Kefir is a probiotic drink made by the fermentation of milk or water with kefir grains containing yeasts and bacteria. It may help modulate the gut flora and relieve constipation. Read on to learn more.
What Is Kefir?
Kefir is a fermented beverage made with milk and kefir grains, originally from the Caucasus mountains between Asia and Europe. The word “kefir” originates from the Turkish word “keyif,” which means “feeling good” [1].
Kefir grains contain several species of bacteria and yeasts. They are small, yellowish-white in color with the appearance of miniature cauliflowers [2].
Kefir is best known as a probiotic, which helps digestion [3].
However, kefir is under investigation for a number of other potential 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 [24]
- Helping with diabetes [25]
- Improving skin health [26, 27]
How To Make Kefir?
Traditionally, kefir is made by adding kefir grains (which contain microbial cultures) to cow’s milk. It is also made by using other types of milk, such as goat, sheep, donkey, soy, rice, or coconut [13, 28].
Water kefir is a probiotic drink containing water and kefir grains, similar to kombucha and ginger beer, whereas coconut kefir is prepared from coconut water and kefir grains [29, 28].
It is fairly easy to make milk kefir at home by following the steps below [30]:
- Choose the type of milk you want: cow, goat, buffalo, sheep, donkey, or 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.
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 and creamy.
Nutrition Facts
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.
Milk kefir contains [30, 31, 32, 33, 34, 35]:
- Proteins (3% – 6.4%)
- Carbohydrates (3.8% – 4.7%)
- Fats (0.2% – 2.3%)
- Alcohol (0.48%)
Components
Since kefir grains come in different varieties, their components may vary from country to country and from grain to grain. Kefir can contain numerous probiotic bacteria and yeasts [36, 3].
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 [39]
- Gluconobacter japonicus [42]
The yeasts in kefir grains may include:
- 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 [54]
- Torulaspora delbrueckii [54]
- Geotrichum candidum [44]
Kefir also contains [31, 58, 59]:
- 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
How It Works
Researchers have investigated the effect of kefir and its probiotic bacteria in cell studies. They have observed a number of effects on the immune system, gut flora, and fat metabolism.
Kefir’s immune-modulating effects include:
- Activating large white blood cells (macrophages) [4, 60].
- Increasing the breakdown of bacteria and other harmful microorganisms (phagocytosis) [4].
- 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].
- Preventing an allergic response (reducing immunoglobulin E (IgE) antibody production) [61].
- Reducing Th2 dominance, by increasing the cytokines produced by Th1 cells, while decreasing the cytokines produced by Th2 cells [61].
Kefir’s effects on gut bacteria include:
- Increasing beneficial bacteria, yeast, and other microorganisms in the gut, including Lactobacillus, Lactococcus, and Bifidobacterium [62, 8].
- Decreasing harmful bacteria, yeast and other microorganisms in the gut, such as Enterobacteriaceae and Clostridium [62].
Kefir’s effects on weight and metabolism include:
- 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) [63].
- Activating multiple pathways that block the production of new fats (such as AMPK and SREBP-1c) [64].
- Increasing the release of proteins that break down fats (such as PPAR alpha) [63, 18].
Potential Benefits of Kefir
Kefir is considered very safe for most people to consume as food, but it has not been approved for any health purpose or medical claim. If your immune system is compromised for any reason, talk to your doctor before drinking kefir.
Possibly Effective For
1) Gut Flora
In a study 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 [65].
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 [7].
In mice, kefir increased the number of bacteria that are beneficial for gut health (lactic acid bacteria). It also reduced harmful bacteria (Enterobacteriaceae and Clostridia) [62].
Kefir prevented the growth of Campylobacter jejuni in chicks, one of the most common causes of food poisoning [66].
Kefir protected mice against a gut infection caused by the parasite, Giardia intestinalis [67].
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 [68, 69].
In fact, the bacteria and yeasts in kefir stopped bacterial growth that causes gut infections, including Escherichia coli, Salmonella, and Bacillus cereus [70].
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 [71, 72, 73, 38].
One major issue with probiotics is that 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 [38].
2) Constipation
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 [6].
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 [74].
Kefir can also increase digestive enzymes. It helped to break down and digest proteins in rats [75].
Insufficient Evidence For
The following purported benefits are only supported by limited, low-quality clinical studies. There is insufficient evidence to support the use of kefir for any of the below-listed uses. Kefir is considered very safe for the majority of people, but it should never be used to replace something your doctor recommends or prescribes.
3) Immune Function
In 18 healthy adults, 6-week kefir consumption reduced blood IL-8 (a chemokine) levels and raised IL-5 levels. This results in increased gut immune function [4].
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 [76, 77, 78].
4) Lactose Intolerance
In a study of 15 adults with lactose intolerance, kefir improved lactose digestion and tolerance as well as yogurt did. It also reduced bloating and stomach pain. Raspberry-flavored kefir has a weaker effect than the unflavored kefir [9].
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 [79].
The fermentation process in milk kefir decreases the lactose content in the milk, which makes it easier to digest. Kefir made with soy or coconut milk, or even water, is lactose-free [30, 28, 13].
5) Weight Management
In an 8-week study 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 [17].
In obese mice, kefir reduced body weight, body fat, liver weight, total cholesterol, triglycerides, and LDL cholesterol, thus preventing obesity and non-alcoholic fatty liver disease [18, 19].
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 [63, 80].
In mice with the non-alcoholic fatty liver disease, kefir peptides reduced body weight by decreasing fat storage and increasing fat break-down [64].
6) Heart Health
Kefir reduced the blood levels of total cholesterol, cholesterol (LDL), and triglycerides in an 8-week study on 75 obese or overweight women. Soy-goat milk kefir also raised HDL cholesterol in rats [20, 81].
However, kefir did not lower cholesterol or triglyceride levels in 13 men with high cholesterol levels in a 4-week study [82].
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 [83, 21, 22, 23].
In mice with high cholesterol, kefir decreased fat buildup in the arteries. This reduces the risk of clogged, hardened arteries (atherosclerosis) [84].
In mice with non-alcoholic fatty liver disease, kefir reduced body weight, blood levels of triglycerides, cholesterol, and free fatty acids, reducing the risk for heart diseases [64, 85].
7) Bone Health
In a 6-month pilot study, kefir consumption increased the hip bone density, the blood levels of parathyroid hormone (PTH), and calcium in 40 patients with osteoporosis [24].
Kefir consumption for 12 weeks increased bone mineral density and thickness in rats with osteoporosis [86].
8) Diabetes
In a study of 60 patients with type 2 diabetes, milk kefir decreased hemoglobin A1c (HbA1C), and glucose blood levels. Hence, it could be added to the diet to help with diabetes [25].
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 [87].
9) Tooth Decay
In 22 healthy adults, kefir blocked the growth of Streptococcus mutans, a bacteria that causes tooth decay, as effectively as the typical fluoride rinse [88, 89].
Animal & Cell Research (Lacking Evidence)
No clinical evidence supports the use of kefir for any of the conditions listed in this section. Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.
10) Inflammation
Kefir decreased the production of inflammatory compounds (IL-6, TNF-α, IL-1β, and TGF-β) in obese rats, reducing inflammation and DNA damage [18, 63].
In mice with high cholesterol, kefir reduced inflammatory compounds (IL-6, TNF-α) and increased the anti-inflammatory ones (IL-10) [84].
Kefir peptides reduced the inflammatory compounds (TNF-α, IL-6, and IL-1β), which were elevated in mice with non-alcoholic fatty liver disease [64].
11) Skin Health and Scars
Kefir gel reduced wound size and scar tissue in rats with burn wounds [26].
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 [5].
Milk kefir also protected cells from UV damage. Aside from preventing skin cancer, this may reduce skin aging [27, 90].
12) 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 [61].
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 [4].
13) Antimicrobial Activity
Microorganisms in kefir grains stop the growth of the following bacteria:
- Salmonella species (enteritidis, typhimurium), which causes food poisoning [91, 92, 93, 94, 70, 95, 96, 97].
- Escherichia coli, which causes Urinary Tract Infections (UTIs), diarrhea, and inflammatory bowel disease [98, 99, 100, 93, 94, 70, 101, 96, 102].
- Listeria species (monocytogenes, innocua), which can cause many serious infections affecting the brain, bones, joints, chest, and heart [91, 99, 100, 93, 94].
- Bacillus species (cereus, subtilis), which can cause food poisoning [91, 16, 15, 94, 70, 101].
- Staphylococcus aureus, a bacteria resistant to many antibiotics, which commonly causes skin and respiratory infections and food poisoning [91, 16, 15, 94, 5, 101, 96, 102].
- Pseudomonas aeruginosa, a bacteria resistant to most antibiotics that can cause life-threatening drug-resistant infections [91, 16, 94, 101, 26].
- Enterococcus faecalis, one of the leading causes of hospital-acquired infections [91, 94, 101].
- Streptococcus species (pyogenes, agalactiae), which can cause strep throat, tonsillitis, scarlet fever, and infections in newborns [5, 103].
- Klebsiella pneumoniae, which may cause respiratory infections such as bronchitis and pneumonia [16, 101].
- Shigella (sonnei, flexneri), which causes food poisoning [91, 93, 96].
- Yersinia enterocolitica, which causes a gut infection [99, 93].
- Cronobacter sakazakii, which can cause frequently lethal infections in infants, and UTIs and wound infections in adults [94, 104].
- Helicobacter pylori, which causes stomach infections [65, 105].
Microorganisms in kefir grains kill fungi, including Candida, Saccharomyces, Rhodotorula, Torulopsis, Microsporum, and Trichophyton species [15, 5, 96].
Cancer Research
In one clinical study of 40 patients with colorectal cancer undergoing chemotherapy, kefir reduced sleep difficulties. However, it didn’t reduce gut complaints [106].
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 [107, 108, 109, 68, 110, 111, 112].
In rats, milk kefir prevents stomach ulcers caused by radiotherapy [113].
In multiple cell studies, milk kefir blocked tumor growth and caused cancer cell death in leukemia, colorectal cancer, stomach cancer, and breast cancer [114, 115, 116, 117, 118, 119, 120].
Milk kefir protects cells from UV damage, which causes skin cancer [27].
Kefir’s effects on cancer cells in the lab include:
- 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 [13].
- Increasing the release of interferon-β, a cytokine which blocks the growth of cancer cells [121].
- Increasing the level of an enzyme that prevents DNA damage (glutathione peroxidase) and decreasing a chemical that causes DNA damage (malondialdehyde) [118, 122].
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.
Kefir vs. Yogurt
Although both kefir and yogurt are probiotics with many health benefits, there are some differences and similarities between them.
Components
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].
Health Benefits
More studies have investigated the potential benefits of yogurt than kefir for bone health [125, 126].
Both kefir and yogurt have produced benefits in heart disease and diabetes [127, 128, 129].
Although yogurt is beneficial for gut health and the immune system, kefir has been more effective in improving gut microbiota, fighting infections, and boosting immune function [130, 131].
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].
Side Effects & Precautions
Kefir consumption may cause [9]:
- Diarrhea
- Stomach pain
However, most participants did not report any side effects [4].
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 [79].
Drugs Interactions
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 [136]:
- Azathioprine
- Cyclosporine
- Biologic drugs like Muromonab-CD3 or Basiliximab
- Mycophenolate
- Tacrolimus
- Sirolimus
- Corticosteroids
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 [140].
Safety Considerations
When kefir drinks are prepared industrially, the fermentation processes are generally safe with a very low risk of contamination [141].
Too much washing or improper processing can change the microbiota of the kefir grains and cause contamination by harmful bacterial species (Bacillus or Micrococcus) [142, 143].
Supplementation
Dosage
Based on clinical trials, kefir is safely consumed at a daily dose of 200-600 mL [24, 4, 25, 6].
If you aren’t used to consuming fermented foods and drinks, you may want to start with a small amount (about 100 mL) and then increase the amount once your body adjusts to drinking it.
User Experiences
Many kefir drinkers 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.
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.
