Kefir is a drink made by the fermentation of kefir grains in milk or water. Not only is kefir a powerful probiotic as it contains yeasts and bacteria, but it may also boost the immune system, fight cancer, and improve gut health. Keep reading to learn more about the health benefits and side effects of kefir.
What Is Kefir?
Kefir is a fermented beverage made from kefir grains, originally from the Caucasus mountains between Asia and Europe. The word “kefir” originates from the Turkish word “keyif”, which means “feeling good” .
Kefir grains contain several species of bacteria and yeasts. They are small, yellowish-white in color with the appearance of miniature cauliflowers .
Kefir is best known as a probiotic, which helps digestion .
However, this drink has a variety of other benefits, including:
- Boosting immunity and gut health [4, 5, 6, 7, 8]
- Improving digestion [9, 6]
- Combating allergies [10, 11, 12]
- Fighting cancer [13, 14]
- Killing bacteria and fungi [15, 16]
- Preventing obesity [17, 18, 19]
- Improving heart function [20, 21, 22, 23]
- Boosting bone health 
- Helping with diabetes 
- Improving skin health [26, 27]
How To Make Kefir?
It is fairly easy to make milk kefir at home by following the steps below :
- Choose the type of milk you want- cow, goat, buffalo, sheep, donkey, soy. The fermentation time and temperature may vary on the type of milk used.
- Place a tablespoon of milk kefir grains in a medium glass jar.
- Add 2 cups of milk in the jar and cover it with a towel or a cloth, but do not fully close it with a lid.
- Place the jar at room temperature to ferment for 24-36 hours. During the fermentation process, the bacteria and yeasts in kefir break down the glucose and sugar into amino acids, lactic acids, and other substances.
- Use a strainer to separate the kefir grains from the milk kefir.
- The milk kefir is safe and ready to drink. Either you drink it directly or you can store it in your fridge (at 4°C) for later consumption.
Drinking the milk kefir after it’s been refrigerated reduces the lactose content, which is better for people with lactose intolerance and diabetes.
The kefir grains can either be stored in the fridge for later use or can be used directly to make more milk kefir.
Kefir’s taste depends on the milk used, but it is usually slightly sour, refreshing, and creamy.
The nutritional value of kefir varies depending on the milk or water used, kefir grains, and the way it is produced and stored. A cup of low-fat milk kefir is around 110 calories.
- Proteins (3%-6.4%)
- Carbohydrates (3.8%–4.7%)
- Fats (0.2%-2.3%)
- Alcohol (0.48%)
Kefir grains may contain a variety of bacteria, including:
- Lactobacillus species (paracasei, parabuchneri, casei, kefiri, delbrueckii , plantarum, fermentum, acidophilus, rhamnosus, fructivorans, hilgardii, satsumensis, uvarium, brevis, helveticus) [37, 4, 36, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50]
- Acetobacter species (syzygii, fabarium, orientalis, lovaniensis, aceti, rasens) [42, 28, 37, 51, 46, 47, 48]
- Lactococcus species (lactis, cremoris) [37, 4, 36, 39, 52, 41, 43, 47, 48, 50]
- Leuconostoc species (mesenteroides, citreum) [4, 36, 41, 28, 46, 48, 49, 50]
- Streptococcus species (thermophilus, durans) [4, 39, 52, 53, 47]
- Bifidobacterium (bifidum, aquakefiri, psychraerophilum) [45, 51, 46]
- Enterococcus faecalis 
- Gluconobacter japonicus 
The yeasts in kefir grains are:
- Saccharomyces species (cerevisiae, unisporus, rouxii, turicensis) [36, 37, 54, 43, 51, 46, 47, 48, 49, 55]
- Candida species (kefyr, lipolitica, holmii, crusei, lambica, inconspicua, maris) [36, 41, 43, 47]
- Kluyveromyces species (lactis, marxianus, matxianus) [37, 54, 43, 45, 48, 55]
- Lachancea species (meyersii, fermentati) [56, 28, 46, 48, 49]
- Kazachstania species (aerobia, unispora, servazzii, solicola) [37, 47, 48]
- Hanseniaspora species (valbyensis, uvarum, guillermondi) [46, 47, 49]
- Pichia species (membranifaciens, kudriavzevii, fermentans) [49, 57]
- Zygosaccharomyces species [36, 41]
- Debaryomyces hansenii 
- Torulaspora delbrueckii 
- Geotrichum candidum 
- Vitamins: vitamin A, vitamin B1, vitamin B2, vitamin B5, vitamin B6, vitamin B7, vitamin B9, vitamin C, vitamin K, vitamin B12
- Amino acids: valine, isoleucine, methionine, lysine, phenylalanine, tryptophan, threonine
- Minerals: potassium, calcium, phosphorus, magnesium, iron, zinc, copper, manganese
Mechanisms of Action
Kefir boosts the immune system by:
- Activating large white blood cells (macrophages) [4, 60].
- Increasing the breakdown of bacteria and other harmful microorganisms (phagocytosis) .
- Boosting nitric oxide (NO) and cytokine production to decrease Th2 dominance (shifting the immune response to Th1 by decreasing IL-8 and increasing IL-5) [4, 60].
Kefir improves gut health by:
- Increasing beneficial bacteria, yeast, and other microorganisms in the gut, including Lactobacillus, Lactococcus, and Bifidobacterium [61, 8].
- Decreasing harmful bacteria, yeast and other microorganisms in the gut, such as Enterobacteriaceae and Clostridium .
Kefir helps fight cancer by:
- Reducing the release of growth factors of cancer (TGF-α, TGF-β, and Bcl2), while increasing a protein that triggers cell death (Bax), resulting in cancer cell death .
- Increasing the release of interferon-β, a cytokine which blocks the growth of cancer cells .
- Increasing the level of an enzyme that prevents DNA damage (glutathione peroxidase) and decreasing a chemical that causes DNA damage (malondialdehyde) [63, 64].
Kefir improves digestion as:
- Lactose is lower in kefir compared to milk, hence it is easily digested by people with lactose intolerance .
Kefir prevents obesity by:
- Decreasing the levels of an enzyme that makes fats (fatty acid synthase), while increasing the levels of an enzyme that blocks fat production (p-acetyl-CoA carboxylase) .
- Activating multiple pathways that block the production of new fats (such as AMPK and SREBP-1c) .
- Increasing the release of proteins that break down fats (such as PPAR alpha) [65, 18].
Kefir fights allergies by:
- Preventing an allergic response (reducing immunoglobulin E (IgE) antibody production) .
- Reversing Th2 dominance, by increasing the cytokines produced by Th1 cells, while decreasing the cytokines produced by Th2 cells .
Health Benefits of Kefir
1) Kefir Boosts Immune Function
In mice, kefir boosted protective immunity and increased resistance to gut infections. It increased the number of cells with immunoglobulin A (IgA) antibodies in the small and large intestine, as well as the number of cells with IL-4, IL-10, IFN-γ, and IL-6 in the small intestine [68, 69, 70].
2) Kefir Enhances Gut Health
In a study (DB-RCT) on 82 patients, kefir and triple antibiotic therapy (amoxicillin, clarithromycin, and lansoprazole) were more effective in killing Helicobacter pylori, which causes stomach infections and ulcers, than the antibiotics alone .
In 76 children with gut infections, bifidokefir (kefir containing Bifidobacterium bifidum) restored the gut bifidobacteria in 73.4% and lactobacilli in 82% of patients to their normal levels within 7 days .
Kefir prevented the growth of Campylobacter jejuni in chicks, one of the most common causes of food poisoning .
Kefir protected mice against a gut infection caused by the parasite, Giardia intestinalis .
In mice, kefir reduced gut inflammation by increasing immune defense (boosting immunoglobulin A antibodies) and reducing inflammation (by increasing IL-10 and decreasing IFN-γ and IL-1β). Thus, it could be used to combat gut infections [74, 75].
In fact, the bacteria and yeasts in kefir stopped bacterial growth that causes gut infections, including Escherichia coli, Salmonella, and Bacillus cereus .
A complex sugar (polysaccharide) produced by a bacteria in kefir decreased nitrogen oxides (high levels can cause gut issues), and increased free fatty-acids (control cytokine production), improving the gut microbiota. Tibetan kefir grains also contain Lactobacillus plantarum and acts as an antioxidant in cells [77, 78, 79, 38].
One major issue with probiotics is that the stomach acid kills some strains before they can reach the intestines, rendering them inactive. But the probiotics from kefir were able to survive in a stomach-like acidic environment .
3) Kefir Improves Digestion
In a pilot study on 20 adults with constipation, kefir increased the frequency and consistency of stools, reduced the use of laxatives, and improved bowel movements when consumed for 4 weeks .
In 42 adults with mental and physical disabilities, 2g of kefir (lyophilized) for 12 weeks provided complete relief from constipation in 9 participants and reduced symptoms in most. Kefir could be used as a safe remedy to prevent constipation .
Kefir can also increase digestive enzymes. It helped to break down and digest proteins in rats .
4) Kefir Helps with Lactose Intolerance
In a study (randomized block design) of 15 adults with lactose intolerance, kefir improved lactose digestion and tolerance as well as yogurt. It also reduced bloating and stomach pain. Raspberry-flavored kefir has a weaker effect than the unflavored kefir .
A beverage made of eggshell and milk kefir had less lactose and more calcium than regular milk. Thus, milk kefir could be easier to digest by lactose intolerant people – both because of the lower lactose content and the beneficial probiotics .
5) Kefir Aids Weight Loss
In an 8-week study (RCT) on 75 obese or overweight women, kefir reduced the weight, body mass index (BMI), and waist size. Low-fat milk also led to similar results .
Kefir peptides decreased fat accumulation and increased breakdown of fatty acids in obese rats. Complex sugars (polysaccharides) from kefir also decreased body weight, body fat, and cholesterol (VLDL) blood levels in obese rats [65, 83].
In mice with the non-alcoholic fatty liver disease, kefir peptides reduced body weight by decreasing fat storage and increasing fat break-down .
6) Kefir May Protect the Heart and Blood Vessels
Kefir reduced the blood levels of total cholesterol, cholesterol (LDL), and triglycerides in an 8 -week study (RCT) on 75 obese or overweight women. Soy-goat milk kefir also raised HDL cholesterol in rats. These effects lower the risk of heart disease [20, 84].
However, kefir did not lower cholesterol or triglyceride levels in 13 men with high cholesterol levels in a 4-week study (SB-RCT) .
Kefir decreased blood pressure levels, high heart rate (tachycardia), and heart enlargement (cardiac hypertrophy) in rats with high blood pressure. Kefiran, a complex sugar extract from kefir, also decreased blood pressure in rats with high blood pressure [86, 21, 22, 23].
7) Kefir Boosts Bone Health
8) Kefir Helps With Diabetes
In one study on mice with diabetes, a combination of soy and goat milk kefir reduced blood glucose levels and increased antioxidant enzymes (glutathione). In fact, the combination has a stronger effect than kefir made just from soy or goat milk. Goat milk-soy kefir may also increase the activity of the pancreas to improve glucose control .
9) Kefir May Reduce Tooth Decay
10) Kefir Helps Fight Cancer
Milk kefir delayed tumor growth and decreased tumor size of breast cancer in mice. Water kefir also blocked tumor growth and increased immune cells that kill cancer (T helper and cytotoxic T cells) in mice with breast cancer. It also stopped tumor growth in other mice studies [93, 94, 95, 74, 96, 97, 98].
In rats, milk kefir prevents stomach ulcers caused by radiotherapy .
11) Kefir May Reduce Inflammation
In mice with high cholesterol, kefir reduced inflammatory compounds (IL-6, TNF-α) and increased the anti-inflammatory ones (IL-10) .
12) Kefir May Improve Skin Health and Reduce Scars
Kefir gel reduced wound size and scar tissue in rats with burn wounds .
A 70% kefir gel sped up the wound healing and protected the skin connective tissue in rats infected with the bacteria Staphylococcus aureus. This bacteria is one of the most common causes of skin infections .
13) Kefir May Fight Allergies
Kefir extract (kefiran) reduced airway inflammation in mice with asthma. It reduced the production of allergy-causing antibodies (immunoglobulin E, IgE) and inflammatory compounds (cytokines IL-4, IL-5, IL-13) [10, 11, 12].
In mice, Lactobacillus kefiranofaciens bacteria in kefir decreased IgE production, pointing to its allergy-reducing effects .
In fact, the effects of Kefir on reducing inflammation and boosting gut immunity cannot be isolated from its ability to combat allergies. Kefir shifts the immune response from Th2- to Th1-dominant, which is key in reducing allergic response .
14) Kefir Kills Harmful Bacteria And Fungi
Microorganisms in kefir grains stop the growth of the following bacteria:
- Salmonella species (enteritidis, typhimurium), which causes food poisoning [108, 109, 110, 111, 76, 112, 113, 114].
- Escherichia coli, which causes Urinary Tract Infections (UTIs), diarrhea, and inflammatory bowel disease [115, 116, 117, 110, 111, 76, 118, 113, 119].
- Listeria species (monocytogenes, innocua), which can cause many serious infections affecting the brain, bones, joints, chest, and heart [108, 116, 117, 110, 111].
- Bacillus species (cereus, subtilis), which can cause food poisoning [108, 16, 15, 111, 76, 118].
- Staphylococcus aureus, a bacteria resistant to many antibiotics, which commonly causes skin and respiratory infections and food poisoning [108, 16, 15, 111, 5, 118, 113, 119].
- Pseudomonas aeruginosa, a bacteria resistant to most antibiotics that can cause life-threatening drug-resistant infections [108, 16, 111, 118, 26].
- Enterococcus faecalis, one of the leading causes of hospital-acquired infections [108, 111, 118].
- Streptococcus species (pyogenes, agalactiae), which can cause strep throat, tonsillitis, scarlet fever, and infections in newborns [5, 5, 120].
- Klebsiella pneumoniae, which may cause respiratory infections such as bronchitis and pneumonia [16, 118].
- Shigella (sonnei, flexneri), which causes food poisoning [108, 110, 113].
- Yersinia enterocolitica, which causes a gut infection [116, 110].
- Cronobacter sakazakii, which can cause frequently lethal infections in infants, and UTIs and wound infections in adults [111, 121].
- Helicobacter pylori, which causes stomach infections [71, 122].
Kefir vs. Yogurt
Although both kefir and yogurt are probiotics with many health benefits, there are some differences and similarities between them.
Yogurt contains bacteria (Eubacteria, Lactobacillus, and Bifidobacteria) and yeasts (Debaryomyces hansenii, Kluyveromyces marxianus, Yarrowia lipolytica, Issatchenkia orientalis). But, kefir contains more species of bacteria and yeast than yogurt, making it a more broader-spectrum probiotic [123, 124].
Yogurt improved memory and brain function in men. No studies have yet examined the effects of kefir on the brain, except for one study in which kefir improved sleep in chemotherapy patients [132, 106].
Kefir consumption may cause :
However, most participants did not report any side effects .
Make sure your kefir is adequately fermented before you consume it. Although well-fermented milk kefir reduces lactose intolerance, you may wish to avoid dairy kefir altogether if you are lactose intolerant. Rather, you can choose kefir made from soy, coconut, or other non-dairy sources .
Limitations and Caveats
Most studies investigating the benefits of kefir are performed on animals and cells, while the human studies included a small number of participants.
More human studies are needed to confirm its effectiveness.
Although kefir contains some bacteria that are resistant to antibiotics (especially kanamycin and tetracycline), antibiotics (especially taken orally) may still kill some of the bacteria in kefir. This would reduce the beneficial effects of kefir. The yeast in kefir is not affected by the antibiotics [133, 134, 135].
Since kefir balances the immune response, it should be used cautiously with immunosuppressive drugs, including :
- Biologic drugs like Muromonab-CD3 or Basiliximab
Although kefir may help balance the gut microbiome during chemotherapy, it should be taken cautiously. Some lactic acid bacteria and bifidobacteria in kefir are resistant to chemotherapy drugs. Other strains in Kefir may be killed by chemotherapy [137, 138, 139].
Kefir may contain small amounts of alcohol (0.5%, similar to non-alcoholic beer). People who take Disulfiram for alcohol dependence may want to avoid it. Concurrent use could cause adverse effects, such as nausea, vomiting, headaches, and heart problems .
When kefir drinks are prepared industrially, the fermentation processes are generally safe with a very low risk of contamination .
It is recommended to initially consume 100 mL of kefir and then increase the amount once your body adjusts to drinking it.
Kefir is popular and well-tolerated among cancer survivors.
Most users report improved gut health, digestion, reduced constipation, better mood, and health in general.
People with lactose intolerance and acid reflux disorders (Gastroesophageal reflux disease, GERD) experienced benefits with kefir consumption.
Users also experienced a decrease in blood pressure, pain, migraines, and flu/colds.
However, some users reported side effects such as infections, rash, constipation, sore throat, and nausea when using kefir.
One user felt that kefir did not help with his lactose intolerance.