Kefiran

Kefiran

1. Identity: Chemical Name, Natural Source, and Forms

Chemical Identity

Kefiran is the main exopolysaccharide (EPS) produced by the microflora of kefir grains, being mostly produced by Lactobacillus kefiranofaciens. It is a water-soluble branched glucogalactan heteropolysaccharide with nearly equal amounts of glucose and galactose, possessing numerous beneficial properties including antimicrobial, antioxidant, antitumor, immunomodulatory, and anti-inflammatory properties, as well as antidiabetic, anti-hypercholesterolemic, and antihypertensive effects.

Kefiran has been isolated and purified, and identified as a highly branched heteropolysaccharide, featuring a backbone of glucose and galactose (C4/C3 positions) with 2,6-galactose (C2/C6) as the primary branching point.

The polysaccharide is composed of a hexasaccharide repeating unit and, thus, is known as kefiran. Lactobacillus kefiranofaciens, isolated from kefir grains, produces this extracellular polysaccharide when cultured in appropriate media. The weight-average molecular weight and the z-average radius of gyration of a purified sample were determined to be 7.6 × 10⁵ g/mol and 39.9 nm, respectively, by gel permeation chromatography equipped with a multiangle laser.

Infrared spectroscopy has confirmed that kefiran has a β-configuration, and X-ray photoelectron spectroscopy analysis confirmed the structure and composition of kefiran, revealing a C/O atomic ratio of 1.46. Kefiran has been reported to show an average molecular weight (Mw) of 534 kDa and a number-average molecular weight (Mn) of 357 kDa in some preparations, reflecting variability by source and extraction method.

Infrared spectra of kefiran reveal the presence of carboxyl, hydroxyl, and amide groups, which correspond to a typical heteropolymeric polysaccharide. Scanning electron microscopy images show homogeneous morphology with a porous, sponge-like structure.

The exopolysaccharides present in kefir grains were first discovered and named kefiran by La Rivière et al. (1967).

Natural Source

Kefir grains are initially created by auto-aggregations of Lactobacillus kefiranofaciens and Maudiozyma turicensis or M. humilis, where multiple biofilm producers cause the surfaces to adhere, forming a three-dimensional microcolony. The biofilm is a matrix of heteropolysaccharides called kefiran, which is composed of equal proportions of glucose and galactose.

Kefir grains are white to yellow-white, gelatinous, variable in size (from 0.3–3.5 cm in diameter), and are composed of a microbial symbiotic mixture of lactic acid bacteria (10⁸ CFU/g), yeast (10⁶–10⁷ CFU/g), and acetic acid bacteria (10⁵ CFU/g) that stick to a polysaccharide matrix.

Lactobacillus kefiranofaciens is a non-pathogenic gram-positive bacterium isolated from kefir grains and able to produce the extracellular exopolysaccharide named kefiran. This polysaccharide contains approximately equal amounts of glucose and galactose.

Common Forms and Preparations

The presence of kefir's exopolysaccharides, known as kefiran, which has biological activity, adds value to kefir products. Kefiran can also be used separately in other food products and as a coating film for various food and pharmaceutical products.

Kefiran has been introduced as a biodegradable polymer due to its nontoxicity. This edible biopolymer and its structural derivatives play specific roles in a large number of applications including scaffolds, reserve materials, and encapsulation for drug delivery, owing to its protective features, bifidogenic effects, and antimicrobial activity.

In isolated and purified form, the kefiran exopolysaccharide appears as a white precipitate and can be freeze-dried. In research and industrial contexts, kefiran is obtained either directly from whole kefir, from kefir grain biomass through aqueous extraction and precipitation, or by fermentation of L. kefiranofaciens in optimized culture media. L. kefiranofaciens can produce this extracellular polysaccharide in media containing rice hydrolysate previously degraded by glucoamylase, yielding up to 2.5 g/L after a 7-day culture period at pH 5.0 and 33°C.

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2. Traditional and Historical Use

Geographic and Cultural Origins

For many centuries, milk kefir was a closely guarded secret of the Northern Caucasus region in Russia. The people of the Northern Caucasus region are renowned for their longevity, with one of the highest proportions of centenarians in the world. Milk kefir is a dietary staple in this region.

Kefir has been found in graves in the Bronze Age Xiaohe Cemetery, dating back 3,600 years. The word kefir, which is of North Caucasian origin, became an international word, having originally spread to Russia, Central European, and Eastern European countries at least by 1884.

In the Northern Caucasus region, kefir grains are known by the name "Grains of the Prophet." Their traditional legend holds that the prophet Mohammed gifted kefir grains to the Orthodox Christians in this region. The kefir grains and methods for making kefir were kept secret by people in the Caucasus mountains for many generations. Owning kefir grains was equated with wealth in this region.

Traditional Preparation

Traditionally, kefir was prepared by hanging goatskin bags containing kefir grains and milk near doors. Every time someone passed through, they would shake the bags to ensure that the milk and kefir grains were thoroughly mixed.

Traditional kefir is fermented at ambient temperatures, generally overnight. Fermentation of the lactose yields a sour, carbonated, slightly alcoholic beverage, with a consistency and taste similar to drinkable yogurt.

Today, the gelatinous kefir grains are typically placed in a sterile jar or other nonmetallic container, and milk is poured on top; single-use powdered kefir cultures are also available. The mixture ferments at room temperature for one or two days. Upon completion of fermentation, the kefir is separated from the grains by passing it through a sieve.

Traditional Purposes

Kefir is closely linked to the longevity of the Caucasian people, who were known to live long and healthy lives, with many centenarians among them. Professor Elie Metchnikoff refers to kefir grains in his 1907 book The Prolongation of Life, where he observed that good (or bad) bacteria appear to have a direct effect on health.

Kefiran itself — as a distinct, isolated compound — was not identified or consciously used in traditional practice. Traditional cultures consumed kefiran as an intrinsic, inseparable component of fermented kefir or kefir grain preparations. Its identity as a specific bioactive polysaccharide was only established scientifically in 1967 with its formal characterization. The health properties attributed to traditional kefir consumption — digestive regulation, longevity, immune support, and general vitality — are now understood to be mediated in part by kefiran among other kefir constituents.

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3. Key Constituents and Chemical Composition

Primary Structure

From kefir grains, kefiran was isolated as a water-soluble polysaccharide consisting of approximately equal proportions of galactose and glucose residues. A β-D-(1→6) glucanase from Trichoderma viride was able to fragment the polysaccharide, the main products being equimolar amounts of glucose and a pentasaccharide, kefirose. The variety of linkage types may account for the rather poor accessibility of kefiran to enzymatic attack. This property might be important in the ecology of the kefir grain.

Compositional analysis identifies the main monosaccharide components as galactose (45.36 ± 0.16%) and glucose (47.13 ± 0.06%) in kefiran (KE).

Kefiran is a hydro-soluble prebiotic branched exopolysaccharide that is a hydroxyl-group-rich heteropolysaccharide biopolymer containing glucose and galactose. Kefiran has a molecular weight of around 10⁶ Da.

Producing Organism

Kefiran is a type of water-soluble polysaccharide produced by the lactic acid bacterium Lactobacillus kefiranofaciens (Kandler and Kunath, 1983). While L. kefiranofaciens is the primary producer, other lactic acid bacteria within the grain microbiome also contribute to the polysaccharide matrix of kefir grains.

Physicochemical Properties

Kefiran is stated as the most preferable EPS among fermentation-derived exopolysaccharides due to its water-soluble and biodegradable features. Microbial exopolysaccharides are biothickeners that can be added to a wide variety of food products, where they serve as viscosifying, stabilizing, emulsifying, or gelling agents. Kefiran in particular demonstrates viscoelastic and film-forming properties that make it suitable for both food technology and biomedical applications.

A novel kefir exopolysaccharide (KEPS) derived from kefir grain fermentation was found to have a small molecular weight (12 kDa) compared to the traditionally high molecular weight (12,000 kDa) of kefiran. This illustrates that the EPS fraction of kefir grains is not monolithic; kefiran represents the predominant high-molecular-weight component.

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4. Mechanisms of Action

Immunomodulation

Beyond its structural function, kefiran exhibits antioxidant, antimicrobial, antitumoral, and immunomodulatory activities. Studies have shown that kefiran can protect intestinal epithelial cells from oxidative stress and modulate gut immunity by enhancing IgA secretion and macrophage activation.

Kefiran, a polysaccharide component of kefir, has been shown to increase secretory IgA production in the intestinal mucosa, reinforcing mucosal immunity and providing a first line of defense against enteric pathogens.

Anti-Inflammatory Pathways

The anti-inflammatory effects of kefir and its components are thought to involve multiple pathways of action across various cell types, including the modulation of immune cell signaling, inhibition of NF-κB activation, and regulation of the JAK2 signaling pathway, all of which collectively contribute to the reduction of systemic inflammation.

Both kefiran (KE) and novel kefir exopolysaccharides (KEPS) significantly reduced IL-6 secretion in lipopolysaccharide (LPS)-stimulated macrophages in vitro.

Antihypertensive Mechanism

The antihypertensive activity of kefiran has been attributed to its ability to inhibit angiotensin-converting enzyme (ACE) activity. ACE-inhibitory peptides inhibit the production of the vasoconstrictor angiotensin I and consequently the production of aldosterone, a hormone that stimulates an increase in serum sodium concentration and blood pressure. ACE-inhibitory peptides also inhibit the breakdown of bradykinin, a hormone with vasodilating action, contributing to a decrease in blood pressure.

Prebiotic and Short-Chain Fatty Acid Production

Kefiran exerts strong prebiotic effects primarily as a fermentable substrate that promotes the growth of saccharolytic bacteria. Kefiran fermentation fosters cross-feeding interactions and increases the production of short-chain fatty acids (SCFA), including acetate, propionate, and butyrate. These metabolites promote intestinal homeostasis by serving as energy sources for colonocytes, enhancing tight junction integrity, modulating glucose metabolism, and reducing inflammation.

Butyrate, in particular, plays a central role in strengthening barrier function and regulating epithelial differentiation, which may explain why kefir consumption is consistently associated with increased SCFA-producing bacteria in both human and animal studies.

Antitumor Mechanisms

The main kefir polysaccharide, kefiran, has been identified as responsible for the antitumor properties of kefir. Additionally, kefir contains unique sphingomyelins that promote the secretion of antiproliferative cytokines, particularly IFN-β, in human osteosarcoma cells.

The percent reduction in proliferation by kefir is dose- and time-dependent. Kefir exhibits its antiproliferative effect by downregulating TGF-α and upregulating TGF-β1 mRNA expression. Upon treatment, a marked increase in cell-cycle distribution was noted in the preG1 phase of malignant T-lymphocyte cell lines, indicating a proapoptotic effect.

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5. Scientific Evidence by Area of Use

5.1 Gut Microbiota Modulation and Prebiotic Effects

Exopolysaccharides such as kefiran derived from kefir have been suggested as bioactive compounds due to their potential prebiotic effects and relation to alteration of intestinal microbiota.

Results of analysis of bifidobacteria populations assessed on different sampling sites in a murine model support the use of this exopolysaccharide as a bifidogenic functional ingredient. This animal study demonstrated that oral administration of kefiran specifically promoted the growth of Bifidobacterium species, establishing its bifidogenic (prebiotic) activity. Evidence at this level is animal/preclinical only.

In animal models, kefir supplementation promotes colonization by beneficial species such as Lactobacillus kefiranofaciens and L. plantarum, leading to enhanced SCFA production. SCFAs — particularly acetate and butyrate — are essential for maintaining colonocyte health, regulating inflammation, and stabilizing intestinal pH.

In a parallel-group, randomized, controlled clinical trial, patients with metabolic syndrome were randomized to receive 180 mL/day of kefir (n = 12) or unfermented milk (n = 10) for 12 weeks. Fasting insulin, HOMA-IR, TNF-α, IFN-γ, and systolic and diastolic blood pressure showed a significant decrease by the intervention of kefir (p ≤ 0.05, for each). However, no significant difference was obtained between the kefir and unfermented milk groups (p > 0.05 for each). This result illustrates the challenge of attributing effects specifically to kefiran versus other kefir constituents in clinical settings, and the limited between-group significance is a notable limitation.

Current research indicates that kefir increases beneficial taxa such as Lactobacillus spp., Bifidobacterium spp., and Akkermansia spp., while decreasing pro-inflammatory microbes such as Enterobacteriaceae spp. and Clostridium spp., via antimicrobial metabolite production, competitive exclusion, prebiotic exopolysaccharides, short-chain fatty acid enhancement, immune modulation, and improved gut-barrier integrity.

Evidence strength: Moderate for kefir as a whole product; direct clinical evidence isolating kefiran specifically as the active agent is limited to preclinical and animal studies. No controlled human trials have yet examined isolated kefiran supplementation for gut microbiota outcomes.

5.2 Anti-Inflammatory and Immunomodulatory Effects

Rodrigues et al. evaluated the anti-inflammatory action of kefir in rats using a protocol of oedema and granuloma induction. In this study, water kefir, milk kefir, and kefiran extract inhibited the inflammatory process by 41%, 44%, and 34%, respectively. The treatments also significantly reduced oedema in the animals. The results demonstrate the presence of anti-inflammatory compounds in the symbiotic cultures of kefir.

In murine models of rheumatoid arthritis, kefir supplementation markedly reduced paw swelling (−42%) and pro-inflammatory cytokines TNF-α (−58%) and IL-6 (−45%), indicating robust downregulation of NF-κB and MAPK signaling pathways mediating chronic inflammation.

Exopolysaccharides (EPS), and in particular kefiran, are active against various acute inflammations such as colitis, reducing inflammatory markers such as TNFα and IL-8. They act by modulating pro-inflammatory cytokines and by inhibiting pathways such as NF-κB, which is essential in inflammatory processes. Kefiran has shown significant effects in mouse models of colitis, attenuating weight loss and damage to colonic tissue.

In vitro experiments using human peripheral blood mononuclear cells (PBMCs) showed restoration of T-cell homeostasis through enhanced Treg activity (+31%) and reduced Th17 proliferation (−27%).

Evidence strength: Predominantly preclinical (animal models and cell cultures). Some human in vitro cell data are available. Controlled human trials specifically using isolated kefiran are lacking. Evidence base for kefir-derived immunomodulation in humans is emerging but not yet definitive.

5.3 Antihypertensive and Cardiovascular Effects

The kefir-derived exopolysaccharide kefiran has been demonstrated to reduce systemic cholesterol and blood pressure in spontaneously hypertensive stroke-prone (SHRSP) rats.

Changes in blood pressure and serum components were examined in SHRSP/Hos rats using doses of 100 and 300 mg of kefiran per kg of rat bodyweight. A suppression in the increase in blood pressure was observed in these rats after 30 days. This activity was discussed in terms of the concentration of serum components of the rat, with emphasis on lipid components such as cholesterols, triglycerides, and free fatty acids.

Chronic administration of kefir in a rat model significantly reduced hypertension, along with marked decreases in tachycardia and left ventricular hypertrophy.

Experimental and especially clinical studies that have evaluated the antihypertensive effect of milk kefir are rare in the literature to date. Furthermore, the milk kefir peptides that exhibit the ability to inhibit ACE action have not yet been fully identified.

Kefiran (KE) has been shown to possess antioxidant, blood pressure-lowering, and immune-modulating effects.

Evidence strength: Primarily animal-based (SHRSP rat models). No dedicated human clinical trials isolating kefiran's antihypertensive effect have been published. Cardiovascular benefits are considered preliminary and require clinical validation.

5.4 Antimicrobial and Antifungal Effects

Kefir and its insoluble polysaccharide, kefiran, were both tested for antimicrobial and cicatrizing activities against several bacterial species and Candida albicans using an agar diffusion method. Both kefir and kefiran showed some activity against all organisms tested; the highest activity was against Streptococcus pyogenes.

Kefir grain, kefir suspension, and kefiran were tested for antimicrobial activity against several bacterial and fungal pathogens. The highest activity was revealed against Streptococcus faecalis KR6 and Fusarium graminearum CZ1.

Kefiran is regarded as a striking option over other exopolysaccharides, including alginate, glucans, dextrin, xanthan, and levan, due to its antitumor, antibacterial, antifungal, and immunomodulation activities that have been extensively studied.

Except for a few animal-based studies, most antimicrobial action for kefir was studied using direct growth inhibition assays and has yet to be generalized using in vivo based assays in live tissues post oral administration.

Evidence strength: Predominantly in vitro. Agar diffusion methods and cell culture assays do not translate directly to in vivo clinical efficacy. Clinical antimicrobial evidence for isolated kefiran is absent.

5.5 Antitumor and Antiproliferative Activity

Kefir has been shown to control several cellular types of cancer, such as Sarcoma 180 in mice, Lewis lung carcinoma, and human mammary cancer.

Results indicate that kefir exhibits an antiproliferative and proapoptotic effect in HTLV-1-negative malignant T-lymphocytes. This is consistent with the previously reported antitumor effect of kefir on many types of cancer, such as slowing down Sarcoma 180 growth in mice, inhibition of pulmonary metastasis in Lewis lung carcinoma by orally administered polysaccharide fraction from kefir grains, reduction of proliferation and apoptosis induction in Sarcoma 180 in vitro, as well as the regression of human mammary cancer.

In a murine breast cancer model, two-day cyclical administration of kefir products delayed tumor growth and increased the number of IgA+ cells in the mammary gland. Changes in the balance between CD4+ and CD8+ cells in the mammary gland were observed. Mice receiving cyclic administration showed significant increases in the number of apoptotic cells and decreases in Bcl-2+ cells compared with tumor control groups.

The maximum cytotoxicity recorded after 48-hours treatment with 80 μg/μL kefir was only 42% and 39% in CEM and Jurkat cells, respectively. The percent reduction in proliferation was dose- and time-dependent. Kefir exhibited its antiproliferative effect by downregulating TGF-α and upregulating TGF-β1 mRNA expression.

Evidence strength: Predominantly animal and in vitro studies. While multiple cell lines and animal tumor models show consistent antiproliferative and proapoptotic results, no controlled human clinical trials demonstrating anticancer efficacy for isolated kefiran have been published. Results are considered preliminary and hypothesis-generating for oncology research.

5.6 Wound Healing

Cicatrizing experiments were carried out on Wistar rats with induced skin lesions and Staphylococcus aureus inoculation, using a topical application of a 70% kefir gel. Both kefir and kefiran showed some activity against all organisms tested. Cicatrizing experiments using 70% kefir gel had a protective effect on skin connective tissue, and 7-day treatment enhanced wound healing compared with 5 mg/kg of neomycin-clostebol emulsion.

Many studies have demonstrated the biological activities of kefir, highlighting its potential as an antioxidant, antimicrobial, anti-inflammatory, wound healing, and hypocholesterolemic agent.

Evidence strength: Animal and in vitro only. Topical wound healing applications have not been evaluated in controlled human clinical trials.

5.7 Metabolic Effects: Lipids, Blood Glucose, and Metabolic Syndrome

Preclinical studies conducted in rodent models have shown potential to improve lipid profiles, reduce body weight gain, enhance glucose tolerance, and suppress inflammatory cytokines such as TNF-α and IL-6.

Traditional kefir was found to reduce body weight gain, plasma cholesterol levels, and hepatic triglycerides in mice. In contrast, commercial kefir showed no beneficial effect.

Kefir-derived exopolysaccharides have shown promising effects in experimental rat models of type 2 diabetes mellitus, suggesting potential nutraceutical applications.

To address the global burden of Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD), researchers investigated kefiran as a potential intervention. Kefiran was isolated and purified as a highly branched heteropolysaccharide. In high-fat diet (HFD)-induced MASLD mice, kefiran supplementation ameliorated hepatic injury, lowered inflammation and insulin resistance, suppressed lipogenic protein expression, and thereby alleviated hepatic steatosis.

Additionally, kefiran also restored HFD-induced gut dysbiosis, significantly elevating Parabacteroides, Alistipes, and Alloprevotella, while reducing Lachnoclostridium, Psychrobacter, Allobaculum, and Coriobacteriaceae_UCG-002.

Evidence strength: Predominantly animal data. Human trials examining isolated kefiran's metabolic effects are lacking. Whole-kefir trials in human metabolic syndrome populations show mixed results, often not surpassing the comparison group receiving unfermented milk.

5.8 Anti-Steatotic and Hepatic Effects

In aged, stressed, hypertensive, NASH, and myocardial infarction animal models, kefir restored antioxidant enzyme activities, reduced lipid peroxidation, decreased pro-inflammatory cytokines (IL-6, TNF-α, TGF-β1), and limited fibrosis in liver, kidney, and heart tissues.

Evidence strength: Animal models only. No human hepatic trials with isolated kefiran have been reported.

5.9 Antioxidant Activity

Kefir contains bioactive metabolites including peptides, exopolysaccharides, and organic acids, which enhance its antioxidant, anti-inflammatory, antimicrobial, and hypocholesterolemic effects.

Natural-derived polysaccharides, including kefiran, exert antioxidant effects, attenuating oxidative stress associated with inflammation.

Evidence strength: Primarily in vitro and animal studies. No dedicated randomized controlled trials in humans using isolated kefiran for antioxidant endpoints have been identified in the literature.

5.10 Safety and Feasibility in Critical Illness

An open-label phase I safety and feasibility study examined the safety and feasibility of kefir administration in critically ill patients. Kefir was administered in escalating doses (60 mL, followed by 120 mL after 12 h, then 240 mL daily) to 54 critically ill patients with an intact gastrointestinal tract.

After administering kefir, none of the 54 critically ill patients exhibited signs of kefir-related bacteremia. No side effects like bloating, vomiting, or aspiration were noted, except for diarrhea in two patients concurrently on laxatives.

Evidence strength: This was a single-arm phase I study focused on safety, not efficacy. The absence of adverse events is a meaningful finding but cannot be generalized to all patient populations.

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6. Body Systems and Health Areas of Association

• Gastrointestinal system: The most established health benefits of kefir include gut and digestive health, owing to its rich probiotic diversity, which enhances intestinal balance and lactose digestion. Kefiran contributes through its prebiotic/bifidogenic activity and barrier-strengthening effects.
• Immune system: Kefiran exhibits antioxidant, antimicrobial, antitumoral, and immunomodulatory activities. Mechanisms include enhanced IgA secretion, macrophage activation, and regulation of T-cell subsets.
• Cardiovascular system: Kefir has been linked to cardiovascular and metabolic health benefits including cholesterol-lowering abilities, anti-obesity, angiotensin-converting enzyme inhibitory activity, immunomodulatory characteristics, improved cardiac function, and anti-hypertensive effects. Kefiran specifically contributes to ACE inhibition and cholesterol modulation in animal models.
• Metabolic system: Animal and preliminary data associate kefiran with blood glucose regulation, reduction of hepatic steatosis, and modulation of insulin resistance pathways.
• Integumentary system (skin): Topical kefiran has been studied in animal models for wound healing and anti-infective properties, showing accelerated cicatrization compared to standard antimicrobial preparations.
• Oncology (preclinical): Emerging studies suggest anticancer potential, although further clinical validation is required.
• Musculoskeletal system: Animal models of rheumatoid arthritis show reduction of paw swelling and pro-inflammatory cytokines following kefir supplementation, mediated in part through kefiran's NF-κB inhibitory actions.

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7. Dosage Forms and Dosages Reported in Studies

Forms in Research

Kefiran has been studied in the following forms in published research:

• As an isolated, purified freeze-dried powder (white precipitate), obtained by aqueous extraction from kefir grain biomass followed by ethanol precipitation.
• As an orally administered solution in animal experiments, dissolved in water or buffer.
• As a component of whole kefir beverages in human clinical trials (not as an isolated supplement).
• As a coating film for various food and pharmaceutical products.
• In biomedical research applications including hydrogels and scaffolds for tissue engineering.

Dosages Reported in Animal Studies

Changes in blood pressure and serum components were examined in SHRSP/Hos rats using doses of 100 and 300 mg of kefiran per kg of rat bodyweight. A suppression in the increase in blood pressure was observed in these rats after 30 days.

In one anti-inflammatory mouse study, mice received oral KEPS (100 mg/kg) or kefiran (100 mg/kg) for seven days, followed by LPS or saline injection.

No established human equivalent dosage for isolated kefiran as a dietary supplement has been defined in published clinical literature. Dosages used in human clinical trials have all involved whole kefir beverages rather than isolated kefiran.

Dosages Reported in Human Clinical Studies (Whole Kefir)

In a parallel-group, randomized, controlled clinical trial, patients with metabolic syndrome received 180 mL/day of kefir for 12 weeks.

In an intervention study in women with PCOS, participants consumed 250 mL/day of kefir for 8 weeks.

In an ICU safety study, kefir was administered in escalating doses beginning with 60 mL, followed by 120 mL after 12 hours, then 240 mL daily.

It must be noted that these dosages pertain to whole kefir beverages, not isolated kefiran. The concentration of kefiran in commercial and traditional kefir is variable and is not standardized across products.

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8. Safety Considerations and Interactions

General Safety Profile

Kefiran has been introduced as a biodegradable polymer due to its nontoxicity. Its physicochemical properties and recognized safe status have led to the exploration of kefiran for a range of applications in the food industry and biomedical fields.

While kefir is well recognized for its potential health value as an excellent source of probiotics, some limitations in kefir consumption need to be recognized. These limitations are mostly due to its cholesterol-rich content and potential to trigger allergic reactions.

Immunocompromised Populations

Kefir contains actively growing bacteria and yeast. There is concern that people with a weakened immune system might be more likely to develop infections from these bacteria or yeast. This concern relates primarily to live microorganism content in whole kefir, rather than isolated kefiran polysaccharide.

Kefir, known for its probiotic content, contains cultures of bacteria and yeasts that may pose theoretical risks for immunocompromised individuals. In these patients, a weakened immune system could be less able to control these microorganisms, potentially increasing the risk of fungemia or bacteremia — the presence of fungi or bacteria in the blood.

Although evidence suggests that probiotics are generally safe for people with autoimmune conditions, some case reports have associated probiotic use with serious adverse effects, including an elevated risk of infection. In rare situations, probiotics have been linked to complications such as sepsis, a potentially life-threatening response to infection.

Drug Interactions

Taking kefir along with medications that decrease the immune system might increase the chances of getting sick. Kefir contains live bacteria and yeast. The immune system usually controls bacteria and yeast in the body to prevent infections. Medications that decrease the immune system can increase chances of getting sick from bacteria and yeast.

Patients with diabetes who consume kefir may experience altered blood glucose levels due to the probiotics' effects on insulin sensitivity and glucose metabolism. This interaction can complicate diabetes management and necessitate adjustments in medication dosages to maintain optimal blood glucose control.

The interaction between kefir and the cytochrome P450 enzyme system is complex and can vary depending on the specific strains of probiotics present. Some strains may induce enzyme activity, leading to faster drug metabolism and reduced drug efficacy, while others may inhibit enzyme activity, resulting in slower drug metabolism and increased risk of toxicity.

Safety in Clinical Settings

In the ICU feasibility study, none of the 54 critically ill patients exhibited signs of kefir-related bacteremia. No side effects like bloating, vomiting, or aspiration were noted, except for diarrhea in two patients concurrently on laxatives.

Evidence Gaps and Limitations

Many studies have demonstrated the biological activities of kefir, highlighting its potential as an antioxidant, antimicrobial, anti-inflammatory, wound healing, and hypocholesterolemic agent. Nevertheless, further studies of long-term effects on animal and human models are still needed to prove kefir's efficacy.

Kefir consumption is associated with certain health-enhancing outcomes, including anti-atherosclerotic, anti-inflammatory, antihypertensive, antioxidant, antibacterial, anticancer, and antidiabetic effects. Strong outputs were obtained via antimicrobial, immunomodulatory, anti-inflammatory, and antioxidant effects, supported by extensive experimental evidence. Emerging studies suggest anticancer, antidiabetic, and neuroprotective potentials, although further clinical validation is required.

A critical limitation across all kefiran research is the paucity of human clinical trials specifically studying isolated kefiran as a defined intervention. The overwhelming majority of evidence derives from animal models, in vitro cell culture experiments, or whole-kefir human trials where kefiran's individual contribution cannot be separated from the contributions of live probiotic organisms, bioactive peptides, organic acids, and other kefir constituents. Until well-designed, adequately powered randomized controlled trials using characterized kefiran preparations are conducted in humans, the translation of preclinical findings to clinical recommendations remains speculative.

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