Why are bacteria-bearing foods so good for us?
Kristina Campbell, MSc
By now, you've probably heard the news that fermented foods are great for us, and we should all be eating more of them. But why, exactly?
Shredded cabbage, water, salt. That’s it. You throw them together in a glass jar, and then you add the final ingredient: time. Once the mixture has settled for a while, you might see tiny bubbles beginning to form along the sides of the jar if you look closely enough. If you had a microscope, you’d even see the friendly bacteria latching onto the plant material. If you studied the jar for long enough, you’d see that waves of different bacteria proliferate in the jar over time, releasing byproducts that change the acidity and enzymes inside. And you’d end up with a mixture of your shredded cabbage with lactic acid, some acetic and propionic acid, a cocktail of gases (mainly carbon dioxide), a trace amount of alcohol and aromatic esters. In other words, a fantastic batch of fermented sauerkraut.
Fermentation is the process by which carbohydrates, like those in plant material, are converted to acids, gases and/or alcohol. In the case of sauerkraut, the micro-organisms responsible for kicking off the process are lactic acid bacteria (LAB)—a diverse group of bacterial species (mainly Lactobacillus, Leuconostoc and Pediococcus) found naturally on the surface of plants, which produce lactic acid as their main metabolic end product.
Yogurt and some other fermented foods on store shelves are produced in highly controlled environments, so scientists know exactly which strains of bacteria they proffer. But in home fermentation, friendly microbes from the vegetables, the air and the hands of the maker all combine to produce a microbially different batch every time. Although most fermented foods contain strains of bacteria that are potentially beneficial, these live cultures do not fit the accepted definition of a probiotic, since they are simply a random, unnamed mix.
Fermentation is considered very safe, since LAB naturally produce substances that inhibit the growth of food-spoiling bacteria. If you try fermenting at home, however, it’s smart to learn how to tell the difference between benign kahm yeast (a harmless fermentation byproduct) and potentially harmful mold.
Healthy fermented foods have been eaten for millennia. In the beginning, fermentation was a way to preserve. Human groups throughout history then discovered that certain ways of storing food came with an added bonus: changing the food’s flavor and texture.
Only later with advances in microbiology did we come to understand how the bacteria were doing their work in favorite fermented foods like kimchi.
Since the mix of bacteria in each batch is individual and complex, fermented foods are a difficult subject of controlled laboratory study. What scientists know for sure, however, is that the live cultures in fermented foods are key to their health benefits.
Certain bacterial strains, which are present to a greater or lesser extent in a serving of fermented food, have distinct health benefits when tested in isolation. In healthy adults, these bacteria can help prevent acute upper respiratory tract infections, as well as urinary tract infections and allergies, and they can lower cardiovascular disease risk.
Yet a fermented food is more than just the sum of its micro-organisms. Some evidence suggests the food matrix may help boost the beneficial health effects. And when it comes to fermented veggies, the fiber they contain could act as a prebiotic and magnify the effects of the good bacteria, helping them proliferate and produce health-boosting short-chain fatty acids.
Studies have even linked fermented food consumption to mental well-being, with outcomes including lower social anxiety and decreased reactions to negative events, though more comprehensive studies are needed to verify these effects in humans.
Fermented foods aren’t the only way we can ingest beneficial bacteria. In fact, some research shows that you’d need to eat a whole lot of fermented foods in order to get the dose of bacteria shown to produce health benefits in clinical trials.
Probiotic supplements offer an easy way to consume well-researched, precise bacteria strains in large quantities. For example, the probiotic Lactobacillus rhamnosus GG, which is commonly found in supplement form, can help with intestinal issues and stimulate immune responses in many people.
Fermented supplements, like fermented vegan proteins and fermented mushrooms, are a bit different. When it comes to making fermented supplements, bacteria can degrade substances like oxalate, phytate and tannins, making some of the nutrients more available. These supplements don’t contain live micro-organisms when you take them.
Not all fermented foods contain live organisms when you consume them. In some cases (as in transforming cocoa beans into chocolate), live bacteria are eliminated by the time the food is eaten. In other cases (as in kombucha), the bacteria are alive at the time of consumption. The term “fermented foods” generally refers to those that contain live micro-organisms upon ingestion.
True fermented foods are not shelf-stable, so when you’re buying them from a grocery or health food store, look for them in the refrigerator section. Live cultures should be listed on the label, and the food should have an expiration date clearly marked.
Fermented foods have a long history of use, and they offer so many benefits—for both your health and your taste buds. They represent not just the preservation of a food, but also a moment in time: a microbial snapshot. So what are you waiting for? Dig into that delicious kraut.