Fermented Foods: A Simple Way to Support  Your Gut and Your Overall Health 

By: Harlee Palmer

Edited by: Thrive Carolinas

You may have heard that fermented foods are good for your gut.

But what does that actually mean, and why should you care about the bacteria in your digestive tract? 

The answer starts with your gut microbiome: the trillions of bacteria and other microorganisms that live primarily in your digestive tract. These microbes do much more than help you digest food. They interact with your immune system, influence metabolism, help produce important compounds, and communicate with other parts of your body—including the brain. 

One of the simplest ways to support this community is to regularly include fermented foods in your diet. 

What exactly is a fermented food? 

Fermentation is an ancient process in which microorganisms such as bacteria and yeast transform food. 

Think about what happens when: 

• Milk becomes yogurt or kefir 
• Cabbage becomes sauerkraut or kimchi 
• Soybeans become miso or tempeh 
• Flour and water become sourdough 

During fermentation, microbes change the food’s flavor, texture, and nutritional properties. They can also produce compounds such as organic acids and, depending on the food and how it is prepared, make certain nutrients easier to digest or absorb. 

Why are fermented foods good for gut health? 

A healthy ecosystem contains many different microorganisms that interact with one another and with the foods you eat. Research suggests that diet can influence the diversity, composition, and activity of this microbial community. 

Fermented foods are particularly interesting because they can provide both live microorganisms and fermentation-produced compounds that can interact with the gut and the microbes already living there. One of the most important human studies on fermented foods was a randomized controlled trial conducted at Stanford University and published in Cell.

In the 17-week study, healthy adults were assigned to either a high-fiber diet or a diet high in fermented foods. The fermented-food group gradually increased its consumption of foods such as yogurt, kefir, kimchi, kombucha, and other fermented products. Results showed that the high fermented-food diet increased gut microbiome diversity over time and decreased several markers of inflammation. 

Additionally, growing evidence links fermented dairy foods, particularly yogurt and kefir, to changes in the gut microbiome. 

A recent review of studies involving fermented dairy products found that: 

• Six studies reported increases in gut microbial diversity 
• Nine studies reported increases in the relative abundance of Lactobacillus and/or  Bifidobacterium 
• Several studies reported increases in beneficial short-chain fatty acids
• Many studies reported improvements in gastrointestinal symptoms such as abdominal  discomfort and bowel regularity 

Which fermented foods should you eat? 

There is no single “best” fermented food. 

In fact, variety may be more important than choosing one perfect food. Yogurt 

Choose plain yogurt with live and active cultures. Greek yogurt is also a convenient source of protein. 

Kefir 

Kefir is a fermented milk drink containing a diverse community of bacteria and yeasts. It is typically lower in lactose than milk and provides protein and calcium. 

Sauerkraut 

Look for refrigerated sauerkraut that has been fermented rather than simply vinegar-pickled. If you want live microorganisms, choose a product that has not been pasteurized after fermentation. 

Kimchi 

Kimchi combines fermentation with a variety of vegetables and plant compounds. It’s an easy way to add both fermented food and vegetable variety to a meal. 

Miso

Miso is a fermented soybean paste used in soups, dressings, sauces, and marinades. Tempeh 

Tempeh is made from fermented soybeans and provides plant protein, along with the nutritional benefits of soy. 

Kombucha 

Kombucha is fermented tea. If you drink it, check the nutrition label for added sugar. Sourdough 

Sourdough bread undergoes fermentation, but baking generally eliminates most live microorganisms. Fermentation can still change the bread’s characteristics and digestibility. 

Start small and build gradually. 

For example: 

Start with one serving a day 

• ½–1 cup yogurt 
• ½–1 cup kefir 
• 1–2 tablespoons sauerkraut or kimchi 
• A serving of tempeh 
• A small amount of miso in soup or dressing 

If you tolerate fermented foods well, try incorporating different types throughout the week. Eating fermented foods alone is not the goal. 

Your existing gut microbes need food, too. 

That food comes largely from the fiber and plant compounds found in: 

• Vegetables 
• Fruits 
• Beans and lentils 
• Whole grains 
• Nuts and seeds 
• Mushrooms 
• Onions and garlic 
• Asparagus 
• Oats

Many of these foods contain prebiotic fibers and other compounds that gut bacteria can metabolize. 

This creates an important distinction: 

Fermented foods provide microorganisms and fermentation-derived compounds. Fiber-rich plant foods provide fuel for the microbes already living in your gut. A healthy gut diet includes both. 

A few cautions 

• Fermented foods are a healthy addition to your diet, not a treatment or cure for any specific disease. High-quality clinical trials are still limited, so they should not replace medications or medical advice. 
• Some are high in salt (kimchi, sauerkraut, miso, natto) — important if you have high blood pressure, heart failure, or kidney problems. 
• Kombucha and other fermented products may contain small amounts of alcohol and sugar.
• If you have a weakened immune system, are pregnant, or have a serious illness, talk with your healthcare provider before adding unpasteurized fermented foods. 
• Fermented foods are not a substitute for a balanced diet rich in fruits, vegetables, whole grains, and fiber.