once in a while.”
Consuming probiotic bacteria regularly may give these “good” bugs a better chance of hanging around in your gut. Make sure to also include plenty of different plants in your diet. These provide prebiotics that feed your “good” gut bugs and help them to thrive.
If you’re drinking kefir on a daily basis, there are lots of things you can do to keep it interesting.
mixed into yogurt
in a smoothie
in salad dressings
Kefir is a versatile fermented food packed with probiotics and healthy nutrients.
Although it has a reputation as a health food, most of the science looking at kefir has been done in laboratory or animal research, and hasn’t involved people.
Nevertheless, kefir shows promise in areas including blood sugar control and gut health, and it’s generally considered safe for most people.
With ZOE’s at-home test, you can learn all about the bacteria that live in your gut and get personalized recommendations for foods to help improve your gut health.
You can find out more by taking our free quiz.
A big world in small grain: a review of natural milk kefir starters. Microorganisms. (2020). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7074874/
A comparison of milk kefir and water kefir: physical, chemical, microbiological and functional properties. Trends in Food Science & Technology. (2021). https://www.sciencedirect.com/science/article/abs/pii/S0924224421003010
A meta-analysis of probiotic efficacy for gastrointestinal diseases. PLoS One. (2012). https://pubmed.ncbi.nlm.nih.gov/22529959/
A review: chemical, microbiological and nutritional characteristics of kefir. CyTA Journal of Food. (2014). https://www.tandfonline.com/doi/full/10.1080/19476337.2014.981588
A systematic review and meta-analysis: probiotics in the treatment of irritable bowel syndrome. BMC Gastroenterology. (2009). https://pubmed.ncbi.nlm.nih.gov/19220890/
Characterization of homofermentative lactobacilli isolated from kefir grains: potential use as probiotic. The Journal of Dairy Research. (2008). https://pubmed.ncbi.nlm.nih.gov/18474139/
Chronic inflammatory disorders and risk of type 2 diabetes mellitus, coronary heart disease, and stroke. Circulation. (2014). https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.114.009990
Effect of probiotic fermented milk (kefir) on glycemic control and lipid profile in type 2 diabetic patients: a randomized double-blind placebo-controlled clinical trial. Iranian Journal of Public Health. (2015). https://pubmed.ncbi.nlm.nih.gov/25905057/
Effects of an exopolysaccharide (kefiran) on lipids, blood pressure, blood glucose, and constipation. BioFactors. (2004). https://pubmed.ncbi.nlm.nih.gov/15630283/
Effects of Lactobacillus plantarum MA2 isolated from Tibet kefir on lipid metabolism and intestinal microflora of rats fed on high-cholesterol diet. Applied Microbiology and Microtechnology. (2009). https://pubmed.ncbi.nlm.nih.gov/19444443/
Efficacy and safety of probiotics in eradicating Helicobacter pylori. Medicine. (2019). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6485819/
Fermented foods: definitions and characteristics, impact on the gut microbiota and effects on gastrointestinal health and disease. Nutrients. (2019). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6723656/
Gut microbiota, probiotics and diabetes. Nutrition Journal. (2014). https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-13-60
Influence of consumption of probiotics on the plasma lipid profile: a meta-analysis of randomised controlled trials. Nutrition, Metabolism, and Cardiovascular Diseases. (2011). https://pubmed.ncbi.nlm.nih.gov/21930366/
Lactose intolerance. (n.d.). https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance
Kefir: a probiotic dairy-composition, nutritional and therapeutic aspects. Pakistan Journal of Nutrition. (2003). http://translateyar.ir/wp-content/uploads/2018/12/8721-English.pdf
Kefir: a protective dietary supplementation against viral infection. Biomedicine & Pharmacotherapy. (2021). https://www.sciencedirect.com/science/article/pii/S0753332220311665
Kefir consumption does not alter plasma lipid levels or cholesterol fractional synthesis rates relative to milk in hyperlipidemic men: A randomized controlled trial. BMC Complementary and Alternative Medicine. (2002). https://pubmed.ncbi.nlm.nih.gov/11825344/
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. European Journal of Nutrition. (2015). https://pubmed.ncbi.nlm.nih.gov/25648739/
Kefir improves lactose digestion and tolerance in adults with lactose maldigestion. Journal of the American Dietetic Association. (2003). https://pubmed.ncbi.nlm.nih.gov/12728216/
Milk kefir: composition, microbial cultures, biological activities, and related products. Frontiers in Microbiology. (2015). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4626640/
Milk kefir: nutritional, microbiological and health benefits. Nutrition Research Reviews. (2017). https://www.cambridge.org/core/journals/nutrition-research-reviews/article/milk-kefir-nutritional-microbiological-and-health-benefits/1393DC2B8E5F08B0BE7BD58F030D387B
Mini review on role of β-galactosidase in lactose intolerance. IOP Conference Series: Materials Science and Engineering. (2017). https://iopscience.iop.org/article/10.1088/1757-899X/263/2/022046/pdf
Plain kefir. (2018). https://fdc.nal.usda.gov/fdc-app.html#/food-details/432442/nutrients
Probiotics: if it does not help it does not do any harm. Really?. Microorganisms. (2019). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6517882/
The many faces of kefir fermented dairy products: quality characteristics, flavour chemistry, nutritional value, health benefits, and safety. Nutrients. (2020). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7071183/
The therapeutic effect of probiotic bacteria on gastrointestinal diseases. Advances in Clinical and Experimental Medicine. (2013). https://pubmed.ncbi.nlm.nih.gov/24285463/