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What Fermented Foods Can do for Your Immune System

Our gut is home to thousands of different microbial species including bacteria, fungi, viruses and other microorganisms that are collectively known as the gut microbiome. This internal metropolis of busy microbes housed in our GI tract includes bacterial heroes that help us digest and absorb nutrients, produce hormones and essential amino acids. And then, there are the not so friendly bacteria taking up residence in our gut that can cause inflammation or make us ill. Studies have linked gut bacteria to mood disorders, tendency to obesity, cardiovascular health and more recently, immune system health.

With 70-80% of immune cells being present in the gut[1], there is an intricate interplay between the intestinal microbiota, the intestinal epithelial layer and the local mucosal immune system. This major site of immune activity is influenced by what we choose to eat. What we put in our stomachs plays a significant role in determining what kinds of microbes live in our intestines.

If our diet contains copious amounts of refined sugar, artificial sweeteners or is high in saturated fats, we’re welcoming in chronic inflammation, feeding not so friendly bugs and altering the composition of our microbiome for the worse.  If we’re consuming a high fibre, plant-rich diet with a diverse range of fruits, vegetables, whole grains and legumes, we’re supporting the growth and maintenance of beneficial microbes. If we’re incorporating fermented foods into our diet, we’re introducing beneficial bacteria into our guts to further populate and grow our microbiome diversity.

Low gut diversity has been associated with a number of chronic illnesses including obesity, insulin resistance, allergies, colorectal cancer, Crohn’s disease, ulcerative colitis and more. This is why researchers continue to investigate the relationship between our inner microbial communities and overall health outcomes.

A recent study conducted by the Stanford School of Medicine looked at how fermented foods in particular influence microbiome diversity and how this impacts immune response. Thirty-six healthy adults participated in the clinical trial and were randomly assigned a ten-week diet that included either fermented or high-fibre foods. Researchers found that the fermented food group increased their overall microbial diversity, whereas the microbial communities of the high-fibre group simply remained stable.

Researchers also noted that for the fermented food group, four types of immune cells showed less activation and blood samples revealed decreased levels of 19 inflammatory proteins.  For those in the high fibre diet group, researchers were surprized to see that none of the 19 inflammatory proteins decreased. One protein that was measured was interleukin 6 (IL-6). High IL-6 levels have been associated with rheumatoid arthritis, type 2 diabetes and more recently, with increased risk of mortality and severity of pneumonia in patients diagnosed with Covid 19.[2]

It is known that high-fibre diets are associated with lower rates of mortality, so don’t discount the power of fibre in your diet! But this ability to alter the gut microbiome through fermented food consumption to ultimately combat inflammation and improve immune status shows significant promise.

Fermented foods are foods and beverages produced through controlled microbial growth and the conversion of food components through enzymatic action. Basically, fermented foods contain microorganisms that give our bellies a helpful dose of probiotics.  Lactic acid bacteria have been some of the most studied microorganisms. During fermentation, these bacteria synthesize vitamins and minerals, produce biologically active peptides and remove some non-nutrients. Biologically active peptides are produced by the bacteria responsible for fermentation. Among these peptides, conjugated linoleic acids (CLA) have a blood pressure lowering effect, exopolysaccharides exhibit prebiotic properties, bacteriocins show anti-microbial effects, sphingolipids have anti-carcinogenic and anti-microbial properties, and bioactive peptides exhibit antioxidant, anti-microbial, opioid antagonist, anti-allergenic and blood pressure lowering effects.[3] Other studies have also found probiotics effective at reducing the duration and severity of the common cold in both children and adult populations.[4]

Fermented food examples include:

  • Yogurt
  • Kefir
  • Cottage cheese with live cultures
  • Tempeh
  • Fermented sausage (ex. salami)
  • Miso
  • Kimchi
  • Apple cider vinegar
  • Pickles
  • Sauerkraut
  • Vegetable brine drinks
  • Sour cream
  • Soy sauce
  • Kombucha

Clearly, the probiotics found in fermented foods provide a multitude of benefits in addition to improving immune status. Thus making an effort to incorporate them regularly in the diet can help to fortify our gut health and overall wellness.


[1] Wiertsema SP, van Bergenhenegouwen J, Garssen J, Knippels LMJ. The Interplay between the Gut Microbiome and the Immune System in the Context of Infectious Diseases throughout Life and the Role of Nutrition in Optimizing Treatment Strategies. Nutrients. 2021 Mar 9;13(3):886. doi: 10.3390/nu13030886. PMID: 33803407; PMCID: PMC8001875.

[2] Guirao JJ, Cabrera CM, Jiménez N, Rincón L, Urra JM. High serum IL-6 values increase the risk of mortality and the severity of pneumonia in patients diagnosed with COVID-19. Mol Immunol. 2020;128:64-68. doi:10.1016/j.molimm.2020.10.006

[3] Şanlier N, Gökcen BB, Sezgin AC. Health benefits of fermented foods. Crit Rev Food Sci Nutr. 2019;59(3):506-527. doi: 10.1080/10408398.2017.1383355. Epub 2017 Oct 20. PMID: 28945458.

[4] King S, Glanville J, Sanders ME, Fitzgerald A, Varley D. Effectiveness of probiotics on the duration of illness in healthy children and adults who develop common acute respiratory infectious conditions: a systematic review and meta-analysis. Br J Nutr. 2014 Jul 14;112(1):41-54. doi: 10.1017/S0007114514000075. Epub 2014 Apr 29. PMID: 24780623; PMCID: PMC4054664.

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