Researchers followed 38,981 adults for 16 years (1999-2014) and found that those who ate the most vegetables and the widest variety of vegetables, particularly dark green vegetables, had the lowest rate of heart attacks and heart disease (Nutrition Journal, July 10, 2018;17:67). For more than 60 years, research has shown that a high-fiber diet helps to prevent heart attacks and many other diseases (American Journal of Epidemiology, Dec 1, 1987;126(6):1093–1102). Studies show that many of the impressive health benefits from eating vegetables, beans, whole grains and fruits come from the short chain fatty acids produced when bacteria in your colon ferment soluble fiber from plants.
Short-Chain Fatty Acids from Soluble Fiber
Vegetables, fruits, beans, nuts and whole grains all contain fiber. Insoluble fiber passes through your body without being absorbed into your bloodstream, but breakdown products from soluble fiber can be absorbed even though humans lack the enzymes necessary to digest soluble fiber. Soluble fiber is not absorbed in your upper intestinal tract, so it passes to your colon where bacteria do have the enzymes to break it down into short-chain fatty acids (SCFAs). SCFAs reduce inflammation to help prevent diabetes, heart disease, certain cancers and other life-shortening diseases (Front Microbiol, Feb 17, 2016;7:185).
The Bacteria in Your Gut
Your colon contains more than 13 trillion bacteria that help to control your immunity, digestion and just about everything that happens in our body. You have good bacteria that help to keep you healthy and bad bacteria that can make you sick. As a general rule, the good bacteria are happy to eat the same foods that you do and do not try to invade the cells lining your colon, while the bad bacteria try to invade the cells in your colon. The invading bad bacteria turn on your immunity that tries to kill them and prevent these harmful germs from getting out of your colon and into other parts of your body.
What you eat determines the types of bacteria that thrive in your gut. Soluble fiber in plants promotes the growth of the good bacteria, so when you eat lots of plants, you will have a large colony of these bacteria to convert soluble fiber into SCFAs that have immense health benefits (J Lipid Res, Sept 2013;54(9):2325-40). The good bacteria produce large amounts of SCFAs that feed the more good bacteria and help them to multiply. The SCFAs also:
• reduce inflammation
• help to lower high levels of blood sugar and cholesterol
• possibly reduce hunger
• cause your intestinal linings to produce the beneficial mucous that lines your colon to help prevent the bad bacteria from growing there.
The more vegetables and fruits you eat, the higher the stool levels of SCFAs (Gut, Nov 2016;65(11):1812-1821).
How SCFAs Help to Prevent Disease
Heart Disease: Many studies show that high-fiber diets help to prevent and treat heart disease by reducing inflammation. Your immunity helps to protect you by producing white blood cells and cytokines that kill invading germs when they try to enter your cells. As soon as the invading germ is gone, your immunity is supposed to dampen down. However, if your immunity stays active all the time, it uses the same white blood cells and cytokines to attack your own cells. It can punch holes in the inner lining of arteries to start plaques forming there to increase risk for a heart attack. A constantly active immunity is called inflammation and SCFAs help to reduce inflammation (Nutrients, 2011 Oct; 3(10): 858–876).
Diabetes: After three months on a high-fiber diet, the bacteria in the colons of diabetics changed to be dominated by the 15 known strains of bacteria that convert soluble fiber into SCFAs that lower high blood sugar and cholesterol levels (Science, Mar 9, 2018:359(6380):1151-1156). Diabetics placed on a high-fiber diet had lower fasting blood sugar levels, far lower blood sugars after eating, a greater drop in blood levels of HbA1c that measures cell damage from diabetes, and significant weight loss. Even though fruits are high in sugar, limited amounts of fruit can help to prevent and treat diabetes because their soluble fiber is converted to SCFAs (Diabetes Care, July 2008).
Colon Cancer: A high plant diet is associated with a marked reduction in colon cancer (Epidem Reviews, Jan 1, 1993;15(2):499–545). SCFAs prevent colon cancer in laboratory animals (Mutat Res, Jul-Aug 2009;682(1):39-53). Placing mice on a high-fiber diet that markedly increased SCFAs reduced colon cancer risk by more than 75 percent, but only if the mice had SCFA-producing bacteria in their guts. This study suggests that soluble fiber does not help to prevent colon cancer unless you also have lots of the good bacteria in your gut to convert it to SCFAs (Cancer Discov, Dec, 2014;4(12):1387–1397).
Obesity: SCFAs promote weight loss in animals (Diabetes, 2009 Jul; 58(7):1509–1517) and possibly in humans by decreasing fat storage (J Lipid Res, Sep 2013;54(9):2325-40.)
SCFAs from Plants, not Supplements
If SCFAs have so many benefits, why not just take SCFA supplements? Nobody has shown that SCFA supplements are an effective substitute for eating plants that contain lots of soluble fiber. SCFAs are readily absorbed throughout your entire intestinal tract, so SCFAs in pills will be absorbed in your upper intestinal tract and never reach your colon (PNAS, October 28, 2008;105(43):16767-16772). Therefore, SCFA supplements have not been shown to help colonize healthful bacteria in your colon as soluble fiber in plants does.
This study suggests that whatever else you choose to do with your diet, you should eat a large amount and a wide variety of vegetables. I believe that everyone should eat lots of plants — vegetables, fruits, beans, whole grains, nuts and any other edible plant parts. Among their many benefits, plants help to prevent disease and prolong lives by increasing colonic bacterial production of SCFAs that reduce inflammation.