You may not be aware of it, but you consume bacteria all the time—they’re all over your food and drinks, from your morning latte to your after-dinner snack. Probiotics, some fermented foods, and prebiotics all contain live microorganisms that influence the composition of your gut microbiome.
An international group of scientific experts has defined probiotics16 as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” Essentially, these are a special class of bacteria that scientists have linked to better health by influencing the composition of the gut microbiome. They can come in the form of pills, powders, or tasty foods and drinks like yogurt and kombucha.
Probiotics are one possible way to change the composition of your gut, but if you test your gut before and after taking probiotics, you might not find a trace of them in your sample. That’s because probiotics may not necessarily colonize your gut even though they influence its composition.
A common misconception is that probiotics and fermented foods are the same thing, but in reality some important differences exist. A fermented food is one that has been transformed by microorganisms; the substrates could include anything from milk (made into yogurt) to meat (made into a dry fermented sausage) to vegetables or beans. Only some fermented foods contain live microbes at the time you consume them; others (like chocolate and coffee) go through processes that kill the microbes after they have done their fermentation work. We cannot measure the exact amount of live microorganisms in fermented foods such as unpasteurized sauerkraut. Their live microorganisms exist in a wild and unmeasured mix. So, while the consumption of such fermented foods certainly influences the composition of your microbiome—as does the consumption of any food—the extent of the influence isn’t consistent.
The newest official definition, published in 2017, states that a prebiotic is simply “a substrate that is selectively utilized by host microorganisms conferring a health benefit.”
This inclusive definition means that the category is going to expand beyond inulin, FOS, and GOS—the three substances traditionally classified as prebiotics. Any substance that improves your health through the way.