Fermented foods offer a trifecta of health benefits: nourishing the microbiome with inflammation-fighting microbes, aiding in digestion, and playing a key role in vitamin production.
“It’s fascinating to recognize that fermented foods have been used for centuries across nearly every culture in the world as a way of preserving foods,” said AMA member Stephen Devries, MD, a preventive cardiologist and executive director of the nonprofit Gaples Institute in Chicago. “And modern nutrition science has shown that fermentation is beneficial not just for food preservation, but also for health.”
However, there’s an important nuance when it comes to finding fermented foods in the supermarket, said Dr. Devries, who joined Jeanette Brooks, host of the Gaples Institute podcast “Medicine with a Fork,” to discuss the benefits of fermented foods for patients.
In order for a food to deliver the health benefits of fermentation, it must contain both live and active cultures. Contrary to popular belief, shelf-stable foods that you find in the nonrefrigerated part of the supermarket—such as unrefrigerated pickles and sauerkraut—do not contain live and active cultures. Dr. Devries advised consumers to read labels carefully to make sure they’re getting products that deliver the intended benefits of fermented foods.
The science behind fermentation
Fermentation occurs when bacteria convert the natural sugars in food into acidic compounds such as lactic acid. Lactic acid accelerates the growth of beneficial bacteria and inhibits the harmful strains responsible for food spoilage.
The process of fermenting vegetables such as pickles, sauerkraut and kimchi involves soaking the food in a salty brine that encourages the growth of naturally occurring bacteria in the vegetables. These bacteria metabolize the sugars in the vegetables into lactic acid, producing the tangy flavor common to fermented foods. The salty brine also keeps harmful bacteria at bay.
The fermentation of dairy products is slightly different. For yogurt, bacteria—often lactobacilli—is added to milk to initiate fermentation. For kefir, the process involves adding a combination of bacteria and yeast.
Other examples of fermented foods include kombucha, a fermented tea, as well as soy products such as miso and tempeh.
Pickling differs from fermentation
It’s important to distinguish between pickling and fermentation, noted Dr. Devries.
Pickling preserves food by creating an acidic environment, often by adding an acid such as vinegar. “The acidity in vinegar preserves the food, but vinegar doesn't support the growth of the beneficial bacteria needed for fermentation,” he explained. For this reason, vegetables preserved in vinegar don't have live bacterial cultures, so they don’t have the same health benefits associated with fermented foods.
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Fermentation reduces inflammation
There's growing evidence that a healthy gut microbiome—the ecosystem of microorganisms in our digestive tract—is closely linked to overall health.
“The most obvious connection between fermented foods and health is that these favorable bacteria in fermented foods contribute to the diverse ecosystem in our microbiome. But there's a lot more to say about the benefits of fermented food other than the addition of the healthy bacteria,” said Dr. Devries.
A landmark study published in the journal Cell found an association between individuals who regularly consumed fermented foods and a reduction in inflammatory markers. Another benefit of fermented foods is that they aid digestion, making them a valuable addition to many diets. People with lactose intolerance often notice that they can consume fermented dairy foods, as the bacteria involved in fermentation partially break down the lactose.
Fermented foods also play an important role in vitamin production. “The byproducts of bacteria in fermented foods include vitamin K and specifically vitamin K2, which is an important regulator of calcium metabolism,” said Dr. Devries. Furthermore, preliminary evidence suggests that fermented foods may boost cognitive function, possibly by suppressing neural inflammation.
How to identify fermented products
“It’s important to know where you won't find fermented products with active cultures,” said Dr. Devries. Those rows of pickles and sauerkraut stored at room temperature on grocery shelves, for example, don’t qualify. The only place in the supermarket where you'll find fermented foods is in the refrigerated section. Refrigeration slows microbial activity sufficiently to protect the desirable bacteria while preventing unwanted overgrowth.
But here’s the tricky part: not all refrigerated products are fermented. Doctors should tell their patients to check the labels of foods such as pickles and sauerkraut or kimchi to see if they explicitly list active bacteria or include the phrase “live and active cultures.”
“That's really the biggest key because some products are initially fermented but then pasteurized afterwards, and although pasteurization extends the food storage life, unfortunately it also destroys the active cultures in the process,” said Dr. Devries.
Yogurt and drinkable kefir are some of the richest sources of live and active cultures, he continued. To be certain, check the label for a list of the active bacteria, or the phrase “contains live and active cultures.”
Check for salt and sugar
Purchasers of fermented products should also check for salt and sugar levels, Dr. Devries cautioned.
Some fermented foods such as pickles, kimchi, and miso have high sodium levels, while some brands of yogurt, kefir, and kombucha can have a surprising amount of sugar.
“The manufacturer may try to offset a bit of the tartness by adding a lot of sugar. So, the healthiest choices of yogurt and kefir are unsweetened and best flavored to taste with fruit or a small amount of honey,” said Dr. Devries.
