By Liping Zhao, PhD, scientific advisory board member, AGA Center for Gut Microbiome Research and Education
The gut is not just the organ that digests foods and absorbs nutrients. It also contains a “forgotten organ” — the gut microbiota, i.e., the microbial ecosystem living in the gut. Each person has hundreds of different species of bacteria in his or her gut microbiota. When we eat, we are not just eating for ourselves, but also for our gut bacteria. Anything that is non-digestible or undigested in our diet will be used as nutrients by our gut bacteria. The gut itself also produces nutrients for the gut bacteria, such as mucin or fallen gut cells. Different nutrients will favor different kinds of bacteria.
What we eat can influence the types of bacteria that predominate the gut. We now know that the composition of the gut microbiota can affect human health, so the phrase “you are what you eat” is very true when we realize that our diets are actually culturing a microbial ecosystem in our guts. Gut bacteria can produce various bioactive substances, some of which are beneficial, others harmful. For example, dietary fibers can be used by beneficial gut bacteria to produce a class of compounds called short chain fatty acids (SCFAs). SCFAs can provide energy to our gut cells, reduce gut inflammation and increase our satiety. As a rule of thumb, we don’t take in enough dietary fiber in the modern-day diet. Ten thousand years ago, our ancestors took in 200-400 grams of dietary fiber per day. By comparison, in today’s society, the average person only takes in 10-30 grams.
Any part of the human body can be affected by an unhealthy gut through the circulation of metabolites produced by the gut bacteria. The microbiome has been linked to a variety of symptoms such as constipation, diarrhea, bloating and halitosis. Just as diet may contribute to these symptoms, it could also play a role in reestablishing and maintaining gut health. Manipulating diet as an approach to disease management is an active area of study, along with complementary approaches such as microbiota transplantation, next-generation pro- and prebiotics, and engineered metabolites.
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2. Lam, Y.Y., Zhang, C., Zhao, L. Causality in dietary interventions – building a case for gut microbiota. Genome Med. 2018;10(1):62. https://www.ncbi.nlm.nih.gov/pubmed/30068376
3. Zeevi, D., Korem, T., Zmora, N., et al, Personalized nutrition by prediction of glycemic responses. Cell. 2015;163(5):1079-1094. https://www.ncbi.nlm.nih.gov/pubmed/26590418
This article was featured in AGA Microbiome Update. AGA members — this special microbiome e-newsletter was delivered to your inbox on Tuesday, Aug. 21.