Chances are, you’ve been sleeping on fermented foods for most of your life. They’re “not a natural part of our diet like in a lot of other populations,” Amy Burkhart, a physician and registered dietitian who specialises in gut health, says. Germany has sauerkraut, Korea has kimchi, China has stinky tofu, Japan has miso, but Americans and Brits don’t have a signature fermented dish.

But interest in fermented food is growing steadily as people become more cognisant of its far-reaching benefits for the gut. And unlike some contemporary nutrition trends (looking at you, protein craze), it’s not all hype: Eating a diet rich in fermented foods really is a big win for your digestion, Alma Simmons, a registered dietitian at the Ohio State University Wexner Medical Center, says.

Below, we’ll break down how exactly fermented foods translate into a digestive boost; which fermented foods are best; whether fermented foods pose any health risks; and what you should keep in mind if you’d like to incorporate them into your diet more often. (Number one: “Don’t be wary of trying them!” Dr. Burkhart says.)

Why are fermented foods so good for gut health?

Fermentation involves the breakdown of carbohydrates like sugars and starches by beneficial microorganisms like bacteria, yeasts and moulds, especially lactic acid-producing bacteria. In nutrition-speak, these microorganisms are often termed “probiotics.” When you ingest these microbes in fermented foods, drinks, or probiotic supplements, they can positively affect your digestive system in a multitude of ways. Not only do they support your gut microbiome – the collection of microorganisms that live in your digestive tract – but they also strengthen the tissue that lines the gut (a.k.a. the “gut barrier”), improve your body’s ability to absorb nutrients, and reduce digestive symptoms like gas, bloating and diarrhoea.

In addition to their GI effects, these microbes can also benefit your health in other ways. They reduce inflammation, mediate your immune response, balance blood sugar and lower harmful LDL cholesterol and triglyceride levels. Plus, “there is some evidence that they can improve mood and cognition,” Dr. Burkhart says. What’s more, she notes, many of these non-digestive perks may boost digestive health indirectly – a “circular effect.” Inflammation, for example, is widely believed to be a factor in autoimmune conditions, including digestive disorders like IBD and celiac disease, so by that token decreasing it could further reduce symptoms.

More recently, research has emerged to suggest that the byproducts of fermentation (like lactic acid from lactic acid bacteria) can enhance digestion in their own right. Known as “metabolites,” they encompass a diverse array of compounds, including acids, peptides, vitamins, and phenols. “We don’t really know all of their effects, but we know they’re beneficial, just like the probiotics,” Dr. Burkhart says. For example, phenols alone are primarily responsible for the increased antioxidant activity noted in fermented foods.

What are the best fermented foods?

While all fermented foods are worthwhile for the reasons outlined above, some “have stronger, better documented effects on gut health than others, depending on their microbial composition and bioactive components,” Simmons says. Both cooking and pasteurization kill beneficial microbes, so many fermented foods are sold raw and unpasteurized. But even those that are cooked and pasteurized still count since they retain the metabolites. Here are a few examples.

• Plain Greek yogurt: Look for yogurt labeled as containing “live and active cultures,” Simmons says. That refers to the lactic acid bacteria Lactobacillus bulgaricus and Streptococcus thermophilus, according to the International Dairy Foods Association, which can help fight pathogenic (harmful) bacteria like E. coli, Clostridium, and salmonella; restore balance in the digestive tract after a course of antibiotics; and even counter lactose intolerance since they help break down the lactose in dairy, Simmons explains. Because of this, “people who are lactose intolerant can often tolerate things like kefir or cheese, which are fermented,” more readily than, say, plain ol’ cow’s milk, Dr. Burkhart notes.
• Kefir: Of all fermented foods, kefir is among the most well-studied. It “contains a mixed symbiotic community of lactic acid bacteria and modulates microbiota composition more broadly than yogurt,” Simmons says. Plus, it’s been shown to decrease inflammation, Dr. Burkhart adds.