Kefir is a fermented milk drink and one of the most microbially diverse fermented foods available, typically containing 10 to 20 different species of bacteria and yeasts. That diversity is what sets it apart from most other fermented foods and from many probiotic supplements. Last reviewed: July 2026.
Here is what the research actually shows about kefir, how it compares to yoghurt and to probiotic capsules, and how to use it sensibly.
Table of Contents
What is kefir?
Kefir is made by adding kefir grains, a symbiotic culture of bacteria and yeasts held together in a matrix of proteins and a polysaccharide called kefiran, to milk. The grains ferment the milk over around 24 hours, producing lactic acid, a small amount of carbon dioxide, trace alcohol, and a large population of live cultures. The result is a tart, slightly effervescent drink with a thinner texture than yoghurt.
The word kefir comes from the Turkish “keyif”, loosely meaning good feeling. It has been consumed in the Caucasus region for centuries, long before the microbiology was understood.
Milk kefir vs water kefir
Milk kefir is the traditional form and the one with the most research behind it. Water kefir is made by fermenting sugared water or fruit juice with a different set of grains, and it offers a comparable diversity of live cultures in a dairy-free format, though it is less studied. If you avoid dairy, water kefir is the closer match to the traditional product than most other alternatives. For more on choosing dairy-free options, see our guide to dairy-free probiotic drinks.
What are the benefits of kefir?
Microbiome diversity
The strongest case for kefir rests on its diversity. A diverse gut microbiome is consistently associated with better health outcomes, and kefir delivers a broader range of live organisms than most single-strain or few-strain products. A review in Nutrition Research Reviews (Rosa et al., 2017) summarised evidence that kefir supports microbiome balance, digestion, and immune function, drawing on both animal and human studies.
Lactose digestion
Kefir is often better tolerated than milk by people who are lactose sensitive. The fermentation process breaks down a significant portion of the lactose, and the live cultures themselves produce lactase, the enzyme that digests lactose. Research has found that fermented dairy containing these cultures reduces lactose maldigestion symptoms compared with unfermented milk.
Immune and gut barrier support
Several of the organisms found in kefir, including Lactobacillus species and Streptococcus thermophilus, have been studied for their effects on the gut lining and immune signalling. The mechanisms overlap with those seen for other fermented foods: organic acids that lower gut pH, and bioactive compounds that support the intestinal barrier.
Antimicrobial activity
Kefiran, the polysaccharide produced by kefir grains, and the organic acids generated during fermentation have both shown antimicrobial activity in laboratory studies, helping to suppress the growth of potentially harmful bacteria. This is part of why traditionally fermented foods create an environment less hospitable to pathogens.
A note on what kefir cannot do
Kefir is a food, not a medicine. The evidence supports it as a useful part of a varied, fibre-rich diet, but claims that it cures conditions or dramatically transforms health are not supported. Treat it as one consistent input among several, not a single fix.
Kefir vs yoghurt
Both are fermented dairy, but kefir is fermented by a broader mix of bacteria and yeasts, while yoghurt is typically fermented by two main bacterial species. That gives kefir greater microbial diversity. Yoghurt is thicker because it is fermented differently and is an excellent food in its own right, but if diversity of live cultures is the goal, kefir generally comes out ahead. Choosing plain, unsweetened versions of either avoids the added sugar that can work against the gut benefit.
Kefir vs probiotic supplements
This is where kefir gets interesting. Standard probiotic capsules deliver a small number of specific strains in a dried, non-fermented base. Kefir delivers a diverse community of live cultures within a fermented matrix, alongside the organic acids and postbiotic compounds produced during fermentation. Research on fermented foods more broadly, including a 2021 Stanford study in Cell, suggests that delivering live cultures within a fermented matrix may support microbiome diversity more effectively than isolated strains in a capsule.
This is the same principle behind Biome Bliss, which is made by natural fermentation rather than by adding dried cultures to a non-fermented base. It does not contain kefir grains or replicate kefir’s specific strains, but it shares kefir’s fermented-delivery logic: live cultures grown within a fermented liquid, plus the postbiotic compounds that fermentation produces. One practical difference: kefir is usually dairy based, whereas Biome Bliss is fermented on a base of organic apple juice, organic honey and water, so it suits people who prefer to avoid dairy. For those who want the fermented-food principle in a consistent daily dose, it sits alongside foods like kefir rather than replacing them. For a fuller comparison of formats, see our guide to gut health drinks.
How much kefir should you drink?
There is no official recommended amount. A practical starting point is a small glass, around 100 to 150ml, once a day, building up gradually. Kefir is potent, and introducing it slowly gives your gut time to adjust and reduces the temporary bloating some people notice at first. As with all fermented foods, consistency matters more than quantity. A modest amount every day does more than a large amount occasionally.
For where kefir fits in a broader gut strategy, see our guides to fermented foods and gut health and improving gut health.
Frequently Asked Questions
What are the main benefits of kefir?
Kefir’s main strength is microbial diversity, typically 10 to 20 species of bacteria and yeasts, which supports a diverse gut microbiome. It is also often better tolerated than milk by lactose-sensitive people, because fermentation breaks down much of the lactose and the cultures produce lactase. It provides live cultures and postbiotic compounds within a fermented matrix.
Is kefir better than yoghurt?
For diversity of live cultures, kefir generally comes out ahead, because it is fermented by a broader mix of bacteria and yeasts than yoghurt. Yoghurt is still an excellent fermented food. Choosing plain, unsweetened versions of either matters more than the choice between them.
Is kefir better than a probiotic supplement?
Kefir delivers a diverse community of live cultures within a fermented matrix, rather than a few isolated strains in a capsule. Research on fermented foods suggests this format may support microbiome diversity well. A naturally fermented supplement that shares this fermented-delivery approach can complement fermented foods like kefir.
Can you drink kefir if you are lactose intolerant?
Many lactose-sensitive people tolerate milk kefir better than milk, because fermentation reduces its lactose content and the cultures produce lactase. Tolerance varies, so introduce it slowly. Water kefir is a dairy-free alternative for those who avoid dairy entirely.
How much kefir should I drink a day?
There is no official amount. A small glass of around 100 to 150ml once a day is a sensible starting point, built up gradually. Consistency matters more than quantity.
Does kefir have any side effects?
Some people notice temporary bloating or changes in digestion when they first start, which usually settle as the gut adjusts. Introducing kefir slowly reduces this. If you are immunocompromised or have a serious health condition, speak to your doctor before adding live-culture foods.
References
- Rosa DD et al. (2017). Milk kefir: nutritional, microbiological and health benefits. Nutrition Research Reviews, 30(1), 82-96.
- Wastyk HC et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell, 184(16), 4137-4153.
- Bourrie BCT et al. (2016). The microbiota and health promoting characteristics of the fermented beverage kefir. Frontiers in Microbiology, 7, 647.
This article is for informational purposes only and does not constitute medical advice. Please consult a GP or registered healthcare professional before making significant dietary changes, particularly if you are immunocompromised or have a medical condition.
