Gut microbiome, prebiotics, and probiotics 101

By Yunzhi Qian, PhD student in Nutrition

Season 23 of “South Park” has an episode called “Turd Burglars,” where one of the characters has a fecal transplant and when it improves her health, all the other women want their hands on her stool. This episode brings fecal transplant and human microbiome to the audience’s attention.

There are trillions of microorganisms that live both inside our bodies and outside on the skin surface. The microbiome is seen as a supporting organ because it plays so many vital roles in promoting the daily operations of the human body. Each person has an entirely unique network of microbiota that is initially determined by genes. A person’s first exposure to the microbiome is during birth delivery from the mother and intake of mother’s breast milk. The infant will have exactly the same microorganisms as the mother. As a child grows, he or she encounters environmental exposure and diet changes, thus changing a person’s microbiome can be both beneficial and harmful to human health. In a healthy person, pathogenic and symbiotic microbiota often coexist. But if there is a disturbance in that balance- caused by diet changes, infectious diseases, or prolonged antibiotics usage, dysbiosis occurs and the normal interaction will be interrupted.

Diet is crucial in determining what kinds of microbiota live in the human intestine. A high-fiber diet is beneficial because it affects the type and amount of microbiota in the colons. Good food sources of fiber include barley, oatmeal, beans, nuts, and fruits. Usually, the more unprocessed the food, the higher the fiber content. Dietary fiber can only be broken down and fermented by microbiota enzymes in the colon. Short-chain fatty acids (SCFA) released from fermentation lowers the pH of chyme (what food is called scientifically after it travels from the stomach to the small intestine), which limits the growth of some harmful bacteria like Clostridium difficile, which can cause diarrhea or inflammation of the intestine. Growing research has also found that SCFA can stimulate immune cell activity and maintain normal blood levels of glucose and cholesterol. On the other hand, a low-fiber diet may not only reduce the amount of beneficial microbiota, but also increase the growth of pathogenic bacteria that thrive in a lower acidic environment.

Prebiotics are a form of dietary fiber that feeds the “friendly” bacteria in your gut. These substances come from types of carbs (mostly fiber) that humans can’t digest. The beneficial bacteria in the gut eat this fiber and help maintain a healthy digestive system. Prebiotics are types of fiber found in vegetables, fruits, and legumes. Some examples include onions, asparagus, bananas, and seaweed.

Sometimes people are confused between prebiotics and probiotics. Probiotics are live bacteria and yeasts that are good for the digestive system. A yummy plain yogurt with live cultures can be a fantastic addition to your diet if you want to add beneficial bacteria. But the yogurt should not be pasteurized, as this process kills the bacteria. Fermented foods like Kimchi and some types of pickles work as well. Probiotic supplement pills are easily found in Costco and other stores, but they do not all have the same types of bacteria or the same concentrations. There are also many products on the market making claims with no proof of efficacy. For a healthy individual, it is better to consume natural food for probiotics compared to supplements.

Peer-edited by Matthew Wang, MS in Human Nutrition candidate

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