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By Christian Maino Vieytes, Doctoral Student, The University of Illinois at Urbana-Champaign

The extent of the microbial world is immense. Bacteria, fungi, archaea (single-celled organisms) easily outnumber all organisms of the animal and plant kingdom combined on planet Earth. In humans, each cell we call our own (that is, a human cell) is matched by anywhere from 1 to 10 bacterial cells residing on the human body (1)!

Your Bacterial Self

The hallmark of medical research from the past decade has arguably been the explosion of knowledge gained on the “microbiome. The microbiome refers to all of the non-human cells that reside in the body. These include all bacteria, fungi, viruses, and their genetic information. The microbiome composition is tied to a growing list of health outcomes, including bowel habits, sleep habits, colorectal cancer, cardiovascular disease, and many (many) more(2–4). Thus, taking care of the microbial structures within us has become a focus of the personalized and precision medicine fields (5). This effort takes on several behavioral and environmental modifications. The microbiome is highly dynamic and transient (that is, it shifts throughout the day, week, seasons, etc.!) and responds well to interventions.

Prebiotics and Diet

Perhaps the most important of those interventions is diet (6). The research has been quite coherent and consistent in demonstrating that eating a greater variety of plant-based foods high in fiber increases microbial diversity in the gut. In turn, greater diversity decreases the risk of several inflammatory diseases, such as inflammatory bowel disease and cancer. In contrast, higher consumption of animal-based foods decreases microbial diversity and selects for microbes that promote inflammation and elevate the risk of inflammatory conditions (7–9). The underlying principle of how we eat shapes our microbial self is defined by prebiotics. Prebiotics are the foods we eat that are shared with microbes living in our gut. By natural selection, only those microbes that can survive on the food we feed them will thrive, while those who cannot die off eventually. Thus, we shape the composition of our microbiome by “selecting” the kinds of microbes with the food we eat.


Now, let us shift to a similar yet distinct concept. Another concept in the field of nutrition with rising popularity is the advent of probiotics. Unlike prebiotics, which is fuel for the microbes living in our gut, probiotics are actual living or inactive microbes (typically bacteria or fungi) that humans consume with the purpose of changing the microbial composition in their gut.

(10). Probiotics may be taken in a supplement form or found in foods enriched with microorganisms that produce an effect on our gut microbiome.

Examples of foods include:

  • Kimchi
  • Tempeh
  • Fermented milk/yogurt
  • Miso
  • Sauerkraut
  • Kombucha
  • Natto (is a traditional Japanese dish consisting of fermented )

A hallmark of probiotic foods is their origin or preparation, either of which will involve some aspect of fermentation. Hence, this is why fermented foods have been touted as probiotics by food developers.

Health Effects of Probiotics

A defining feature of probiotics and what sets them apart from prebiotics is that they only produce an “acute” effect on the gut. They must be consumed regularly for the probiotic strains to thrive within the gut. Nonetheless, they share many health benefits similar to those seen with eating a healthy, fiber-rich diet. Probiotic supplementation has been shown to reduce levels of inflammation in the body (11). Inflammation, as you may recall, is a contributor to overall health and disease. Maintaining low levels of inflammation may lower the risk of several conditions, including cardiovascular disease. LDL cholesterol, which is a risk factor for the condition, was shown to be reduced with 8-weeks of a probiotic supplement program in overweight individuals (12). Additionally, probiotics may play some role in warding off inflammatory bowel disease from taking hold in an individual (13). Though evidence of probiotics’ effects on health outcomes remains limited, the case is stronger for the role of probiotics in reducing the frequency and effects of constipation and diarrhea (14,15).


We know that diet plays a significant role in shaping our bodies and our health. New science on the microbiome highlights how a third factor, the community of microbes living on us, is also informed by our diet and lifestyle behaviors. Eating a diet rich in fruits, vegetables, and whole grains is the principal approach to “select” for a healthier composition of microbes in our bodies. However, consuming foods typically of fermented origin rich in microbes may also benefit overall well-being. Indeed, these “probiotic” foods have been shown to extend benefits to humans. Nevertheless, we should also recognize that consuming probiotic supplements or foods is not a substitute for a well-balanced diet rich in plant foods when it comes to health. 


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