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One of the most notable shifts in wellness conversations in recent years has been a growing emphasis on gut health. As research increasingly explores how the gut microbiome may affect everything from digestion and immune function to metabolism and brain health, many of us are better recognizing its influence and importance.
Among other things, this has led to increased interest in – and demand for – probiotics and fermented foods like yogurt, kimchi and drinks such as kefir.
“One of the reasons people are drawn to kefir is that it combines the convenience of a drink with the nutritional benefits of a fermented food,” says Perri Halperin, a registered dietitian and clinical nutrition coordinator for the Mount Sinai Health System. It’s also “an easy way to add probiotics to your diet,” she adds.
But kefir doesn’t necessarily deliver every benefit attributed to it, and it isn’t right for everyone. Here’s what to know.
What is kefir?
Kefir is a fermented beverage traditionally produced by adding kefir grains to cow’s, goat’s or sheep’s milk, explains Halperin. There’s also water kefir, a related non-dairy drink made by fermenting sweetened water or juice with a different culture.
In either case and despite the similar name and appearance, kefir grains aren’t cereal grains, but are “soft clusters made up of beneficial bacteria, yeasts, proteins and polysaccharides,” Halperin explains. When added to milk and left to ferment, typically for 12 to 24 hours, they break down some of the drink’s lactose and produce lactic acid, carbon dioxide and other compounds. This gives kefir its fermented qualities. “The result is a creamy, tangy beverage that’s slightly tart and often has a mild natural fizz,” Halperin says.
At the same time, while “traditional kefir tends to be more tart and contains a wider variety of microbes,” explains Laura Bellows, a registered dietitian and professor in the division of nutritional sciences at Cornell University, “many store-bought versions have a milder taste and more standardized cultures.”
Some commercial products are also flavored, sweetened or heat-treated after fermentation. While heat can help extend shelf life and improve product stability, it can also eliminate living microorganisms, so shoppers specifically seeking probiotics in their kefir should look for “live and active cultures” on the label.
Is drinking kefir actually good for you?
Kefir has several nutritional advantages as it combines the nutrients naturally present in milk with the microorganisms, compounds and living cultures produced during fermentation. Among them, “kefir is best known for its probiotics, which help support a healthy gut microbiome,” says Bellows. Probiotics may also help with digestion and maintaining a healthy balance of microorganisms in the gut. “And depending on the probiotic strains present in each variety of the drink,” says Halperin, probiotics can also help maintain the gut barrier and support immune function.
And with one cup of plain kefir “providing about 8 to 11 grams,” kefir is also a source of complete protein, which supports muscle maintenance, tissue repair, immune function and satiety, says Halperin.
The drink “also provides calcium for bone and muscle health,” says Bellows, “along with B vitamins that help convert food into energy.” These B vitamins also “support healthy nerves, aid red blood cell production and contribute to normal brain function,” adds Halperin. Some kefir products also contain added vitamin D, which further supports bone and immune health and helps the body better absorb calcium. And kefir contains potassium and phosphorus, Halperin notes, which are important for fluid balance, muscle and nerve function and bone health.
The fermentation process also reduces kefir’s lactose content because its microorganisms consume some of the milk sugar. Because of this, Halperin says many people with mild lactose intolerance tolerate kefir better than ordinary milk, though kefir is not lactose-free unless labeled accordingly.
Researchers are also investigating whether kefir can influence inflammation, cholesterol, blood pressure and blood-sugar control, but a systematic review of randomized trials found that human evidence for these and other purported benefits remains limited.
Can you drink kefir every day? And when to not drink kefir
Most healthy adults can consume kefir regularly, says Halperin, but there are a few things to consider when doing so. For one, beginners may want to start with smaller portions of the drink “because mild gas or bloating can occur while the gut adjusts,” Bellows says.
There are nutritional tradeoffs to consider as well, though they largely depend on the product. Whole-milk varieties contain more calories and fat – about 140 calories and 8 grams of fat per cup – while skim, 1% and 2% varieties generally contain less. “But added sugars are the biggest concern with store-bought kefir,” cautions Halperin, “as some flavored commercial kefirs contain 10 to 20 grams or more of added sugars per serving, depending on the brand.”
And anyone with a milk allergy should avoid dairy kefir because “fermentation does not remove the milk proteins that trigger an allergic reaction,” Halperin explains.
Consumers should also be aware that fermentation naturally produces a small quantity of alcohol, with levels potentially less predictable in homemade kefir. “And people with chronic kidney disease may need to account for kefir’s potassium, phosphorus and protein content as part of their overall diet, depending on the stage of disease and their care plan,” Halperin adds. And because kefir contains living microorganisms, organ-transplant recipients, people undergoing intensive chemotherapy and others with compromised immunity should consult their health care team before drinking it.
For everyone else, Bellows says, kefir can be a convenient source of probiotics, protein and key vitamins and minerals, “and can be a valuable addition to a balanced diet.”