We have known for a long time that high-fiber foods such as vegetables, fruits and seeds are associated with lower risk for heart attacks, strokes, many cancers, obesity, type 2 diabetes, dementia and other diseases. Now studies on gut bacteria are helping to explain why fiber-rich foods are beneficial. More than 13 trillion bacteria live in your colon and they help to control your immunity in ways that are both helpful and harmful. The helpful bacteria stay inside the colon and do not try to penetrate its lining, but the harmful types of bacteria try to invade the cells on the inner lining of your colon (Cell Host & Microbe, December 21, 2017 ). Researchers at Georgia State University and the University of Gothenburg in Sweden showed that a low-fiber diet decreased the mucous lining the inner colon in mice which allowed the bad bacteria to enter cells lining the inner colon. The types of bacteria in their colons changed significantly, they developed signs of chronic inflammation, they lost much of their ability to respond to insulin, their blood sugars rose and they got fatter. Conversely, feeding the mice a high-fiber diet increased the mucous layer to push bacteria away from the cell walls and reduce inflammation.
How the Bad Gut Bacteria Can Cause Inflammation
Your immunity responds to invading germs by sending out special white blood cells and chemicals called cytokines to kill the invaders. If the bacteria keep on attacking cells lining your colon, your immunity stays active all the time to cause inflammation. These cells and cytokines can attack your own cells throughout your body in the same way that they attack invading bacteria. They can punch holes in the inner linings of arteries that bleed, clot and start plaques forming in arteries to increase your chances of suffering a heart attack. The cytokines that destroy bacteria can also damage the DNA in cells to turn them into cancers. These same cytokines can also block your cells' response to insulin to increase your risk for storing extra fat in your liver that can make you diabetic. See my report on Gut Bacteria Linked to Diabetes
Fiber Nourishes the Good Gut Bacteria
Single sugars are absorbed in your intestines, but you lack the enzymes to break down fiber (long chains of sugars bound together), so it passes unabsorbed through your upper intestines to your colon. There the good bacteria do have the enzymes to break down fiber, and as the bacteria digest the fiber they produce short chain fatty acids (butyrates). Short chain fatty acids help to prevent heart attacks because they are absorbed into your bloodstream and pass to your liver to lower blood levels of the bad LDL cholesterol. They also reduce inflammation because they build up the mucous layer that prevents bad bacteria from getting into the cells lining your inner colon. The good bacteria increase in number when you eat plenty of fiber-rich foods, and this reduces the number of bad bacteria because they have difficulty passing through the mucous to get their food from the cells lining your inner colon.
Other Recent Research on Fiber and Gut Bacteria
• Justin Sonnenberg of Stanford showed that bacteria eat fiber to form short-chain fatty acids that can pass into the bloodstream to reduce inflammation (Nature, 2016 Jan 14; 529(7585): 212–215).
• Hannah D. Holscher, at the University of Illinois, reviewed the scientific literature and found that adding extra fiber to the diet helps people lose weight and lowers blood levels of sugar and insulin (Am J. Of Clinical Nutrition, Nov 1, 2017).
More evidence is accumulating every week to show you that you should eat a fiber-rich diet loaded with fruits, vegetables, whole grains, beans, seeds and nuts, and limit foods that have no fiber (all animal products) or have had the fiber removed (foods made from refined flours and those with added sugars). See my report on Anti-Inflammatory and Pro-Inflammatory Foods. Your gut bacteria eat what you eat, so if you eat a lot of the pro-inflammatory foods you will grow more of the bad types of bacteria, while eating anti-inflammatory foods that have lots of fiber will grow more good bacteria in your colon.