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.)
The benefits of the nutrient are major, but overdoing it can come with some consequences.
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.
Not feeling Greek yogurt or kefir? No problem. If fermented dairy isn’t your speed, fermented plant products are also effective – mainly due to the activity of specific metabolites.
- Kimchi: This traditional Korean side “is high in antioxidants and polyphenols that further modulate microbial activity and reduce inflammation,” Simmons says.
- Sauerkraut: In an April study published in the scientific journal Applied and Environmental Microbiology, researchers found that sauerkraut had a higher concentration of gut barrier-protective compounds than regular raw cabbage. Specifically, these compounds – which included lactic acid, acetic acid, gamma-aminobutyric acid, phenolic acids, and polyphenols – prevented inflammatory agents from damaging local cells. Besides, sauerkraut is widely available in the US, Dr. Burkhart notes (which isn’t the case for every single entry in this list), so it’s super easy to find in stores should you decide to give it a shot.
- Miso and tempeh: Both of these soy items contain “bioactive peptides with antimicrobial and antioxidant properties,” Simmons says. However, miso differs from tempeh, which is typically cooked and/or pasteurised, in that it also contains the beneficial microbes that produced the peptides in the first place.
- Sourdough bread: While baking snuffs out the lactic acid bacteria that predominate in sourdough, the naturally leavened stuff will retain metabolites like lactic acid, which “inhibits spoilage organisms and potentially pathogenic bacteria,” Simmons says. Translation: It’ll stay fresh for longer and is less likely to give you food poisoning. On the other hand, chemical leavening destroys both the beneficial microbes and the metabolites.
From the sniffles to brittle hair and gum disease.
Last but not least, here’s a fermented beverage to wash any of the above down with.
- Kombucha: Yep, it’s none other than your wellness-obsessed friend’s favourite. Made from fermented green or black tea, kombucha packs “acetic acid, gluconic acid, and tea polyphenols,” all of which help deter pathogens, Simmons says.
All this said, “there's not really head-to-head studies on which ones are better” when it comes to fermented foods, Dr. Burkhart says, so take that into consideration as you’re weighing your options.
Do fermented foods have any health hazards?
Some fermented foods can be high in sodium or sugar (like kimchi and miso or yogurt, kefir and kombucha, respectively), so that can be something to watch out for. Try to choose “unsweetened products whenever possible,” Simmons says. In addition, the fermentation itself can carry inherent risks: “The effects may depend strongly on the individual” based on factors like the state of your existing gut microbiome, your genetics, and your diet, Simmons says. “Not everyone responds the same way.”
Generally, Dr. Burkhart clarifies, fermented foods “provide a lot of benefit, but there are some people who need to approach them with caution” due to the heightened potential for infection, allergy symptoms, and digestive issues.
- First up: immunocompromised individuals – “anybody with a weakened immune system,” Dr. Burkhart says. From a foodbourne illness standpoint, fermented foods may pose more of a danger than most other foods due to the lack of cooking and pasteurisation. Because pasteurization nukes microbes regardless of whether they are good (like probiotics) or bad (like E. coli or salmonella), they are more likely to harbor pathogens. (FWIW, there are no documented US cases of foodborne illness linked to properly fermented foods, according to a review published in the scientific journal Advances in Nutrition in May. Still, if you have low immunity, definitely check with your doctor before digging in, Simmons says.)
- Next is people with a low tolerance for dietary histamine, a chemical compound that plays a key role in allergic reactions. While histamine intolerance is a controversial condition – the American Academy of Allergy, Asthma, and Immunology doesn’t seem to recognise it – people who may be more likely to report symptoms include those who are middle-aged, those with ADHD, and those with myalgic encephalomyelitis/chronic fatigue syndrome (itself controversial). “Histamine levels increase with fermentation, and so people who are sensitive to histamines in foods might experience migraines, rashes, flushing, even respiratory problems if they eat fermented foods,” Dr. Burkhart says.
- Finally, there’s people with digestive disorders such as IBS or small intestinal bacterial overgrowth (SIBO), who tend to have particularly sensitive stomachs. While you might think that fermented foods would offer some degree of relief since they’re known to help counter digestive discomfort, that’s not always the case: In fact, IBS or SIBO sufferers may feel worse when they eat fermented foods “because there's such an imbalance in the bacteria in the gut,” Dr. Burkhart says.
But that isn’t to say that people who have IBS or SIBO need to avoid fermented foods entirely – just that they should handle them with a bit more care. “Start with very small amounts, and maybe don’t have them every day,” Dr. Burkhart advises.
What should you keep in mind when eating fermented foods?
Science doesn’t yet have definitive answers to key questions surrounding this topic, like “How often should I eat fermented foods?” and “What amount should I eat at any one time?,” Dr. Burkhart says (or “What is the target range for the number of microbes I should aim to ingest?,” Simmons adds). In turn, Dr. Burkhart explains, “there really aren't any specific guidelines on how to best consume fermented foods, except to eat them regularly, consistently, and diversely, and to choose ones that are minimally processed.”
That said, Dr. Burkhart has a few basic recommendations: First, try to eat fermented foods once per day – twice if you want to be extra vigilant. That will help facilitate “consistent repopulation of the gut,” she says. Just make sure not to introduce them too fast too soon, as overloading your system could set you up for some digestive distress.
Second, don’t stick to the same foods all the time. “It's always a good idea to eat a variety of different fermented foods if possible, because each of them is going to have a different bacterial population based on the bacteria of the food itself” – a bonus for microbial diversity, Dr. Burkhart says. If you’re buying your fermented foods from the store rather than making them yourself, source from the refrigerated section when applicable, since shelf-stable products won’t contain live probiotics. That "Live and active cultures" label is a reliable tell (or bubbles in a liquid product like kombucha). Given that products that contain live probiotics are also more likely to cause disease, however, keep in mind that you have to weigh that con against the potential pros.
Finally, don’t feel like you have to limit yourself to the fermented foods highlighted in this article. Even though Greek yogurt, kefir, kimchi, miso, tempeh, sourdough bread and kombucha may be some of the biggest names in this space, they’re far from the only options. Besides, the type of fermented food you eat doesn't matter as much as the fact that you're eating a fermented food at all, so choose something that you “are going to enjoy and are going to eat on a regular basis" rather than forcing yourself to choke down something you hate, Dr. Burkhart says. That, more than anything else, will make incorporating fermented foods into your diet sustainable in the long run.
This article originally appeared on SELF.
