Fermentation

Fermentation in Food and Nutrition

Fermentation is a metabolic process in which microorganisms — bacteria, yeasts, or molds — convert carbohydrates (sugars and starches) into acids, gases, or alcohol under anaerobic or low-oxygen conditions. Humans have relied on fermentation for millennia to preserve food, improve flavor, and increase the digestibility and nutritional value of raw ingredients. From a nutritional science perspective, fermentation transforms food matrices in ways that can meaningfully alter their impact on human health.

Common fermented foods include yogurt, kefir, cheese, sauerkraut, kimchi, sourdough bread, miso, tempeh, natto, kombucha, beer, wine, and vinegar. The microbial species responsible for fermentation vary by product: lactic acid bacteria (LAB) dominate dairy and vegetable ferments, while Saccharomyces cerevisiae is central to bread and alcohol fermentation.

Nutritional Changes Induced by Fermentation

Fermentation can alter the nutritional profile of foods in several important ways:

• Reduced antinutrients: Phytates and oxalates, which bind minerals, are partially degraded during fermentation, improving bioavailability of iron, zinc, calcium, and magnesium — particularly important in legume and grain fermentation.
• Increased bioavailability: Protein digestibility improves in fermented legumes such as tempeh due to proteolytic enzyme activity.
• Vitamin synthesis: Certain LAB strains synthesize B vitamins including riboflavin (B2), folate (B9), and cobalamin (B12) analogues.
• Reduced lactose: The lactase activity of fermenting bacteria breaks down lactose in dairy, making products such as yogurt better tolerated by people with lactose intolerance.

Fermentation and Gut Health

A landmark 2021 randomized controlled trial published in Cell demonstrated that a high-fermented-food diet significantly increased microbiome diversity and reduced systemic inflammatory markers compared to a high-fiber diet over 10 weeks. Fermented foods deliver live microorganisms to the gut, though not all survive transit to the colon in high numbers. Even heat-killed organisms and the metabolic byproducts of fermentation (organic acids, bioactive peptides, and postbiotics) may exert independent health effects on the intestinal environment.