Can fermented foods help tackle diabetes?

Fermented foods have a long history. Initially, fermenting was a way to keep fresh produce edible for longer, improve flavor, and eliminate toxins. 

Some are researching how fermented foods might influence blood sugar control and type 2 diabetes risk. In this feature, we’ll look at some of these studies. 

Although the evidence isn’t conclusive, there are some promising findings.

What is fermented food?

During fermentation, microbes — like bacteria and yeasts — break down compounds in foods and drinks and convert them into other substances.

For instance, yeast can convert glucose into alcohol. Other microorganisms can convert sugars into organic acids, gases, and other products.

However, some fermented foods are then pasteurized, and this process kills off all microbes. 

Other fermented foods contain microbes that don’t influence your health. So, technically speaking, these foods don't have probiotics.

Some fermented foods may be more familiar than others. Examples include yogurts, cheeses, kimchi, and kombucha. 

To find answers, let’s look at some animal research first.

Although what works in a mouse won’t necessarily work for you, it’s a good place to start. And, so far, there are many more studies in animals than humans.

Animal studies

One study from 2006 used rats with diabetes. The scientists fed them either a placebo or fermented Cordyceps sinensis — a fungus popular in traditional Chinese medicine.

Another study using diabetic rats tested fermented grain. Again, those that had consumed the fermented grain had lower blood sugar levels by the end of the study.

The authors of a similar study investigated a fermented fruit called noni in mice with type 2 diabetes.

The mice that had consumed the fermented fruit had lower blood sugar levels and improved insulin sensitivity than those that had eaten a standard diet or non-fermented noni.

The studies above are just three in the field — many other animal studies show that fermented foods improve blood sugar control in diabetic creatures.

Human studies

So, there’s a fair amount of evidence that fermented products might help lower blood sugar levels in animals with diabetes. But what about research in humans?

These studies are few and far between, but there is some evidence. Let’s start with a traditional Korean side dish of fermented vegetables: kimchi.

Kimchi study

This study recruited 21 people with prediabetes. For the first 8 weeks, participants consumed either fresh kimchi (before fermentation) or fermented kimchi.

After a 4-week break, those who had eaten fresh kimchi switched to fermented kimchi, and vice versa.  

Kefir study

Kefir is a form of fermented milk. This randomized, double-blind, placebo-controlled clinical trial involved 60 people with type 2 diabetes.

Half of the participants consumed probiotic kefir, and the other half consumed conventional fermented milk. Each participant drank 2.5 cups (600 millilitres) twice a day for 8 weeks.

The conventional fermented milk contained Streptococcus thermophiles and Lactobacillus bulgaricus.

The probiotic kefir contained S. thermophiles, too, but it was also enriched with Lactobacillus casei, Lactobacillus acidophilus, and Bifidobacterium lactis.

The authors suggest that the effect would have been even greater if they’d used a control group with a non-fermented beverage. 

They also write that kefir might be a useful complementary treatment for type 2 diabetes.

More on kefir

A review published in 2021 specifically looked at randomized controlled clinical trials of kefir.

In total, they found just six studies that had investigated kefir’s effects on blood sugar control. These included a total of 323 participants.

However, they also call for longer and larger studies — it’s certainly not an open-and-shut case.

What about yogurt?

ZOE has a whole article dedicated to yogurt and diabetes risk. Of all the fermented products, this one has perhaps received the most scientific attention.

Though not all studies agree, the evidence is shaping up nicely overall.

And the authors of a 2016 meta-analysis on the topic write that their conclusions point to a “possible role for dairy foods, particularly yogurt, in the prevention of [type 2 diabetes].”

A 2022 review on type 2 diabetes and fermented dairy in general concluded that evidence of yogurt’s protective effects is the “most consistent.”

However, not all researchers have found a positive effect.

The authors of another review, published in 2019, write, “The present meta-analysis has not demonstrated the benefits of consuming probiotics, compared with conventional yogurt, for improving glucose control in patients with diabetes or obesity.”

Once again, they call for larger studies. Scientists have more work to do. 

Meanwhile, if fermented foods could influence blood sugar control, how would it happen?

How might it work?

Scientists don't yet know whether fermented foods influence blood sugar levels. But they have some ideas. 

These are still only theories, but they’re interesting nonetheless.

Gut microbiome and SCFAs

Fermented foods can influence the makeup of your gut microbiome.

And there’s some evidence from animal studies that they might support gut bacteria that produce short-chain fatty acids (SCFAs).

This is a hormone that encourages your pancreas to release insulin, thereby helping to reduce blood sugar levels.

Calcium

Some scientists think that fermented dairy's calcium content might be important.

This is because calcium levels within cells can influence insulin release. And if calcium influences insulin, it's likely to influence blood sugar levels.

Blocking enzymes

Other scientists think that probiotic dairy products might also block some of the enzymes that chop long carbohydrate molecules into glucose. 

Glucose can only enter your blood once these enzymes have cut it up into simple sugars.

These are just a few of the current theories. It’ll take some unpicking to understand the complex links between probiotic fermented food, gut bacteria, hormones, and blood sugar levels.

What should you do?

At ZOE, we know that adding fermented food to your plate can support your gut health. 

So, if you enjoy the tangy, chili warmth of kimchi or the smooth texture of plain yogurt, adding them to your shopping list is a smart idea.

Although scientists haven’t confirmed whether fermented foods protect against diabetes or influence your blood sugar responses, they’re likely to be a healthy addition to your diet.