Which Fermented Foods Are Really Healthy?

Fermented foods are often one of the best foods for gut health as they contain probiotic bacteria that are thought to have a beneficial effect on the microbes in our gut. But what counts as fermented food, and how do you know you’re eating the right food? Let’s dig.

What are fermented foods?

By definition, “fermented foods” are foods in which microorganisms, including bacteria and yeast, are grown in a food product. These microorganisms partially consume food, and their metabolic products, in turn, change the chemical composition of food.

It is because of this chemical change that fermented foods were invented. If milk is allowed to ferment, it will turn sour, giving it a sour taste. More importantly, it makes the resulting milk, which you might call yogurt, too acidic to allow most bad bacteria to grow in it. Fermenting food is like planting a lawn: just like grass can take over and make it harder for weeds to take root, fermenting food makes it harder for other microbes in food to grow and spoil.

Fermentation is a way of preserving food, but it is also used to change the taste and texture of food, and to make it easier or more enjoyable to eat. For example, if you are lactose intolerant, you may find it easier to eat a piece of cheese than a glass of milk.

What foods are considered fermented? If we define them as foods in which microbes are deliberately allowed to breed, we get a huge list of things from all over the world. Dairy products like yogurt, cheese and kefir also count, as do fermented vegetables like kimchi, sauerkraut and any pickled foods. The list includes kombucha, miso, tempeh, and even sourdough bread. Beer and wine? Also fermented.

But are all these fermented foods the same in terms of health? Not really. Some of these products, if you buy them at the grocery store, are not necessarily fermented the old fashioned way. Others use fermentation as a step in their production but don’t contain any of these beneficial microbes by the time they reach you. And, as you might have guessed from the variety on this list, they are just completely different foods that probably affect our body in different ways.

Why fermented foods are (probably) good for you

To be honest, scientists are still working on why and even if fermented foods are good for us. But so far, everyone agrees that they should probably be considered part of a healthy and varied diet. Beyond that vague statement, things get more complicated.

Many fermented foods contain lactic acid bacteria. These little guys produce lactic acid – the name literally means “lactic acid” – when they are allowed to snack on our food. They are found in yogurt, kimchi, and many traditional pickles. Lactic acid bacteria are considered probiotics: they have a beneficial effect on our health.

While probiotics are often referred to as “good bacteria” that take up residence in the gut, the truth is that probiotics usually don’t take root or settle down. We already have bacteria in our gut, and they’re not going to give up their sweet jobs just because some new guy shows up. But whatever the reason, consuming probiotics has health benefits that have been linked to improved digestion, cardiovascular health, and immunity, just to name a few.

There are also studies suggesting mental health benefits from probiotics and “prebiotics”. Prebiotics are types of fiber that our human enzymes cannot easily digest, but that the bacteria in our gut can digest. Vegetables and grains are good sources of prebiotics, so foods that contain lactic acid bacteria and prebiotic fibers, such as kimchi, contain both.

Why fermented foods may not always be healthy

Despite all the hype, we don’t have much hard evidence to support the benefits of probiotics or fermented foods in general. This 2019 review even concludes that “there is very limited clinical data on the effectiveness of most fermented foods for gastrointestinal health and disease.”

Probiotics and prebiotics in fermented foods may also cause or exacerbate certain health problems . Bloating is one of the common side effects, simply because there is a lot going on in our intestines when we eat them. Not every personal ecosystem is comfortable with accepting newcomers.

Fermented foods also contain a cocktail of various natural chemicals that can be good (and sometimes bad) for us. Histamine, for example, is a compound that you may know from its role in allergies. But histamine can also occur in fermented foods, causing allergy symptoms in people who are especially sensitive to histamine.

There are also food safety concerns, especially with home fermented products. Traditional ways of fermenting foods usually work pretty well, but it’s really helpful to have experience with the specific fermented foods you’re trying to cook so you can recognize when the wrong microbes are growing. If you’ve ever gotten so into making kombucha that you’ve been poring over photos on blogs trying to determine if your SCOBY is doing something normal-weird or terribly-weird , you know what I mean.

Which grocery store foods are actually fermented?

So, you would like to add more fermented foods to your diet. Chill! But just knowing that certain foods can be fermented doesn’t mean the ones you’ve bought from the store are actually fermented .

Take cucumbers. The traditional way to prepare any pickled vegetable is to soak it in brine. The salt in the brine is hostile to many of the microbes that would otherwise like to grow on your vegetables, while leaving room for the lactic acid bacteria we know and love. When they emerge and begin to multiply, these little guys eat the carbohydrates in the vegetables and produce acid. Leave your pickles to marinate long enough and you’ll get that sour-salty fermented flavor we all know and maybe love.

But if you’ve ever cooked quick cucumbers, you didn’t do it this way. You have vegetables and you poured vinegar on them. Boom, you have something that looks like pickle and tastes like pickled cucumber, just made in a different way. (Vinegar is also traditionally a product of fermentation, in which one set of microbes turns sugar into alcohol and a second set turns alcohol into acid.) Some fermentation may have occurred somewhere along the way, depending on which vinegar was used, but you don’t get a mouthful of probiotics when you eat quick pickles.

If you want an old-fashioned version, look for “lacto-fermented” pickles from a specialist supplier. (Most pickles in grocery stores are vinegar.) Fermented vegetables with live cultures, including pickles and kimchi, will be refrigerated to slow down microbial growth. If you leave them at room temperature or even in the refrigerator for an unusually long time, they can build up pressure and even, in extreme cases, explode.

If you buy yogurt, the FDA requires the yogurt manufacturer to tell you if the yogurt contains live microbes. (The phrase “contains live and active cultures” is optional if they are present.)

Sourdough bread uses fermenting microbes as the starter, but by the time the bread is baked, all of these microbes are dead. You’ll still get some fermentation products – hence the flavor – but if you’re looking for live microbes, they’re gone.

You can eat fermented foods in which the microbes have been killed, or foods that were traditionally fermented but are produced differently today. They are not bad for you or anything like that. They often contain the same ingredients, such as prebiotics and bacterial metabolites, that make fermented foods beneficial to health. But if you want to be sure you’re getting products that are actually fermented, check the labels and do your research.