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Medical review by Elizabeth Gomez, MSN, FNP-BC.
In recent years, both the nutrition research community and dieters have become completely intrigued by the microbiome, the collection of dozens of trillions of microscopic organisms that live in our body. Scientists are still only just scratching the surface of the subject, but many researchers believe that the microbiome has a ton of potential for understanding diabetes and developing new diabetes treatments.
As a result, researchers and amateurs alike are now giving extra scrutiny to the fermented foods we eat, including especially probiotic foods like yogurt, kimchi, sauerkraut, and kombucha, which contain living colonies of potentially helpful microorganisms. These bacteria, fungi, and other tiny organisms have the potential to join and adjust your own microbiome.
There are a lot of folks out there saying that fermented foods can control your blood sugar and keep your weight down. Is there anything to it?
We took a look.
The Tip of the Iceberg
What we found is that the science of diabetes and fermented foods is still fairly sketchy. Here’s some of the latest science on the topic:
- A 2021 Stanford University study showed that fermented foods increase microbiome diversity and decrease inflammatory proteins. Both of those factors have been associated with diabetes risk.
- In 2020, a crew of Brazilian researchers published a review of the existing literature that claimed that “traditional fermented foods can be considered enormous helpers in the complementary and alternative remedy of diabetes, improving mechanisms such as glycemic control, recovery or maintenance of body weight, and antioxidant capacity.”
- A 2018 review performed by a team of Thai researchers determined that fermented foods “significantly reduced the diabetic-associated health complications by increasing the antioxidant capacity and anti-inflammatory machinery” of patients.
While this is encouraging work, it must be said that the scientific case in favor of fermented foods is preliminary, at best, and requires much more learn about. Many reviews of the subject, like this one, admit that we are “just at the tip of the iceberg of understanding the complex interactions” between the microbiome and the human body. It went on to state that of the many investigations that do exist, “the patient numbers are often low, the consequences in part contradictory, and the methodology is varied. ”
It’s also important to note that not all “fermented” products are “probiotic.” Sourdough bread and wine are fermented, but they are not probiotic because the microorganisms that cause the fermentation are killed during the manufacturing process. Yogurt, kimchi, and sauerkraut may or may not be probiotic depending on the product. This makes the subject even more difficult to study, and detracts from the utility of wide-ranging scientific analyses.
Reporting on this topic can also be pretty irresponsible, with headlines often badly inflating the conclusions of scientists. Consider this 2021 article, which claimed in its headline that “fermented foods can help prevent diabetes.” The article covered the Stanford learn about linked above and, well, that’s not quite what the study showed. The study actually argued that a diet high in fermented foods reduced the levels of a particular inflammatory protein, interleukin 6, which “has been linked to” type 2 diabetes (among other conditions). Such a connection may provide a good rationale for designing further studies, but it’s not exactly a smoking gun.
Just as importantly, we’re not aware of any credible claims from members of the diabetes community that fermented foods have immediately recognizable health benefits for people with diabetes. If the probiotic content of sauerkraut or live-culture yogurt had a surprising impression on blood sugar, we would surely notice it on our blood sugar meters and CGMs.
Yogurt & Kimchi
There are also many studies of individual fermented and probiotic ingredients showing similarly encouraging results. I thought I’d take a closer look at a couple of such ingredients, yogurt and kimchi.
- A 2019 study in Nutrients performed a meta-analysis of nine randomized controlled trials on the impact of probiotic yogurt on glucose control. The researchers found zero benefits when compared with conventional yogurt “for improving glucose control in patients with diabetes or obesity.”
- A 2017 review written by food scientists from two American universities found that yogurt “may improve gut health and diminish chronic inflammation by enhancing innate and adaptive immune responses, intestinal barrier function, lipid profiles, and by regulating appetite.”
- A 2017 essay by a team of Spanish nutrition and biochemistry specialists reviewed observational food intake studies, which showed that people that eat more yogurt tend to be healthier and have lower rates of diabetes. But these sorts of studies are notoriously unreliable – they mostly serve as a good way to identify possible associations and guide the design of more robust studies.
As you can see, it’s a mixed bag. Some of the evidence isn’t extremely high quality, and some is conflicting. There’s also the fact that “yogurt” is a very diverse category of products, with very different levels and kinds of probiotic activity. It could be that some types of yogurt are more beneficial than others, but we probably need to await further study before the experts can tease that out.
For the record, strains of probiotics that have been associated with metabolic improvements include L. acidophilus, L. casei, L. rhamnosus, L. bulgaricus, B. breve, B. longum, and Streptococcus thermophilus.
You can find similarly mixed evidence in favor of other popular fermented foods. There are several studies showing that kimchi, for example, has anti-inflammatory and antidiabetic results in rodents. But rodent studies are always just an intermediate step towards studies in humans – they don’t reliably tell us what happens in our bodies.
A 2013 study from Korea assigned 100 healthy young adults to eat kimchi every day for a week. Half of the volunteers ate a very small amount of kimchi (about half an ounce), and half ate a large amount (about half a pound). At the end of this quick experiment, the heavy kimchi eaters enjoyed improvements in cholesterol and fasting blood sugar.
That’s great, but we have no idea if it was the probiotic quality of the fermentation that made the difference. Kimchi is basically flavored and fermented cabbage. Maybe the experiment just shows that it’s a good idea to eat more cabbage. (A different 2013 study showed that fermented kimchi had better metabolic effects than fresh cabbage, but it didn’t measure the same outcomes as the first study.)
Some nutrition experts eagerly recommend fermented foods for a diabetes-friendly diet, not because of the effects of microorganisms, but because they’re otherwise nutritious (and taste great too):
- Cabbage, the main ingredient of both kimchi and sauerkraut, is full of nutrients and fiber.
- Yogurt and kefir are fine sources of calcium and protein (just beware of added sugar in flavored varieties).
- Kombucha is a great low-sugar alternative to soda and fruit juices.
- Tempeh, a fermented soybean product, is a vital high-protein option for plant-forward diners.
You can find studies linking all of the ingredients above to antidiabetic and anti-inflammatory effects. But some of those positive results may be due to the fact that these tend to be healthy ingredients in the first place, even without any probiotic activity.
The Bottom Line
As of today, there isn’t any good evidence that a diet full of fermented foods has a strong effect on the health of people with diabetes. And we are unaware of any credible claims that fermented foods have an immediate positive effect on blood sugar.
But there is quite a lot of encouraging evidence suggesting that fermented foods might have beneficial long-term health effects, possibly by reducing inflammation and strengthening the microbiome. While those effects might be subtle – and still need to be confirmed in trials – they might be seen as a reason to prioritize fermented foods in your diet.
In the meantime, we know that many fermented foods – including yogurt, kimchi, sauerkraut, and tempeh – are healthy choices for people with or without diabetes. Most nutrition authorities recommend including them in a diabetes-friendly diet. If it turns out that they do have subtle antidiabetic effects, we can consider that a bonus.