In recent years, fermented foods have gained great popularity, especially kefir. But do we really know what it is and what distinguishes it from traditional yogurt?
What Is a Fermented Food and Why Is It Beneficial?
Let’s start by clearly understanding what a fermented food is. Fermented foods are those obtained through the growth of beneficial microorganisms. These microorganisms are incorporated into a food matrix and use different components of it to grow. For example, in the case of yogurt, the matrix is milk, and the sugar (lactose) is one of the components the microorganisms use to grow.
Far from being a modern industry “invention,” fermented foods have been with us for thousands of years. Some of them contain microorganisms that are still alive when consumed (such as yogurt, kefir, or tempeh), while in others the microorganisms have been inactivated or removed (bread, fermented vegetables, or soy sauce).
Their consumption has been shown to provide numerous health benefits: they reduce blood cholesterol levels, enhance immune response capacity, protect against pathogens, and reduce the risk of obesity, among others.
These benefits appear to derive from bioactive molecules secreted by fermenting microorganisms during the production process. In addition, since some of these foods contain live microorganisms, they also have probiotic properties.
Kefir and Yogurt: Two Similar Fermented Foods, But Not the Same
Kefir and yogurt are often grouped under the same label of “fermented dairy products,” and it is not uncommon to think that kefir is simply a more liquid yogurt. However, although they share certain characteristics, they are different products, both in their microbial composition and in their effects on health.
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The main difference between yogurt and kefir lies in how they are fermented. Yogurt is produced through lactic fermentation, carried out by the bacteria Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. These microorganisms transform milk lactose into lactic acid, giving yogurt its thick texture and mild, slightly acidic flavor.
Kefir, on the other hand, is produced through a much more complex fermentation process known as lactic-alcoholic fermentation. In this process, not only lactic acid bacteria but also yeasts are involved. As a result, in addition to lactic acid, small amounts of carbon dioxide and ethanol are generated, which are responsible for the presence of bubbles and a minimal alcohol content, usually below 0.5%.
Greater Bacterial Diversity in Kefir
Another fundamental difference is the diversity of microorganisms each product contains. Yogurt hosts a limited number of bacterial strains, making it a very stable and standardizable product, ideal for industrial production. Legal regulations require yogurt to contain at least 10⁷ viable bacterial colony-forming units per gram or milliliter in the final product.
In contrast, kefir grains (the starting culture used in fermentation) contain a more diverse and complex microbial community, ranging from 30 to 50 species depending on their origin. This makes kefir microbiologically more diverse and less uniform.
Recent studies have shown that daily consumption of both yogurt and kefir promotes an increase in the relative abundance of bacteria from the genera Lactobacillus and Bifidobacterium, which are recognized as beneficial for intestinal health.
However, it is important to note that changes in the abundance of beneficial bacteria are temporary and depend on continuous consumption, ideally accompanied by a varied diet rich in prebiotics.
Kefir Is Easier to Digest
In terms of digestion, both products are easier to digest than milk, since part of the lactose is consumed during fermentation. However, kefir usually contains even less residual lactose, which means that many people with lactose intolerance tolerate it better than yogurt.
Finally, regarding micronutrient composition, there are no significant differences in calcium content between yogurt and kefir. Interestingly, vitamin content can vary in both yogurt and kefir during the fermentation process. For example, folate (vitamin B9) levels increase in yogurt due to bacterial synthesis, while cobalamin (vitamin B12) levels do not change.
Kefir vs. Yogurt: Is One Really Better Than the Other?
It cannot be definitively stated that one is better than the other. While yogurt stands out for the stability of its composition, smoothness, and texture, kefir excels in its microbial diversity. However, both provide beneficial microorganisms that can contribute to maintaining a balanced intestinal microbiota and good digestive health.
Since fermented foods offer a very interesting nutritional option, rather than choosing one over the other, it may be more advisable to consume a greater variety. This will enrich the composition of our microbiota while allowing us to enjoy a balanced and diverse diet.
