Dear Doctors: My boyfriend loves reading about the gut microbiome. He says there’s new information that feeling full after you eat has to do with your gut microbiome. I always thought it was just because your stomach gets filled up with food. Is it actually the gut where feeling full happens?
Dear Reader: We join your boyfriend in being fascinated by the ongoing discoveries about the gut microbiome. For anyone who isn’t yet familiar, the term “gut microbiome” refers to the trillions of microorganisms that make their home in the digestive tract. The vast majority of these -- about 90% -- are bacteria. Other types of single-celled organisms, as well as fungi and viruses, make up the other 10%.
As research into the gut microbiome continues, the scope of its influence on our bodies, and on our bodily functions, becomes increasingly clear. The microflora in our bodies are involved in nutrition, metabolism, physiology and immune function. That means they play a key role in our physical, emotional and mental health.
It has also become evident that the gut microbiome is involved in signaling other organs and areas of the body. This occurs via a mechanism known as the gut-brain axis, which we have touched on in previous columns. And that’s what leads us to your intriguing question about the gut microbiome and hunger.
Feeling full after eating is also known as satiety. As your boyfriend has mentioned, a recent study published in the journal Trends in Endocrinology and Metabolism links these feelings of satiety to the activity of the gut microbiome. It echoes similar findings in previous research, but by highlighting studies that focused on human rather than animal models, this new study adds weight to existing theories that link the gut to satiety.
Research into feeling full after a meal has honed in on small molecules known as short-chain fatty acids, or SCFAs, produced by the communities of microbes living in the gut. These molecules have been shown to play a role in the release of leptin, a hormone that regulates appetite and produces feelings of fullness.
SCFAs are a byproduct of fermentation, which is how our friendly gut microbes “digest” the insoluble fiber in our diets. That’s the fiber that survives the initial process of digestion; it moves into the colon and acts as food for the gut microbiome. This new study identified several additional compounds produced by the gut during fermentation, which also play a role in signaling the brain with feelings of fullness.
More significantly, by focusing on studies in humans, it offers an expanded picture of the digestive process, which includes multiple avenues of direct communication between the gut and the brain. All of this adds to the importance of a diet that is high in quality sources of fiber. By eating from a wide range of fresh vegetables, leafy greens and fruits, you keep your gut microbiome happy and healthy. You also give it the tools to tell the brain that you feel full.
(Send your questions to [email protected], or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
