For thousands of years, people all over the world have been fermenting foods as a method of preservation—meanwhile discovering that the process also imparts interesting flavors and textures. The Chinese workers who built the Great Wall some 5,000 years ago ate fermented vegetables, while ancient Romans and Greeks fermented fish viscera to make the condiment garum (the Worcestershire sauce of the day).
Putting friendly microbes to work
The term fermentation generally refers to a chemical process in which sugars in food are converted into carbon dioxide and acids or alcohols by bacteria, yeast, or molds. It occurs naturally in many foods and is also done intentionally by adding “starter cultures,” commonly bacteria that produce lactic acid (often referred to as “lactic acid bacteria”).
For example, lactic acid bacteria are used to make yogurt, many cheeses (such as Camembert, feta, and goat), buttermilk, and cultured butter, while yeast is added to grains to make beer and to grape juice to make wine. Other traditionally fermented foods include kimchi (a Korean side dish or condiment typically made from fermented cabbage); miso, tempeh, natto, tamari, and soy sauce (from fermented soybeans); kombucha (from fermented black tea); and kefir (a yogurt-like drink). Did you know that traditional pickles, sauerkraut, olives, salami, and crème fraîche are also all fermented foods? Tangy sourdough bread is fermented by both yeast and lactic acid bacteria.
By one estimate, fermented foods make up about one-third of the human diet worldwide, the types consumed depending on the raw ingredients available in the region, as well as local traditions and tastes. Travel to Southeast Asia, for example, and you’re likely to encounter “stinky tofu” and dishes seasoned with “fish paste” or “fish sauce,” from fermented raw or dried fish. In Southern India, you’ll find idli (fermented black lentil paste, made into little cakes) and dosa (fermented rice and lentil batter, fried and eaten like a crepe). In Africa, people make a sour fermented cornmeal beverage called mahewu. Local plants are also fermented for use in traditional medicine—consumed as beverages or applied topically to treat headaches, kidney problems, stomach illnesses, toothaches, infections, and other ailments.
Benefits of fermented foods
Fermentation increases levels and bioavailability of some nutrients (such as zinc, magnesium, and B vitamins), while it reduces “anti-nutrients” (such as phytates, which interfere with absorption of minerals) and other unwanted compounds (such as natural toxins in foods). It reduces lactose in dairy products, making them easier for some people to tolerate.
Some fermented foods also introduce microorganisms into the gut, which may help maintain a healthy digestive system; in turn, byproducts created by them, including bioactive peptides, may have a beneficial effect on blood pressure, cholesterol, immunity, and cancer prevention. Researchers have noted that these bioactive compounds may even have beneficial effects on the brain.
A trio of Korean studies published over the last few years reported various effects from kimchi that may reduce the risk of cardiovascular disease and diabetes. In one, in the Journal of Medicinal Food, participants who consumed this fermented cabbage dish for a week had reductions in blood sugar and cholesterol, with greater improvements seen with higher amounts of kimchi (7 ounces versus ½ ounce a day) and in people with high cholesterol levels at the start. The two other small studies similarly found improvements in blood sugar control and reductions in blood pressure in people who were overweight or obese or had prediabetes. Less benefit was seen with fresh, unfermented cabbage.
More recently, fermented foods were found to be associated with a lower risk of eczema (atopic dermatitis). In an analysis of 10,000 Korean adults, those who consumed fermented foods, including kimchi and beer, most frequently (more than 92 times a month) were 44 percent less likely to have this skin condition than those consuming them least often (in contrast, meat and processed foods were linked to a higher risk). The study was published in the journal Nutrition Research.
On the other hand, as researchers point out, some byproducts of fermentation (notably N-nitroso compounds in pickled vegetables and pickled fish) may have adverse health effects. And observational studies have linked diets high in pickled foods to an increased risk of gastric, esophageal, and nasopharyngeal cancers, possibly due to such byproducts as well as their high sodium content.
When "fermented" foods really aren't
Be aware that some foods we may think of as “fermented” are not always produced this way. For example, canned black olives and most commercial pickles are heat treated or processed in other ways that do not involve fermentation. To ensure that what you buy is actually prepared by fermentation, buy from companies that produce olives, pickles, and other foods in small batches using actual “lacto-fermentation” methods (the information may be on their websites, if not on their labels). Or consider making your own; a good resource is the webpage Canning Pickles & Fermented Foods from the Institute of Agriculture and Natural Resources at the University of Nebraska-Lincoln. If you like yogurt and other fermented dairy products, look for the “live and active cultures” seal from the National Yogurt Association.
Bottom line: Fermented foods, which tend to be more easily digested and more nutritious than their unfermented counterparts, can be part of a healthy diet, though they alone won’t prevent or cure disease, as some proponents claim. Moreover, because they constitute such a wide range of foods, their health benefits cannot be generalized—some (such as yogurt and other fermented dairy products) are likely overall better than others (like salami). Many (including natto, miso, and pickles) are very high in sodium, which may negate some of the possible health benefits, while pickled vegetables may have both benefits and risks. Look for lower-sodium versions if available, and keep moderation in mind, particularly when eating pickled foods.