Fermented foods have been dietary staples for centuries. Historically, fermentation was a vital food preservation method, helping limited resources last longer and making certain foods more digestible. Fermentation involves bacteria and yeast that naturally outcompete harmful microorganisms, making the food safer to consume and allowing it to be stored for longer periods. This process also produced foods with enhanced flavors and nutritional profiles.
Globally, over 5,000 varieties of fermented foods and beverages are consumed, with evidence suggesting they reduce disease risk and promote health and longevity. Some of the most common types of fermented foods are yogurt, kefir, sauerkraut, kimchi, miso, tempeh, and kombucha.
What Are Fermented Foods?
The International Scientific Association for Probiotics and Prebiotics (ISAPP) defines fermented foods as “foods made through desired microbial growth and enzymatic conversions of food components.” These processes alter the food’s structure, making it more nutritious and easier to digest.
Not all fermented foods retain live microorganisms by the time they are consumed. For example:
Bread: Baking destroys live microbes.
Beer and Wine: Post-production steps, like filtration, remove live cultures.
While the greatest health benefits are likely related to fermented foods that still contain live, active cultures, there can still be benefits in consuming fermented foods in which the cultures have "died" though are still present.
Health Mechanisms of Fermented Foods
Enhanced Nutritional Value
Breaks down "anti-nutrients"
Breaks down lactose
Lowers glycemic index
Improves absorption of nutrients
Enhances benefits of polyphenols
Fermentation breaks down anti-nutrients to increase the nutritive value of foods. Anti-nutrients block the absorption of nutrients, effectively cancelling out the potential benefits. For example, phytic acid is an anti-nutrient founds in certain grains, legumes and root vegetables that blocks the absorption of minerals like zinc, calcium and magnesium.
During the fermentation process, high-calorie monosaccharides, or sugars, are broken down by bacteria. This lowers the glycemic index and results in less spikes in blood sugar. Fermentation also helps digest complex sugars, proteins and fats, easing digestion and improving absorption. Polyphenols, antioxidant compounds that reduce inflammation and support the microbiota, become more bioavailable after fermentation.
Fermented dairy products, like yogurt and kefir, include bacteria that break down lactose, using lactose as their food source. As a result, these is less lactose in the final product, making it easier to digest for all individuals, but especially those with lactose intolerance. While not everyone with lactose intolerance will feel comfortable eating fermented dairy products, some may be able to include this in a balanced diet.
Gut Microbiota Diversification
Survives digestion and reaches colon/microbiota
Transfers beneficial genes to microbiota
Prevents colonization by infectious bacteria
Creates positive byproducts that support the gut and overall health
Many of the bacteria in fermented foods can survive the digestive process and reach the colon, where they interact with the gut microbiota. This interaction can allow for the transfer of beneficial genes, making the microbiota more robust and resilient.
These bacterially typically do not permanently colonize the gut, though the temporary colonization can also provide benefit. While in the gut, they consume resources and compete with potential pathogenic bacteria, making it more difficult for these bacteria to cause an infection. They can also create beneficial byproducts, such as short-chain fatty acids (SCFA), that strengthen the gut wall and improve metabolism.
Immune System Modulation
Strengthens immune system
Reduces allergies and eczema
Approximately 70% of the immune system resides in the gut. The immune system learns from interactions with the gut microbiota and the byproducts they create, beginning in early childhood. This training of the immune system helps keep it strong enough to manage infections, yet prevents over-reaction of the immune system that occurs in autoimmune conditions.
Adding in fermented foods provides additional training of the immune system, and when eaten consistently, can lower the risk of allergies and eczema. As the bacteria in fermented foods often do not stay in the colon for too long, daily intake is needed for the greatest benefit.
The exact mechanism of the immune-modulating effects of fermented foods are not well-defined given lack of research, though there are likely several factors that contribute.
Direct contact between bacteria in fermented foods and the immune system
Production of immune-modulating chemicals by bacteria in fermented foods
Reduction in Leaky Gut
Improves intestinal barrier function
Reduces intestinal permeability
Reduces systemic inflammation
Increased intestinal permeability, or leaky gut, occurs when there is poor integrity of the gut lining and mucosa. This can result from imbalances in the gut microbiome and can lead to inflammation throughout the body.
Bacteria found in fermented foods can help to strengthen the intestinal lining, reducing leaky gut and inflammation. This improvement is likely related to the bacteria from the fermented foods changing the microbiome composition and by creating byproducts that lower inflammation in local area.
Increased Bioactive Compounds
Vitamins B12 and K2
Antimicrobial compounds
SCFA that support gut and metabolism
Blood pressure lowering compounds
During the process of fermentation, several byproducts can be created by the bacteria, including vitamins B12 and K2 and antimicrobial compounds. This not only increases the bioavailability of nutrients in the fermented food, it also protects the food against contamination from harmful bacteria, making it safer to eat. These bacteria can also create active compounds that improve metabolic health, cardiovascular health, and can be healing and repairative to the gut lining.
Conditions Fermented Foods Can Support
Lactose Intolerance
Fermented dairy products naturally contain lower levels of lactose because the bacteria present break it down during fermentation. Kefir, in particular, has a high concentration of beneficial bacteria, making it more tolerable for many individuals. However, not everyone with lactose intolerance can eat fermented dairy comfortably. If you're unsure, start with small amounts and gradually increase your intake to assess tolerance.
Diarrhea Management
In young children, fermented foods have demonstrated benefits in reducing the severity and duration of infectious diarrhea, such as gastroenteritis.
IBS and IBD Support
Fermented foods play a role in managing gut inflammation, improving microbiota balance, and alleviating symptoms like bloating and diarrhea in individuals with IBS or IBD.
Cancer Prevention
Regular consumption of yogurt has been linked to a decreased risk of certain cancers, including bladder, colon, and esophageal cancers.
Mental Health
Research suggests a connection between fermented dairy products, such as yogurt and cheese, and reduced rates of depression. This may be due to the influence of gut bacteria on gut-brain communication.
Inflammation Reduction
Fermented foods can lower markers of systemic inflammation, though the evidence is mixed, as not all inflammatory markers are consistently affected.
Cardiovascular Health
Cultured yogurt and cheese consumption is associated with reduced heart disease risks and improved cholesterol profiles. While cheese can be beneficial, it should be consumed in moderation due to its saturated fat content.
Blood Sugar Control
A meta-analysis of studies found that fermented foods help improve blood sugar control by reducing fasting blood glucose, insulin resistance, and LDL cholesterol.
Cognitive Health
When combined with a Mediterranean diet, fermented foods have been linked to a slower rate of cognitive decline in older adults, suggesting benefits for long-term brain health.
How to Incorporate More Fermented Foods
Yogurt: Add ¼ cup daily to smoothies, granola, or enjoy it plain.
Look for yogurt that is plain, with no added sugar.
If you don't like the tart flavor, add small amounts of honey or maple syrup and decrease the amount of sweetener over time so you can adjust.
Sauerkraut: Use as a topping for eggs, bowls, or sandwiches for a tangy twist.
Making sauerkraut at home is fun and easy!
Kimchi: Incorporate into stir-fries, fried rice, or Asian-inspired dishes. Just remember that cooking kimchi will kill the cultures, so ideally add this last!
Fermented Vegetables: Unlike conventional "pickled" vegetables that are made with vinegar, spontaneous ferments of vegetables will look cloudy and have a lab indicating it's been fermented.
Kombucha: Swap sodas for this probiotic-rich beverage.
Who Should Avoid Fermented Foods?
Histamine Intolerance
Fermented foods are high in histamine, which may trigger symptoms in sensitive individuals.
Candida Overgrowth
Natural ferments typically contain yeast, which may exacerbate overgrowth, though yogurt (with its bacterial dominance) can be beneficial.
Immunocompromised Individuals
Due to the presence of live microorganisms, there’s a slight risk of infection.
Conclusion
Fermented foods are more than just a flavorful addition to your diet—they are a powerful tool for enhancing gut health, reducing inflammation, and supporting the immune system. From ancient preservation methods to modern health food trends, the benefits of fermentation are well-documented and compelling. While more research is needed to fully understand their long-term impact, incorporating fermented foods into your meals is a delicious and beneficial way to support your health.
Start small, experiment with flavors, and enjoy the transformative power of fermented foods!
Not sure if fermented foods are a good fit for you? Always make sure to consult with a health professional if you aren't sure about changes in diet or lifestyle.
Disclaimer
The information provided in this blog and throughout the website is intended for educational purposes only and should not be considered, or used as a substitute for, medical advice. The content is not meant to diagnose, treat, or cure any medical condition. This blog does not constitute the practice of any medical, nursing or other professional health care advice, diagnosis or treatment. Always consult with a qualified healthcare provider before making any changes to your health regimen or starting new treatments, and never disregard professional medical advice or delay seeking care because of something that you have read on this blog, website or in any linked materials. Your individual needs and circumstances should be evaluated by a medical professional to ensure safe and appropriate care. If you are experiencing a medical emergency, please call 911 or call for emergency medical help on the nearest telephone immediately.
References
“Consumption of Fermented Foods Is Associated with Systematic Differences in the Gut Microbiome and Metabolome - PMC.” Accessed December 12, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC7380580/.
“Fermented Dairy Foods Intake and Risk of Cancer - PubMed.” Accessed December 11, 2024. https://pubmed.ncbi.nlm.nih.gov/30374967/.
“Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease - PMC.” Accessed December 11, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC6723656/.
“Fermented Foods, Health and the Gut Microbiome - PMC.” Accessed December 12, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC9003261/.
Luo, Yupeng, Zhuo Li, Liya Gu, and Kui Zhang. “Fermented Dairy Foods Consumption and Depressive Symptoms: A Meta-Analysis of Cohort Studies.” PLOS ONE 18, no. 2 (February 6, 2023): e0281346. https://doi.org/10.1371/journal.pone.0281346.
Olayanju, Adetokunbo, Duane Mellor, Yunus Khatri, and Neil Pickles. “The Efficacy of Fermented Foods in the Treatment and Management of Diarrhoeal Diseases: A Systematic Review and Meta-Analysis.” Nutrition and Health 29, no. 1 (March 2023): 71–83. https://doi.org/10.1177/02601060221095678.
“Potential Neuroprotective Effects of Fermented Foods and Beverages in Old Age: A Systematic Review - PMC.” Accessed December 11, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC10313410/.
“The International Scientific Association for Probiotics and Prebiotics (ISAPP) Consensus Statement on Fermented Foods | Nature Reviews Gastroenterology & Hepatology.” Accessed December 10, 2024. https://www.nature.com/articles/s41575-020-00390-5.
“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 - PMC.” Accessed December 12, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC8001875/.
Zhang, Kui, Xiaogang Chen, Lin Zhang, and Zhenhua Deng. “Fermented Dairy Foods Intake and Risk of Cardiovascular Diseases: A Meta-Analysis of Cohort Studies.” Critical Reviews in Food Science and Nutrition 60, no. 7 (2020): 1189–94. https://doi.org/10.1080/10408398.2018.1564019.
Zhang, Xiao-Feng, Yue Qi, Yong-Ping Zhang, Jin-Lan Deng, Xiao-Li Chen, Ruo-Nan Li, Qi-Lun Zhou, and Jian-Ming Fan. “Fermented Foods and Metabolic Outcomes in Diabetes and Prediabetes: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.” Critical Reviews in Food Science and Nutrition 64, no. 26 (October 13, 2024): 9514–31. https://doi.org/10.1080/10408398.2023.2213770.