Kefir: Benefits, Evidence and How to Make It

Reviewed and written by Dr Zeeshan Afzal, MBBS — Medical Doctor and Clinical Content Lead at Welzo. Last updated: July 2026. This article is for general information and is not a substitute for individual medical advice.

Kefir has moved from Eastern European kitchen staple to British supermarket shelf in under a decade, and the questions I hear most often in clinic are simple ones: does it actually do anything, and is it worth making at home? The short answer is that kefir is one of the better-evidenced fermented foods for gut health, with human trial data supporting improved lactose digestion, better bowel regularity and measurable shifts in the gut microbiome — though several of the bolder claims made online run well ahead of the evidence.

Below I have set out what the research genuinely supports, where it does not, and a tested, food-safe method for making milk and water kefir at home. If you are building a broader gut routine, it is worth reading this alongside our guides to gut health in the UK, microbiome diversity, fermented foods and the best probiotics in the UK. You can browse Welzo's clinically screened probiotics range, our Akkermansia muciniphila and citrus pectin powder, plus targeted formulas such as Welzo Ultra Purity Berberine and Welzo Ultra Purity TUDCA.

Table of contents

• What is kefir?
• Kefir nutrition: what is actually in a glass
• Kefir benefits: what the evidence shows
• Evidence strength at a glance
• How to make kefir at home
• How to make water kefir
• How much kefir should you drink?
• Kefir vs probiotic supplements
• Who should be cautious with kefir
• How to choose shop-bought kefir in the UK
• Frequently asked questions
• References

What is kefir?

Kefir is a fermented milk drink made by adding kefir grains to milk and letting the mixture ferment at room temperature for roughly 24 hours. The result is tart, mildly fizzy and pourable — closer to a drinking yoghurt than a set yoghurt. It originated in the Caucasus Mountains and has been consumed there for centuries.

What makes kefir distinctive is not simply that it is fermented, but what ferments it. Kefir grains are a symbiotic community of lactic acid bacteria and yeasts held together in a polysaccharide matrix called kefiran. A single batch of milk kefir can therefore contain a considerably wider range of microbial species than a standard yoghurt, which typically relies on two defined starter strains.

Milk kefir versus water kefir

Two quite different drinks share the name. Milk kefir is fermented dairy — cow, goat or sheep milk — and is the version studied in most clinical trials. Water kefir (also called tibicos) uses a different grain culture to ferment sugar water, often with fruit or coconut water. Water kefir is dairy-free and vegan, but it contains almost no protein or calcium and has a much thinner evidence base. If you are avoiding dairy, our guides to dairy-free probiotics and vegan probiotics cover the alternatives in more detail.

What are kefir grains?

Despite the name, kefir grains contain no cereal grain. They are soft, irregular, cauliflower-like clusters that trap bacteria and yeasts within kefiran. They are living cultures: fed regularly with fresh milk, they grow and can be passed on indefinitely. This is why kefir grains are so often shared between households and why home-made kefir is markedly cheaper than shop-bought.

Kefir versus yoghurt: the practical differences

For a broader comparison of live cultures in food versus capsules, see our articles on kefir vs probiotics and fermented food vs probiotics.

Kefir nutrition: what is actually in a glass

Milk kefir is nutritionally close to the milk it was made from, with the lactose partially consumed during fermentation. Figures vary by brand, milk fat content and fermentation time, but the following gives a realistic working estimate for plain, low-fat milk kefir based on USDA FoodData Central composition data.

A 250 ml glass therefore supplies roughly 9–10 g of protein and around 300 mg of calcium — a meaningful contribution to daily requirements, before considering the live cultures at all. This matters clinically: much of the online discussion focuses exclusively on bacteria, but for older adults and anyone reducing dairy, kefir's protein, calcium and B12 content is a genuine benefit in its own right. Our guide to gut health in older adults covers this in more depth.

Kefir benefits: what the evidence shows

The research on kefir spans laboratory work, animal models and a modest number of human randomised controlled trials. Below I have separated what human studies support from what remains preliminary — an important distinction, because a great deal of the enthusiasm around kefir benefits rests on rodent data that has not yet been replicated in people.

1. It increases gut microbiome diversity

The strongest signal for fermented foods generally comes from a 2021 Stanford University randomised trial published in Cell. Thirty-six healthy adults were assigned to ten weeks of either a high-fermented-food diet — including kefir, yoghurt, kimchi, fermented vegetables and kombucha — or a high-fibre diet. The fermented-food group showed an increase in overall gut microbial diversity, with larger effects at larger servings, alongside reductions in 19 inflammatory proteins measured in blood, including interleukin-6. The high-fibre arm, notably, did not show the same increase in diversity over that timeframe.

Microbial diversity is one of the more consistent markers of a resilient gut ecosystem, and this trial is one of the few dietary interventions shown to move it reproducibly. If diversity is your goal, kefir works best as part of a wider pattern — see our guides to increasing gut bacteria diversity and the 30 plants a week approach.

2. It improves lactose digestion

This is the most reliably demonstrated of all kefir benefits. In a randomised study published in the Journal of the American Dietetic Association, 15 adults with diagnosed lactose maldigestion consumed test meals of milk, plain kefir, flavoured kefir, plain yoghurt and flavoured yoghurt, with breath hydrogen and symptoms monitored hourly for eight hours. Kefir improved both lactose digestion and symptom tolerance compared with milk.

The mechanism is straightforward: bacterial beta-galactosidase from the culture continues to break down lactose in the small intestine, and fermented products empty from the stomach more slowly, giving the enzyme more time to act. This does not make kefir suitable for people with a true cow's milk protein allergy — that is a separate immune reaction to protein, not sugar. Our articles on lactose intolerance supplements and foods that cause bloating explain the distinction.

3. It may help constipation and bowel regularity

A pilot study at Ege University in Turkey gave 500 ml of kefir daily for four weeks to 20 patients with functional constipation diagnosed by Rome II criteria. Participants showed increased stool frequency, improved stool consistency and reduced laxative use, with accelerated colonic transit in the slow-transit subgroup and improved bowel satisfaction scores.

This was an uncontrolled pilot with 20 participants, so the result should be treated as promising rather than definitive — the authors themselves called for controlled trials. Still, for someone with mild, uncomplicated constipation, a daily glass of kefir is a low-risk thing to trial for four weeks. Compare with the options in our guides to constipation relief, magnesium for constipation and the Bristol stool chart for tracking progress objectively.

4. It may improve Helicobacter pylori eradication

In a randomised, double-blind study of 82 patients with dyspepsia and confirmed H. pylori infection, participants received standard 14-day triple therapy — lansoprazole, amoxicillin and clarithromycin — with either 250 ml of kefir twice daily or a milk placebo. Eradication was achieved in 36 of 46 patients in the kefir group (78.2%) compared with 18 of 36 in the placebo group (50.0%), a statistically significant difference. Side effects were also reported less frequently in the kefir arm.

This aligns with wider meta-analyses showing that probiotic co-administration improves eradication rates and reduces treatment side effects. Kefir is an adjunct here, not a treatment — H. pylori requires prescribed antibiotic therapy. If this applies to you, read our guides on H. pylori, H. pylori testing, gastritis and stomach ulcers, and speak to your GP.

5. It may modestly improve blood sugar markers

A systematic review and meta-analysis of six randomised controlled trials involving 323 participants found that kefir consumption reduced fasting blood sugar and fasting insulin compared with control, but produced no statistically significant change in HbA1c. In practical terms: short-term glucose and insulin markers moved, the longer-term average did not reach significance.

That is a genuinely useful but modest finding, and it comes from a small pooled sample. Kefir is not a treatment for type 2 diabetes and should never replace prescribed medication. Related reading: gut health and blood sugar, berberine vs metformin and fibre and cholesterol.

6. Effects on blood pressure and inflammation are not established

Here the evidence is genuinely negative, and it deserves stating plainly. A 2025 systematic review and meta-analysis of seven randomised controlled trials in 385 adults found kefir had no significant effect on systolic blood pressure, diastolic blood pressure or C-reactive protein compared with control. A subgroup analysis did suggest CRP fell with longer durations of consumption of eight weeks or more, but the primary outcomes were null.

Anyone claiming kefir lowers blood pressure is overstating the current human evidence. This is a good example of why the distinction between preclinical and clinical data matters — kefir performs impressively in rodent models of metabolic syndrome, and that has not yet translated reliably to people.

7. It supports bone health through nutrition, not bacteria

Kefir's calcium, phosphorus, protein and vitamin K2 content contribute to bone maintenance in the same way other dairy products do. Fermentation may modestly improve mineral absorption by lowering pH. This is a straightforward nutritional benefit rather than a probiotic one, and it is often overlooked in favour of more speculative claims.

8. Antimicrobial and immune effects: mostly preclinical

Kefir and kefiran show antimicrobial activity against a range of pathogens in laboratory studies, and reviews consistently describe immunomodulatory and antioxidant properties. Most of this work is in vitro or in animals. The Stanford trial's reduction in inflammatory proteins is the clearest human immune-related signal to date, and that applied to fermented foods as a category rather than kefir specifically. Our guide to gut health and the immune system covers the underlying mechanisms.

9. Gut–brain effects: interesting but early

Fermented dairy has been studied in relation to mood and cognition through the gut–brain axis, and reviews have examined kefir components in neurodegenerative models. Human data specific to kefir is currently limited to small studies. Treat headlines about kefir and anxiety or memory with caution. For where the evidence is stronger, see the gut–brain connection, probiotics for anxiety and the vagus nerve and the gut.

10. Antibiotic-associated symptoms

Given the H. pylori trial results and the wider probiotic literature on antibiotic-associated diarrhoea, kefir is a reasonable food to include during and after a course of antibiotics — taken a couple of hours apart from the antibiotic dose. Our article on probiotics after antibiotics sets out the strain-specific evidence, and Saccharomyces boulardii has the better trial record for that particular indication.

Evidence strength at a glance

How to make kefir at home

Home fermentation is inexpensive, takes about five minutes of active work a day, and produces a drink with a considerably higher live microbe count than most pasteurised commercial versions. Here is the method I recommend.

What you need

• 1–2 tablespoons of live milk kefir grains
• 500 ml whole or semi-skimmed milk (pasteurised, not UHT if possible)
• A clean glass jar, roughly 750 ml
• A plastic or nylon sieve and a non-metallic spoon
• A breathable cover — muslin, kitchen paper or a coffee filter — plus an elastic band
• A second jar or bottle for storing the finished kefir

Prolonged contact with reactive metals such as aluminium or copper can damage the grains. Stainless steel for brief contact is generally fine, but plastic or nylon is the safer default.

Step-by-step: milk kefir

1. Combine. Place the grains in the jar and pour over the milk. A useful starting ratio is one tablespoon of grains per 250 ml of milk.
2. Cover. Secure the breathable cover with an elastic band. Do not seal the jar airtight — fermentation produces carbon dioxide, and a sealed jar can build pressure.
3. Ferment. Leave at room temperature, ideally 18–25°C, out of direct sunlight, for 18–24 hours. In a cold UK kitchen this may take up to 36 hours; in summer it may be ready in 12.
4. Check. The kefir is ready when it has thickened slightly, smells pleasantly tart, and small pockets of whey begin separating at the edges. Over-fermented kefir separates fully into curds and yellowish whey and tastes sharply sour — still safe, just unpleasant.
5. Strain. Pour through the sieve into your second jar, stirring gently with a non-metallic spoon to help the liquid through. The grains stay in the sieve.
6. Repeat. Return the grains to the original jar, add fresh milk, and start again. Refrigerate the finished kefir and drink within about a week.

Troubleshooting common problems

• Kefir won't thicken: the room is too cold, there are too few grains for the volume of milk, or the grains are still recovering from refrigeration. Reduce the milk volume and give it a few cycles.
• Yeasty or beer-like smell: usually over-fermentation or an imbalance towards yeast. Shorten the fermentation and strain more promptly for several batches.
• Slimy or stringy texture: often a temperature issue. It typically resolves with a few cycles at a steadier temperature.
• Pink, orange, black or fuzzy growth: this is mould contamination. Discard the entire batch and the grains, and start fresh. Never attempt to rescue a mouldy culture.

Second fermentation for flavour and fizz

After straining, you can improve flavour with a second ferment. Add fruit, a strip of lemon peel or a little vanilla to the strained kefir, cover loosely and leave at room temperature for a further 6–24 hours before refrigerating. This softens the sourness and increases carbonation. If sealing the bottle to build fizz, release the pressure daily.

Keeping grains alive and taking a break

If you need to pause, place the grains in fresh milk in a sealed container in the fridge. They will ferment very slowly and keep for around two to three weeks, though you should refresh the milk weekly for longer breaks. On returning to room temperature, expect two or three batches before they return to full strength — discard or compost those if the flavour is off.

Food safety when fermenting at home

Milk kefir is a well-established, historically safe fermentation, but a few rules matter:

• Use pasteurised milk. Raw milk fermentation carries additional pathogen risk and is not something I would recommend at home.
• Wash jars and utensils thoroughly in hot soapy water and dry fully before use.
• Trust your senses. Correct kefir smells tart and yeasty. Anything putrid, or any visible mould, means discard.
• Refrigerate the finished drink and consume within roughly a week.
• People who are pregnant, immunosuppressed or seriously unwell should choose commercially produced, quality-controlled kefir rather than home ferments.

How to make water kefir

Water kefir uses a different culture and produces a light, lemonade-like drink suitable for those avoiding dairy.

1. Dissolve 4 tablespoons of sugar in 1 litre of non-chlorinated water and allow to cool to room temperature.
2. Add 3–4 tablespoons of water kefir grains, plus optionally a slice of dried fig or a few sultanas and a slice of lemon to supply minerals.
3. Cover with a breathable cloth and ferment at room temperature for 24–48 hours.
4. Strain out the grains, then bottle the liquid with fruit juice for a 12–24 hour second ferment if you want carbonation. Release pressure daily.
5. Refrigerate and drink within about a week.

Water kefir contains far less protein and calcium than milk kefir and has a much smaller evidence base. Treat it as a pleasant, low-sugar alternative to soft drinks rather than a therapeutic intervention.

How much kefir should you drink?

Clinical trials have typically used between 180 ml and 500 ml daily, with 250 ml twice daily in the H. pylori study and 500 ml daily in the constipation pilot. For general gut health, 150–250 ml a day is a sensible target.

Start smaller. I usually suggest beginning at around 50–100 ml daily for the first week and building up, because a sudden large increase in live microbes commonly causes transient bloating, wind or looser stools. This settles in most people within one to two weeks. If it does not, our articles on probiotic side effects, how long probiotics take to work and trapped wind relief may help.

Timing is less important than consistency. There is no strong evidence that kefir must be taken on an empty stomach; taking it with food may in fact buffer stomach acid and improve microbial survival. See when to take probiotics and whether probiotics survive stomach acid.

Kefir versus probiotic supplements

This is the question I am asked most, and the honest answer is that they do different jobs.

Kefir delivers a broad, undefined mix of many species in a food matrix, along with protein, calcium and B vitamins. Probiotic supplements deliver specific, characterised strains at known doses — which is what clinical trials actually test. The British Dietetic Association makes this point clearly: fermented foods such as kefir contain beneficial microorganisms but are not formally classed as probiotics, because the specific strains and their health effects have not been characterised to the required standard.

In practice: use kefir for general dietary microbial diversity, and a targeted supplement when you have a specific indication and want a strain with trial evidence behind it. For particular conditions, our guides to supplements for IBS, supplements for bloating and supplements for leaky gut set out the strain-level evidence, and how to choose a probiotic explains what to look for on a label. There is no reason the two cannot be used together.

Who should be cautious with kefir

• Immunosuppressed individuals. Anyone on immunosuppressive therapy, undergoing chemotherapy, or with a central venous catheter should discuss live cultures with their medical team before starting. The BDA notes that probiotics may pose a risk where immune function is impaired.
• Cow's milk protein allergy. Fermentation reduces lactose, not milk protein. Milk kefir is not suitable.
• Histamine intolerance. Fermented foods are high in histamine and may worsen symptoms. See our guide to histamine intolerance.
• SIBO. Some people with small intestinal bacterial overgrowth find fermented foods aggravate bloating. Read our SIBO guide before adding kefir.
• Active flares of IBD. Discuss dietary changes with your gastroenterology team — see our Crohn's diet and ulcerative colitis diet guides.
• Low FODMAP diets. Plain kefir is often better tolerated than milk but portion size matters. See the low FODMAP diet.

Kefir contains trace alcohol from yeast fermentation — typically well under 1% and usually around 0.5% or less in commercial products, though home ferments left longer can be higher. This is relevant for anyone avoiding alcohol entirely.

Importantly, kefir does not replace medical assessment. Persistent change in bowel habit, unexplained weight loss, rectal bleeding, difficulty swallowing, vomiting or a family history of bowel cancer all warrant a GP appointment rather than a dietary experiment. Our guide on when to see a GP about stomach symptoms covers the red flags, and bowel cancer screening explains the NHS programme.

How to choose shop-bought kefir in the UK

If home fermenting is not for you, most UK supermarkets now stock kefir. What to look for:

• "Live cultures" on the label. Some products are heat-treated after fermentation, which kills the microbes. If it is shelf-stable at room temperature, it almost certainly contains no live cultures.
• Plain, unsweetened versions. Flavoured kefirs can contain as much added sugar as a yoghurt drink. Check the per-100 ml sugar figure — plain kefir's sugars are residual lactose, not added.
• Made with kefir grains. Some commercial products use a defined starter culture rather than true grains, which yields a narrower microbial profile.
• Short ingredient lists. Milk and cultures is all that is needed.

For comparisons of the wider UK live-culture market, see our reviews of Symprove, Optibac vs Bio-Kult, Yakult vs probiotics and the best probiotic drinks in the UK.

Frequently asked questions about kefir benefits

What are the main benefits of drinking kefir every day?

The best-supported daily benefits are improved lactose digestion, increased gut microbial diversity as part of a fermented-food-rich diet, and a useful contribution of protein, calcium and vitamin B12. Smaller studies suggest possible improvements in bowel regularity and fasting glucose. Effects on blood pressure and inflammatory markers have not been confirmed in pooled randomised trial data.

How long does it take to notice the benefits of kefir?

Digestive changes such as improved regularity are often noticed within one to four weeks. The constipation pilot study ran for four weeks; the Stanford microbiome trial ran for ten. A reasonable trial period is four to eight weeks of consistent daily intake before judging whether it helps you.

Is kefir better than yoghurt?

Kefir typically contains a broader range of microbial species, including yeasts, whereas yoghurt usually relies on two defined bacterial strains. Both improve lactose digestion. Kefir has the edge on microbial variety; yoghurt is often higher in protein per serving depending on the type. Including both is reasonable.

Can you drink kefir if you are lactose intolerant?

Most people with lactose maldigestion tolerate kefir better than milk. A randomised study in adults with lactose maldigestion found kefir improved both lactose digestion and symptoms compared with milk. Start with a small amount. Kefir is not suitable for cow's milk protein allergy, which is a different condition.

How much kefir should I drink per day?

Clinical trials have used 180–500 ml daily. For general gut health, 150–250 ml a day is sensible. Begin with 50–100 ml daily for the first week to reduce the risk of temporary bloating or wind, then build up gradually.

Does kefir help with bloating?

It can go either way. Kefir may reduce bloating over time in people whose symptoms relate to lactose maldigestion or sluggish transit. In the first week or two, however, an increase in live microbes commonly causes temporary bloating and wind. If bloating persists beyond two weeks, kefir may not suit you — this is sometimes the case in SIBO or histamine intolerance.

Is home-made kefir better than shop-bought?

Home-made kefir fermented with live grains generally contains a higher and more diverse live microbe count than pasteurised commercial products, and is far cheaper. Shop-bought kefir offers consistency and quality control, which matters more if you are pregnant, immunosuppressed or unwell. Both are reasonable choices.

Does kefir contain alcohol?

Yes, in trace amounts, because yeasts in the culture produce small quantities of ethanol. Commercial kefir is typically around 0.5% ABV or less. Home ferments left for longer periods, and second-fermented batches, can contain somewhat more. This is worth knowing if you avoid alcohol entirely.

Can you drink kefir on an empty stomach?

Yes, and it is perfectly safe, but there is no strong evidence that this is better. Taking kefir with a meal may buffer stomach acid and improve the survival of live cultures through the stomach. Consistency matters more than timing.

Should I take kefir or a probiotic supplement?

They serve different purposes. Kefir provides broad, undefined microbial variety within a nutritious food. A probiotic supplement provides specific characterised strains at defined doses, which is what clinical trials evaluate for particular conditions such as IBS or antibiotic-associated diarrhoea. If you have a defined problem, a targeted supplement has the better evidence; for general gut health, kefir is an excellent everyday habit. Many people use both.

References

1. Hertzler SR, Clancy SM. Kefir improves lactose digestion and tolerance in adults with lactose maldigestion. Journal of the American Dietetic Association, 2003. View study
2. Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell, 2021. View study
3. Stanford Medicine. Fermented-food diet increases microbiome diversity, decreases inflammatory proteins, study finds, 2021. Read summary
4. Bekar O, Yilmaz Y, Gulten M. Kefir improves the efficacy and tolerability of triple therapy in eradicating Helicobacter pylori. Journal of Medicinal Food, 2011. View study
5. Turan İ, Dedeli Ö, Bor S, İlter T. Effects of a kefir supplement on symptoms, colonic transit, and bowel satisfaction score in patients with chronic constipation: a pilot study. Turkish Journal of Gastroenterology, 2014. View study
6. Salari A, Ghodrat S, Gheflati A, et al. Effect of kefir beverage consumption on glycemic control: a systematic review and meta-analysis of randomized controlled clinical trials. Complementary Therapies in Clinical Practice, 2021. View study
7. Rashidbeygi E, Mehrzad Samarin M, Sheikhhossein F, et al. 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, 2025. View study
8. Rosa DD, Dias MMS, Grześkowiak ŁM, et al. Milk kefir: nutritional, microbiological and health benefits. Nutrition Research Reviews, 2017. View review
9. Kefir as a therapeutic agent in clinical research: a scoping review. Nutrition Research Reviews, 2023. View review
10. The effects of kefir on the human oral and gut microbiome. Nutrients, 2025. View review
11. Nutritional characteristics, health impact and applications of kefir. Foods, 2024. View review
12. Tingirikari JMR, Sharma A, Lee HJ. Kefir: a fermented plethora of symbiotic microbiome and health. Journal of Ethnic Foods, 2024. View review
13. British Dietetic Association. Probiotics and gut health — Food Fact Sheet. Read fact sheet
14. British Dietetic Association. Fermented foods. Read guidance
15. Guts UK Charity. Prebiotics and probiotics. Read guidance
16. National Institutes of Health, Office of Dietary Supplements. Probiotics — Health Professional Fact Sheet. Read fact sheet
17. Harvard T.H. Chan School of Public Health. The Nutrition Source: Probiotics. Read guidance
18. USDA FoodData Central. Kefir composition data. Search database
19. NHS. Irritable bowel syndrome (IBS). Read NHS guidance

About the author

Dr Zeeshan Afzal, MBBS is a practising medical doctor and Clinical Content Lead at Welzo. He writes and medically reviews Welzo's digestive health content, with a focus on translating primary research and UK clinical guidance into practical advice for patients. All Welzo health content is written or reviewed by qualified clinicians and referenced to peer-reviewed literature and recognised UK health bodies.

Medical disclaimer

This article is intended for general information only and does not constitute medical advice, diagnosis or treatment. Kefir and other fermented foods are not a substitute for prescribed medication or medical assessment. If you have persistent digestive symptoms, a diagnosed gastrointestinal condition, a weakened immune system, or you are pregnant or breastfeeding, speak to your GP, pharmacist or a registered dietitian before making significant dietary changes. Seek urgent medical advice for red flag symptoms including unexplained weight loss, rectal bleeding, persistent vomiting, difficulty swallowing or a persistent change in bowel habit.