Fermented Foods

Fermented foods, such as yogurt, kefir, pickles, sourdough bread, kimchi and kombucha, are made when bacteria or yeasts convert the sugars and starches in food into lactic acid, alcohol or acetic acid. As part of a balanced diet they can support digestion and the gut flora, but they are not a treatment and do not offer everyone the same benefits.

Fermentation has become popular again in recent years, largely because of growing interest in gut health. The benefits of fermented foods have been known for generations, and today scientific research is looking more closely at how they affect the gut flora. In this article we explain what fermented foods are, what they can realistically do and who should be careful with them.

What is fermentation and how are fermented foods made?

Fermentation is the process by which bacteria and yeasts break down the carbohydrates in food in an environment with little or no oxygen. It produces lactic acid, alcohol or acetic acid; the food becomes tangier, its texture changes and it keeps for longer. In sauerkraut, for example, bacteria naturally present on the cabbage leaves produce lactic acid in a salty, airless environment, and this acid preserves the cabbage.

Fermentation is one of the most economical ways of producing and preserving food and has been used for centuries. Fermented foods and drinks are a staple of almost every cuisine and carry the cultural history of the communities that make them: kimchi in Korea, sauerkraut in Germany and Eastern Europe, miso in Japan and, in Turkey, yogurt, kefir, pickles, tarhana and boza are among the best-known examples.

Which foods are fermented?

There are far more fermented foods in our kitchens than we might think. The best known include:

• Yogurt: Made by the bacterial fermentation of milk. Because some of the lactose in milk is converted into lactic acid, many people with lactose intolerance tolerate yogurt better than milk.
• Kefir: A slightly sour, refreshing drink made by adding kefir grains to milk. Lactic acid fermentation and a small amount of alcoholic fermentation take place together, and it contains a wider range of microorganisms than yogurt.
• Pickles and sauerkraut: Made by fermenting vegetables in brine or in their own juices. Pickles made with vinegar, however, are not fermented.
• Kimchi: A traditional Korean pickle with hundreds of varieties. Vegetables, mainly napa cabbage and radish, are fermented with garlic, ginger and chili flakes.
• Kombucha: A lightly fizzy, tangy drink made by fermenting sweetened tea with a community of bacteria and yeasts known as a “scoby”.
• Miso and tempeh: Miso is a Japanese paste made by fermenting soybeans with rice or barley; tempeh is an Indonesian food in which cooked soybeans are fermented into blocks.
• Boza: A thick, tangy traditional drink made from grains such as millet, wheat or corn; a very small amount of alcohol may form during fermentation.
• Tarhana: Made by kneading flour, yogurt, vegetables and spices and leaving the mixture to ferment for a few days; it is usually eaten as a soup.
• Sourdough bread, aged cheeses and şalgam (fermented turnip juice): Other fermented foods that often appear on our tables.

What are the benefits of fermented foods?

The best-known contribution of fermented foods is that they may support the diversity of the gut flora. Products containing live cultures, such as yogurt and kefir, interact with the beneficial bacteria in the gut. Findings on the positive effects of regular consumption on the gut microbiota are promising, but research is still ongoing.

• Digestion: Fermentation can make some foods easier to digest; yogurt and kefir, for example, contain less lactose than milk.
• Nutritional value: Levels of some B vitamins can increase during fermentation, and some minerals may become easier for the body to use.
• Immunity: A large share of the body’s immune cells is found in the gut, and a healthy gut flora may help the immune system work in balance.
• The gut–brain connection: Because of the close communication between the gut and the brain, the gut is sometimes called the “second brain”. The findings in this area are intriguing but not yet conclusive.

Remember that fermented foods are not medicine. Their effects vary from person to person, and they work best as part of a varied, fiber-rich healthy eating pattern. Gut bacteria feed mainly on the fiber in vegetables, fruit, legumes and whole grains.

Are all fermented foods probiotic?

No; not every fermented food contains live microorganisms. In some products they are inactivated by later processing:

• In sourdough bread, the microorganisms die during baking.
• Pasteurized, heat-treated or canned pickles do not contain live cultures.
• Pickles made with vinegar are not fermented at all.

The term “probiotic” refers to specific live microorganisms that have been shown to benefit health when taken in adequate amounts. If you are looking for live cultures, choose yogurt and kefir labeled “live and active cultures”, or unpasteurized pickles kept in the fridge.

How should you eat fermented foods?

The best approach is to make fermented foods a natural part of your daily diet, in small amounts and with plenty of variety. If you don’t usually eat them, start with small portions; some people notice mild gas and bloating in the first few days.

• A bowl of yogurt or a glass of kefir at breakfast or as a snack
• A few slices of pickles or a spoonful of sauerkraut alongside meals
• Plain products without added sugar
• Label checks: pickles can be salty, and some kombuchas and bozas can be high in sugar

If you ferment at home, use clean containers and don’t eat anything that is moldy, smells bad or has a bulging lid. Homemade kombucha is vulnerable to unwanted microorganisms if hygiene rules are not followed.

Who should be careful, and when should you see a doctor?

Fermented foods are safe for most people, but some situations call for caution or medical advice:

• High blood pressure, heart or kidney disease: Pickles, kimchi, miso and şalgam can be high in salt.
• People with weakened immunity and pregnant women: Unpasteurized products and homemade kombucha may not be recommended because of the risk of infection; ask your doctor.
• People taking certain medicines: Anyone taking an MAO inhibitor should follow their doctor’s advice on tyramine-rich foods such as aged cheese, soy sauce, miso and sauerkraut.
• Histamine intolerance: Fermented and aged foods can cause headaches, flushing or digestive complaints in some people; those with diet-triggered migraine should also keep an eye on their own triggers.
• Diabetes: Sweetened kombucha and boza can raise blood sugar.
• Anyone who needs to avoid alcohol: Bear in mind that kombucha, kefir and boza can contain small amounts of alcohol.

If you have persistent bloating, diarrhea, constipation, abdominal pain or weight loss, see a doctor rather than trying to fix it with fermented foods; these symptoms can be a sign of irritable bowel syndrome or another digestive problem. People with celiac disease should remember that sourdough bread and tarhana contain gluten; for more detail, see our article on gluten-free eating.

At our clinic in Etiler, our dietitian Berna Melis Hepgüler can review your digestive complaints and eating habits and help you add fermented foods to your nutrition plan in a way that suits you.

Frequently asked questions

Can I eat fermented foods every day?

Most healthy people can eat fermented foods such as yogurt, kefir or pickles every day in reasonable amounts. Variety and moderation are what matter; salty pickles and sugary drinks should be kept in check. If you have a chronic condition, agree on the right amount with your doctor or dietitian.

Are fermented foods the same as probiotic supplements?

No. Fermented foods are foods that contain a range of microorganisms and nutrients, whereas probiotic supplements contain specific strains in specific amounts. It is best to decide with your doctor whether you need a supplement.

Is kombucha healthy?

Plain, low-sugar kombucha can be part of a balanced diet, but human studies on its benefits are limited. Some products are quite high in sugar and may contain a small amount of alcohol. Homemade kombucha is not recommended for pregnant women, people with weakened immunity or children.

Homemade or shop-bought pickles?

Pickles made in brine and stored unpasteurized can contain live cultures; vinegar-based or pasteurized pickles do not. With homemade pickles, pay attention to hygiene and salt content, and never eat anything that is moldy or smells bad.

Do fermented foods help you lose weight?

There is no strong evidence that fermented foods cause weight loss on their own. Protein-containing options such as yogurt and kefir can help you feel full, but what really determines weight management is your overall diet, portion control and physical activity.

This content is for information only and does not replace a medical examination. For a nutrition plan that supports your gut health, please get in touch with us.