Updated: Mar 22
I hope you all enjoyed the introduction to the history of kefir last month, in this article I will dive deeper into the scientific evidence that kefir is good for you. I will try to limit the science lingo and make this as digestible (pun intended!) as possible, and explain how kefir can give you a healthier gut microbiome, support your metabolism, and fortify your immune system.
To recap, the kefir we make at Nettlebed Creamery is made from whole milk and with traditional kefir grains; it is essentially fermented milk and is full of thousands of different species of bacteria and yeasts which are thought to have probiotic properties, and therefore drinking it should be beneficial to your health. The use of traditional grains is what differentiates our kefir from other brands you can buy at the supermarket which tend to be made with dried pure starter cultures instead; kefir made with grains contains a much more varied and diverse combination of microbes which can go further to improve your health. It can be drunk by anyone of all ages but might be particularly beneficial to those who are recovering from an illness that required a bout of antibiotics, those with IBS, or if you are diabetic, amongst other things. The reasons why will be explored in the following paragraphs.
One of the first things we look for when investigating the effects of a probiotic is whether it can alter the existing gut microbiome. One research group explored this by feeding kefir to mice, and while they found no difference in the amount of bacteria in the guts of these mice, they did find a difference in the type of bacteria that were there (1). The populations of the groups of bacteria Bacteroidetes, Lactobacillus and Lactococcus increased, whereas the populations of Firmicutes and Proteobacteria decreased; as usual, these names are all a bit of a mouthful and we’ll ignore the use of italics for some and not others, but what this finding boils down to is a shift to what is considered a “healthier” microbiome. Similar results were found in a study in which dogs were fed kefir (results did not show how palatable the dogs found it, but maybe this is a study you could do at home!) (2).
In a study conducted with people with metabolic syndrome (a combination of diabetes, high blood pressure, and obesity), small changes were seen in the composition of the microbiome, but when tested further they found that parameters associated with metabolic syndrome had improved; for example reduced blood pressure and decreased fasting insulin levels (3). It is important when looking at results like these to take them with a pinch of salt, as the microbiome can be changed by lots of different things (genetics, illness, what someone ate recently, etc), and understanding about how this works is still a work in progress. However, these studies show promising results.
Obesity is often something investigated in gut microbiome studies, as research has shown quite a strong link between the two. Dysbiosis (an imbalance in the microbiome) in childhood caused by, for example, use of antibiotic, is linked to a higher risk of obesity in adulthood (4), and scientists have established distinct “obese microbiome” and “lean microbiome” profiles, with certain types of bacteria being more prevalent in one over the other (5). Several studies have looked into how kefir can alter this interaction, all of which finding that consumption of kefir (usually in mice or rats on a high fat diet) reduces weight gain (or increases weight loss, depending on the study) and also reduces cholesterol. This is thought to be due to reduction of fat breakdown in the gut by some of the components in kefir (6–8). Via a potentially similar mechanism, kefir can also help treat diabetes, which is another condition closely linked with the gut microbiome and especially with dysbiosis in childhood (4). In various studies both people and mice fed kefir showed reduced insulin resistance, inflammation, and fasting glucose levels, as well as other parameters indicating improved health for diabetics (9,10).
You might have heard that kefir, among other probiotics and fermented foods, is good for your immune system. I won’t go into too much detail here, as the immune system is incredibly complicated, but this is true due to a number of different actions from kefir. It has antimicrobial activity against pathogenic bacteria, boosts certain components of your immune system, allowing it to defend you against viruses and infection, and it is also anti-inflammatory and can therefore help with inflammatory bowel disease (11).
Kefir can directly regulate the mucosal immune system in the gut – this is the body’s first line of defence against viruses and disease-causing bacteria (you also have extensions of the mucosal immune system in your lungs and urogenital tract which do the same thing) by preventing them from getting into the bloodstream. In the gut, kefir has direct anti-microbial effects on many pathogenic bacteria, inhibiting the growth of the bacteria that give you Salmonella infection or Listeriosis, for example (12).
Kefir will also regulate the production of immune proteins, including antibodies, in the gut via the production of different short chain fatty acids (SCFAs), which thus regulates the immune response from the rest of the body (13). It was speculated not too long ago that drinking kefir would help overcoming COVID-19 for two main reasons – 1, the pH of kefir is quite low, and the COVID-19 virus struggles to replicate in such a pH, and 2, by inhibiting the production of inflammatory cytokines (immune proteins) kefir prevents the massive inflammatory response that can make some people so unwell and even die. (The inflammatory response is what causes fever, swelling, and pain when you are unwell, it generally works at helping your body overcome illness but sometimes it can go into overdrive and put more stress on the body).
In conclusion, there is a decent and growing amount of evidence that kefir can alter your microbiome to create one that is considered healthier, it can support your metabolism to aid in ameliorating obesity and diabetes, and it supports a healthy functioning immune system (among other things that we’ll save for another day). It’s also important to remember that kefir is quite a complicated product microbially, and when made with grains the microbial content will evolve over time (a bit like a sourdough mother) and everyone’s kefir grains will be slightly different. A lot of researchers avoid these confounding variables by simply investigating one or other probiotic species, and so studies concerning kefir are still quite limited. Thank you all for reading, hopefully this has got you in the mood to try the Nettlebed Creamery kefir!
1. Kim DH, Chon JW, Kim H, Seo KH. Modulation of intestinal microbiota in mice by kefir administration. Food Sci Biotechnol [Internet]. 2015 Aug 3 [cited 2023 Feb 28];24(4):1397–403. Available from: https://link.springer.com/article/10.1007/s10068-015-0179-8
2. Kim DH, Jeong D, Kang IB, Lim HW, Cho YJ, Seo KH. Modulation of the intestinal microbiota of dogs by kefir as a functional dairy product. J Dairy Sci [Internet]. 2019 May 1 [cited 2023 Feb 28];102(5):3903–11. Available from: https://pubmed.ncbi.nlm.nih.gov/30827566/
3. Bellikci-Koyu E, Sarer-Yurekli BP, Akyon Y, Aydin-Kose F, Karagozlu C, Ozgen AG, et al. Effects of Regular Kefir Consumption on Gut Microbiota in Patients with Metabolic Syndrome: A Parallel-Group, Randomized, Controlled Study. Nutrients [Internet]. 2019 Sep 1 [cited 2023 Feb 28];11(9). Available from: https://pubmed.ncbi.nlm.nih.gov/31487797/
4. Milani C, Duranti S, Bottacini F, Casey E, Turroni F, Mahony J, et al. The First Microbial Colonizers of the Human Gut: Composition, Activities, and Health Implications of the Infant Gut Microbiota. Microbiol Mol Biol Rev [Internet]. 2017 Dec [cited 2023 Mar 1];81(4). Available from: https://pubmed.ncbi.nlm.nih.gov/29118049/
5. Pinart M, Dötsch A, Schlicht K, Laudes M, Bouwman J, Forslund SK, et al. Gut Microbiome Composition in Obese and Non-Obese Persons: A Systematic Review and Meta-Analysis. Nutrients [Internet]. 2021 Jan 1 [cited 2023 Mar 1];14(1). Available from: https://pubmed.ncbi.nlm.nih.gov/35010887/
6. Bourrie BCT, Cotter PD, Willing BP. Traditional kefir reduces weight gain and improves plasma and liver lipid profiles more successfully than a commercial equivalent in a mouse model of obesity. J Funct Foods. 2018 Jul 1;46:29–37.
7. Kim DH, Jeong D, Kang IB, Kim H, Song KY, Seo KH. Dual function of Lactobacillus kefiri DH5 in preventing high-fat-diet-induced obesity: direct reduction of cholesterol and upregulation of PPAR-α in adipose tissue. Mol Nutr Food Res [Internet]. 2017 Nov 1 [cited 2023 Mar 1];61(11). Available from: https://pubmed.ncbi.nlm.nih.gov/28691342/
8. Tiss M, Souiy Z, Abdeljelil N ben, Njima M, Achour L, Hamden K. Fermented soy milk prepared using kefir grains prevents and ameliorates obesity, type 2 diabetes, hyperlipidemia and Liver-Kidney toxicities in HFFD-rats. J Funct Foods. 2020 Apr 1;67:103869.
9. Rosa DD, Grześkowiak LM, Ferreira CLLF, Fonseca ACM, Reis SA, Dias MM, et al. Kefir reduces insulin resistance and inflammatory cytokine expression in an animal model of metabolic syndrome. Food Funct [Internet]. 2016 Aug 1 [cited 2023 Mar 1];7(8):3390–401. Available from: https://pubmed.ncbi.nlm.nih.gov/27384318/
10. Ostadrahimi A, Taghizadeh A, Mobasseri M, Farrin N, Payahoo L, Beyramalipoor Gheshlaghi Z, et al. Effect of Probiotic Fermented Milk (Kefir) on Glycemic Control and Lipid Profile In Type 2 Diabetic Patients: A Randomized Double-Blind Placebo-Controlled Clinical Trial. Iran J Public Health [Internet]. 2015 [cited 2023 Mar 1];44(2):228. Available from: /pmc/articles/PMC4401881/
11. Seo MK, Park EJ, Ko SY, Choi EW, Kim S. Therapeutic effects of kefir grain Lactobacillus-derived extracellular vesicles in mice with 2,4,6-trinitrobenzene sulfonic acid-induced inflammatory bowel disease. J Dairy Sci. 2018 Oct 1;101(10):8662–71.
12. Jeong D, Kim DH, Kang IB, Kim H, Song KY, Kim HS, et al. Characterization and antibacterial activity of a novel exopolysaccharide produced by Lactobacillus kefiranofaciens DN1 isolated from kefir. Food Control. 2017 Aug 1;78:436–42.
13. Corrêa-Oliveira R, Fachi JL, Vieira A, Sato FT, Vinolo MAR. Regulation of immune cell function by short-chain fatty acids. Clin Transl Immunol [Internet]. 2016 Apr 1 [cited 2023 Mar 3];5(4):e73. Available from: https://onlinelibrary.wiley.com/doi/full/10.1038/cti.2016.17