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How many microbes are in your body?

Well, almost too many to count. Depending on some outside factors, the number of microbes in your body can range from 30 to 50 trillion. Although all together, those tiny organisms make up a significant portion (1-3%) of your mass, the truth is that they are spread throughout your whole body—even in your eyebrows! Your colon holds the most (1 trillion microbes), followed by about 900 billion in your dental plaque alone! Your oral cavity is also home to several trillions of bacteria in your saliva. All of these microbes are quite mobile, moving between regions of the body and even “hosts” several times. Most importantly, however, they interact with each other to the extent that they are considered to be their own organ. So what does this look like?

Bacteria in your body work with the immune system, the endocrine system, and the digestive system to control immune responses in your body. Their interactive role is so important that severe body dysfunction (i.e. Crohn’s disease, inflammatory bowel disease, gastroesophageal reflux disease) ensues when it is altered too much.

You may be familiar with the gut-brain axis—a very important cross-body interaction influenced by microbes, and one that many people are acutely familiar with, whether they like it or not. Has your digestion ever taken a turn when you were feeling stressed or nervous? Probiotics can stimulate other, more positive, bodily functions, as well: L. paracasei DG, for example, can trigger nutrient production in the colon.

Among the trillions of organisms dwelling in your body, there are an estimated 1,000 different species, each with highly complex DNA. The species composition is constantly changing, however, with the influence of medication, probiotic supplements, and diet. No two people have the same microbiome composition, and it varies throughout organs, which is what makes it so difficult for supplement-seekers to find the right strain. Some species are found more commonly in the colon, some on the skin. The good news, however, is that the population growth of certain strains can aid in the proliferation of others—your microbial “organ” is self-balancing.


The organisms in your body can be categorized in many different ways, but in this instance the focus will be on resident and commensal microbes in the body. Resident microbes (autochthonous) colonize and achieve a stable population in your body. Commensal microbes (allochthonous) require consumption to repopulate in your body. Your resident microbes are often determined genetically, but both types are strongly influenced by environmental factors.

The best way to keep your microbiome healthy is to research what species are most at risk when you take antibiotics, what strains are best for your age group/sex, and to maintain a long-term diverse diet. Studies have shown that plant-based diets are the best for cultivating strains that reduce inflammation and process fiber. Naturally fermented foods will keep up your microflora, as well as probiotic supplements—it is helpful to know what strains you are putting in your body, however, and how much.

When you go to purchase a probiotic supplement, the colony-forming units (CFU count) is often prominently presented on its label. A healthy CFU count is about 1 billion, a number at which the probiotics are nearly guaranteed to make it into your gut and populate there. You probably don’t want to buy supplements with a CFU count lower than this, but any number beyond should be sufficient. What really differentiates probiotic supplements is the strain. Some are generic, some have registered trademarks, some are live and some are “metabiotics.” Some are spores, taken from plants or soil, and some are of human origin.

This may not come as a surprise, but probiotics from plants and soil generally do not occur naturally in your body (although there is some crossover). Spore-based organisms are used as supplements because they do not require refrigeration and their structure helps them to survive the arduous journey from mouth to gut. There is some evidence, however, that the wrong strain at the wrong time can have an adverse effect on the human immune system. Often, strains isolated from humans are much more thoroughly researched before use in a supplement, proliferate less forcefully, and are therefore a little bit more trustworthy. Of course, on the other hand, humans have always been exposed to spore-based organisms by eating fresh fruits and vegetables—the natural way!

Microbes outside of the body are involved in all sorts of things besides keeping humans healthy: the production of alternative fuels, agriculture, nutrient cycles, and gene therapy. According to Ohio State researchers, there are more microbes in a teaspoon of soil than people on Earth. And all of these tiny organisms are constantly working to keep your Earth habitable.

When you are born, your body is quickly colonized by outside bacteria as well as bacteria from your mother. The months and years after birth are very important regarding the buildup of your microbiome. Studies show that these are very formative years for brain development and more, which are influenced by the bacteria you take on.

As you may appreciate, it is important to understand what is happening inside your body—and the microbiome is no exception. Although they’re not widely advertised, knowing about the day-to-day influences probiotic organisms have on your health may help you remediate it! Remember—balance begins within.

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