Can fermented foods improve our health?

We’ve all heard about the amazing health benefits of fermented foods like kimchi, sauerkraut, and kombucha. But is there scientific evidence to back up these claims? This blog post dives deep into the world of fermented foods to separate fact from fiction.

Fermented foods are a delicious and trendy addition to many diets. But more importantly, they may offer real health benefits. This post will help you understand the potential of fermented foods and how to assess the claims you see online.

Sorting through the hype surrounding fermented foods can be confusing. Many studies haven’t been conclusive, and the exact benefits can vary depending on the specific food.

Don’t give up on fermented foods just yet! This post will equip you with the tools to evaluate scientific research and make informed choices. Learn how to spot misleading claims and discover the potential benefits of incorporating fermented foods into your diet.

In this science-based exploration of fermented foods, you’ll gain valuable insights into:

• The difference between probiotics and fermented foods
• The current scientific evidence for health benefits
• Why it’s challenging to study fermented foods
• Tips for evaluating the reliability of online resources

By the end of this post, you’ll be able to navigate the world of fermented foods with confidence and make informed decisions about incorporating them into your diet.

No matter where we land on this journey, please know that I love fermented foods and make and consume them regularly. If you like fermented foods too, feel free to keep eating them regardless of whether or not the current science shows that they confer the drastic health benefits claimed by so many articles on the internet. Also, it’s good to keep in mind that we still have much to learn on this topic, and hopefully, more scientific studies will help us better understand the extent of the health benefits.

Probiotics vs. Fermented Foods

Before we discuss the health benefits, it is essential to clarify the difference between probiotics and fermented foods. Many articles online say fermented foods contain probiotics. But is this statement correct?

The International Scientific Association for Probiotics and Prebiotics brought together a panel of experts in 2013, and they settled on the definition of probiotics. In the published consensus statement, this panel of experts defined probiotics as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” So, the word “probiotics” doesn’t merely mean live and active microbes. 

This definition means that anything called a “probiotic” must satisfy 3 criteria:

1. Are live microbes
2. Are at “adequate” amounts (certain cell counts)
3. Research studies have shown that they confer a health benefit

Based on this definition, it’s difficult for microbial strains to become classified as probiotics. It takes actual research to prove a strain’s probiotic status. Even if that probiotic strain is in your fermented food or assumed to be, you would still have to identify and quantify the microbes to the strain level. It is highly unlikely that you would do this when you are brewing kombucha or making sauerkraut at home. So, those microbes are not, by definition, probiotics.

Kristina Campbell, a science writer who specializes in the area of microbiome research, writing on topics such as fermented foods, microbial therapies, probiotics, and microbes in human health, explains that “essentially, the definition of probiotics means that they have to have been studied. I’m not saying fermented foods are less good, but I’m saying that they’re not always probiotics. I see probably 90% of online articles that mention probiotics say you get probiotics through homemade kombucha and wild-fermented sauerkraut. And that’s not the case, technically.”

If you’d like to learn more about the relationship between probiotics and fermented foods, here are two helpful videos. One is about 3 minutes long, and the other is a little over 30 minutes long and a bit more in-depth.

Evidence of health benefits of fermented foods

Studies in humans have demonstrated some potential health benefits of fermented foods, including decreased risk of type 2 diabetes and cardiovascular disease as well as improved weight maintenance. If you are interested in diving a bit deeper, this review covers many of the latest human studies assessing the potential health benefits of fermented foods.

Though these studies suggest health benefits from certain fermented foods, it is important to note that some of these studies are correlative. This means that the studies do not prove the direct causation of the fermented foods on these outcomes. “A lot of what I have seen has been population evidence where it’s a correlation. This population ate more fermented foods, and they had this difference in health. It’s usually a positive benefit when they find these correlations, but it’s not very strong evidence,” says Campbell.

One type of fermented food that provides a clear health benefit, though, is yogurt. The strains that make yogurt, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus, help with lactose digestion. So, these strains are actually considered probiotics when quantities in the product are known. But some manufacturers add other strains to yogurt. Therefore, it is important to investigate whether the health claims about these additional strains have been validated. 

Unfortunately, though, fermented foods, including yogurt, are not a cure-all. “Eating yogurt has been shown to be beneficial in some instances; however, consuming yogurt is probably not going to solve every problem,” says Dr. Michael Taveirne, who leads a microbiology laboratory class at North Carolina State University that focuses on fermented foods. “Commercials for probiotic yogurts and probiotic pills give the perception that they will benefit everyone and solve a wide variety of issues; however, every person is unique, and many different types of probiotics are on the market. One probiotic may be beneficial for one issue but not another. More research is needed to uncover the specific mechanisms by which bacteria may be helping and to determine which bacteria would be best for each person and each issue.”

When it comes to kombucha, a 2019 systematic review of the published scientific literature found that there has only been one small study on the health effects of kombucha in humans. This one study, which looked at kombucha consumers’ blood sugar levels, was not controlled, meaning it had no placebo group. Therefore, it is not possible to determine whether the kombucha caused the health benefit. The remaining studies that folks base their claims on have been conducted in animals (rats, mice, rabbits, and others) or in cell culture (test tubes). “A lot of the results from these non-human studies gets extrapolated online,” says John Leech, a PhD student who researches fermented foods in Dr. Paul Cotter’s lab. 

So, please take this as a warning. Often the health claims about kombucha are based on non-human studies. And the results in animals and in cell culture do not always play out the same way in humans. 

Overall, we need more human studies to test the effects of specific fermented foods. However, human studies are not simple, to begin with, and they get even more complicated when they involve fermented foods.

Why is it challenging to validate health claims about fermented foods?

When a health claim is made, it must be validated with scientific studies, as discussed above. But the complexity of fermented foods compared to drugs and probiotic pills can be a barrier to testing health claims. “The biggest problem with validating health claims about fermented foods starts with the experimental design,” says Leech. 

Here are a couple of reasons why these human studies to validate the health claims about fermented foods are difficult to design:

1. The batches of fermented foods can vary. “It’s next to impossible to get consistent fermented foods with the exact composition as the previous batch,” says Leech. So, one batch of spontaneously fermented foods (e.g., sauerkraut and kimchi) may produce a benefit because it contains a particular microbial strain. But if the microbial composition of the food differs the next time you make it (i.e., the strain is absent), then you may not see that benefit from the same food.
2. Choosing a placebo is difficult. When you design an experiment, you need to compare the results to a control. In the case of human trials, a placebo is used to determine whether the intervention has an effect. But with fermented foods, “what is the placebo? Is it the same food that’s unfermented (soybeans versus fermented soybeans)? Or is it one with live microorganisms and one with heat-killed microorganisms?” says Campbell. “This is where the study of probiotics comes in because that’s where you can quantify and identify the exact strains, put them in pill form and then test their health benefits compared to a placebo pill. Then you can say that any food with this quantity and dose of strains can confer this health benefit.”

However, the food may be required for the health benefit. “It might be the altered chemistry of the food that provides the benefit, with the addition of metabolites of nutritional value. Or, it could be a mix of both the microbiology and chemistry of the end product,” says Leech. In such a case, a microbial strain may not provide the same benefit in pill form. So, those studies would need to explore the benefit of the fermented foods rather than that of the individual strains. 

How to assess scientific resources

As you can see, this topic is complex. But I believe it is worth understanding. So, I want to equip you with the ability to determine whether or not a resource is trustworthy. These tips apply to any time you need to assess the reliability of scientific resources. And I wanted to provide them here, especially because of the wild health claims constantly circulating in articles online.

“There’s a lot of snake oil out there in the microbiome community. It’s always good to be wary of what people are saying, what benefits they are claiming, and whether they are medically actionable or not. There are some good companies. And then there seems to be a lot of companies that are trying to make a buck off of things without going in-depth on it. It’s always good to be not completely skeptical, but skeptical enough to look behind what you’re buying into,” says Dr. David Baltrus, a microbiology researcher whose lab focuses on the interactions between microbial species.

If you would like to assess the reliability of a scientific resource, you can follow these tips.

1. Look for hedging words (may, seems to, suggests, is possible). When you read about the potential health benefits of probiotics and fermented foods, I want you to look for hedging words. Here’s an example: “may help with irritable bowel syndrome.”  The word “may” indicates that the scientific evidence is not definitive. I want you to be skeptical when an article makes a strong health claim but you don’t see any hedging words. 
2. Go back to the original study(s). See if the claim about a particular food or on the label of the product has scientific evidence to back it up, and assess the quality of scientific evidence, suggests Dr. Baltrus.
   • What/who were the study subjects? Did they do experiments in cell culture (human or animal cells in test tubes), animal models, or with humans? Human studies ultimately provide the information we need to verify claims of health benefits. Studies in mice are not bad. They are simply the first step, and the results might not hold up when tested in humans.
   • What was the experimental setup? Was it a randomized, placebo-controlled study? If so, then you may be able to see causation.
   • What were the effect sizes? Did the study show a significant effect for the claim? How much of a change did they see in the study (small or large effect)?
3. Consider the source of the information. Campbell suggests that you think about the interest of the source. Do they benefit from making you think a certain way? That’s not to say that you shouldn’t read anything that comes from a company—it’s simply worth considering the motive of the source.

When you read about this topic and others regarding health claims, do so with caution. “Caution is the best approach going forward. I am very optimistic about the benefits of fermented foods. But I think caution will certainly be your best friend when you’re reading any internet articles,” says Leech.

Resources

This post contains affiliate links — see my disclosure policy.

As I’ve stressed above, reliable resources are crucial in understanding health claims. So, here are some resources about probiotics, fermented foods, and/or the microbiome that I and/or those that I interviewed recommend.

• The Whole-Body Microbiome: How to Harness Microbes―Inside and Out―for Lifelong Health by B. Brett Finlay, PhD and Jessica M. Finlay, PhD (audiobook)
• I Contain Multitudes: The Microbes Within Us and a Grander View of Life by Ed Yong (audiobook)
• A comprehensive guide to clinical trials
• International Scientific Association for Probiotics and Prebiotics (ISAPP)
• Expert consensus statement about probiotics
• Clinical Guide to Probiotic Products Available in USA (shows the level of clinical evidence supporting the use of specific brands of probiotics for particular health concerns)
• Guide to probiotics from the American Gastroenterological Association
• Probiotics: In Depth from the National Institutes of Health National Center for Complementary and Integrative Health (NCCIH)
• YouTube videos about probiotics: a short one and a longer one

Final Thoughts

I love fermented foods. I make and eat them regularly at home. But whether or not fermented foods provide all of the health benefits that are claimed, as my husband says, “there is nothing wrong with just liking something.” It doesn’t necessarily have to change our health drastically to be beneficial. Fermented foods are delicious and fun to make, and in that way, I think they are highly beneficial. And, in the future, scientific evidence may support more benefits than are currently known.

Making fermented foods at home can also be beneficial in ways beyond the health claims, explains Campbell. We can connect with others in the community, preserve our food and therefore live more sustainably, and enjoy doing something with our hands and then check on our fermented food experiment each day. “When I’m fermenting, I’m bringing something into the world, and it’s changing. It’s very cool,” says Campbell.

Continue Reading the Fermented Foods Series

Thanks so much for reading Part 3 of the Fermented Foods Series. Be sure to check out the rest of the series to learn more about fermented foods!