Fermented Foods: Definitions, Microbial Characteristics, and Impact on Gastrointestinal Health
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Adapted with AI for easier reading — original article available below (CC BY)
Citation : Dimidi, E.; Cox, S.R.; Rossi, M.; Whelan, K. Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease. Nutrients 2019, 11, 1806. https://doi.org/10.3390/nu11081806
Copyright : © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Abstract
Fermented foods are made through controlled microbial growth and enzymatic transformation of food components. With rising popularity due to potential health benefits, this review covers common fermented foods—kefir, kombucha, sauerkraut, tempeh, natto, miso, kimchi, sourdough bread—their mechanisms of action for gut health, and supporting clinical evidence. Positive effects may be due to probiotic microorganisms, bioactive peptides, improved conversion of food compounds, and reduced anti-nutrients. While clinical trials are limited, certain foods like kefir, sauerkraut, natto, and sourdough show promise for digestive wellness.
Keywords: kefir; kombucha; sauerkraut; miso; natto; tempeh; soy; kimchi; sourdough; fermented food
Introduction
Fermentation is an ancient technique for food preservation and flavor. Fermented foods can be created by spontaneous (wild) fermentation or with starter cultures (“culture-dependent”), like kefir or natto. Health benefits may result from:
- High doses of probiotic bacteria (LAB)
- Bioactive peptides and polyamines produced during fermentation
- Enhanced conversion of food compounds (flavonoids, phenolics)
- Increased prebiotics and vitamin concentrations
- Reduced anti-nutrients and toxins (e.g., phytic acid in soy)
Most products contain at least 106 microbes per gram. Microorganisms may temporarily colonize the gut, supporting immune and metabolic function and competing with pathogens.
Description and Microbial Content of Common Fermented Foods
| Food | Microbial Content (Main Genera) | Fermentation Type | Notes |
|---|---|---|---|
| Kefir | Lactobacillus, Lactococcus, Leuconostoc, Acetobacter, Yeasts | Starter culture | Fermented milk, grains with symbiotic bacteria & yeast |
| Kombucha | Acetobacter, Gluconobacter, Lactobacillus, Saccharomyces (yeast) | Starter (SCOBY) | Fermented tea, acetic acid, and ethanol production |
| Sauerkraut | Leuconostoc, Lactobacillus, Pediococcus | Spontaneous | Cabbage + salt, lactic acid fermentation |
| Tempeh | Rhizopus oligosporus | Starter culture (mold) | Fermented soybean cake |
| Natto | Bacillus subtilis | Starter culture | Fermented whole soybeans |
| Miso | Aspergillus oryzae | Starter culture | Fermented soybean paste |
| Kimchi | Leuconostoc, Lactobacillus, Weissella, Enterococcus | Spontaneous | Fermented vegetables, usually cabbage |
| Sourdough Bread | Lactobacillus, Leuconostoc, Saccharomyces | Spontaneous & starter | Fermented flour, yeast and bacteria |
Kefir
Kefir is produced by adding “kefir grains”—cultures of bacteria and yeast—to milk. Its main microbes are lactobacilli, lactococci, and several yeast types (Kluyveromyces, Saccharomyces). Benefits described in clinical studies include:
- Better tolerance for lactose than regular milk
- May improve stool frequency for constipation sufferers
- Can increase Lactobacillus and hemoglobin levels (Crohn’s disease)
- Improved Helicobacter pylori eradication rates during antibiotic therapy
Figure: Microbial composition of kefir grains (Lactobacillus, yeasts, etc.)
Kombucha
Kombucha is a fermented tea made with a symbiotic culture of bacteria and yeast (SCOBY). Highlights:
- Microbial composition depends on tea type, starter, and fermentation time
- Produces acetic acid (gives sour taste, acts as antimicrobial)
- Animal studies suggest blood sugar regulation, antioxidant properties
- No human clinical trials to-date
Figure: SCOBY and fermentation process diagram
Sauerkraut
Sauerkraut is cabbage fermented with salt, relying on spontaneous lactic acid bacteria (LAB) fermentation.
- Microbes include Leuconostoc, Lactobacillus, Pediococcus
- Contains conjugated linoleic acid, glucosinolates
- May reduce IBS symptoms (effect seen for pasteurized and unpasteurized forms)
- High consumption in some studies linked to increased cancer risk
Table: Clinical trial outcomes on sauerkraut for GI disorders
Fermented Soy Products: Tempeh, Natto, Miso
- Tempeh: Mold fermentation, rich in protein and vitamins
- Natto: Bacillus fermentation, high in vitamin K2 and nattokinase
- Miso: Fermented by Aspergillus, probiotic-rich seasoning
Some evidence supports digestive health benefits, though clinical studies are limited.
Kimchi
Kimchi is a traditional Korean fermented vegetable dish, using mixed cultures and spontaneous fermentation. Noted for anti-inflammatory, antimicrobial, and antioxidant benefits, mainly attributed to LAB content. Few robust human clinical studies exist.
Sourdough Bread
Sourdough bread combines spontaneous and starter fermentation. Key points:
- Reduces FODMAPs (better tolerated by people with IBS)
- Improves nutrient bioavailability
- Enhances flavor and texture
Conclusions
Fermented foods provide a diverse range of microorganisms and bioactive compounds. While the outlook for gut health is promising, clinical studies are still limited beyond kefir and sauerkraut. Continued research is needed to fully understand digestive health benefits.
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