Colon Bacteria That Produce SCFAs May Determine Your Susceptibility for Infections

Some of the bacteria growing in your colon may help to protect you from getting infections throughout your body. Researchers cultured stool samples from more than 10,000 people, including more than 600 people hospitalized for serious infections. The stool was specifically checked for 16 types of bacteria that produce Short Chain Fatty Acids (SCFAs). They found that over six years, those who had 10 percent more colon bacteria that produce SCFAs were 15-25 percent less likely to be hospitalized for serious infections (The Lancet Microbe Journal, June 20, 2024). Several previous studies also found that people whose colons have low levels of bacteria that make the SCFAs are at increased risk for serious infections (Front Immunol, May, 2023;14:1186892). Several studies have shown that mice that have large amounts of bacteria that make SCFAs in their colons are at reduced risk for serious infection (Nutrients, May 2022;14(9):1977).

What Are SCFA-Producing Bacteria?
All plants contain soluble fiber that cannot be absorbed in the upper intestines of humans, so when you eat any plant, the soluble fiber passes unabsorbed all the way to your colon, the last five feet of your intestinal tract. Your colon contains more than 100 trillion bacteria, and some of these bacteria are beneficial while others are harmful. The harmful bacteria are not satisfied with the food you eat, so they look for food elsewhere. They try to puncture your colon cells, which turns on your immune system to cause harmful inflammation. On the other hand, the healthful bacteria are happy with what you eat and do not try to puncture your colon cells. These are the bacteria that convert soluble fiber from plants to healthful SCFAs. These SCFAs are absorbed through the colon into the bloodstream where they have already been shown to help lower:
• high cholesterol
• high blood sugar
• high insulin levels
• high blood pressure (Gut Microbiome, May 27, 2023;4 (e11):1-16)
Now we learn that they may even help to protect you from developing infections.

The foods that you eat determine whether you grow healthful or harmful bacteria because healthful colon bacteria eat the same foods that you do (J Lipid Res, Sept 2013;54(9):2325-40). Some foods, such as mammal meat, processed meats, sugar-added foods and fried foods, are known to foster growth of harmful bacteria in your colon. These inflammation-producing foods (“pro-inflammatory foods”) reduce healthful bacteria and increase the harmful bacteria. Anything that promotes bacterial diversity promotes health, while anything that increases inflammation is associated with greater risk for disease.

A plant-based diet helps to keep you healthy. People who eat the most and widest amount of vegetables have 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. SCFAs reduce inflammation to help prevent diabetes, heart disease, certain cancers and other life-shortening diseases (Front Microbiol, Feb 17, 2016;7:185).

The good bacteria produce large amounts of SCFAs that feed 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 mucus 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
SCFAs help to determine whether you:
• become obese (European Congress on Obesity, April 2, 2024)
• have high cholesterol (Cell, April 2, 2024)
• are at increased risk for suffering a heart attack (Int J Mol Sci, 2021 Aug; 22(15): 8074)
• are at increased risk for becoming diabetic (Sci Transnational Med, Oct 25, 2023;15 (719))

Heart Disease: Many studies show that high-fiber diets help to prevent and treat heart disease by reducing inflammation (Nutrients, 2019 May;11(5):1155). Your immune system 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 immune system is supposed to dampen down. However, if your immune system 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 (Int J Mol Sci, 2019 Aug;20(16):3879). A constantly active immune system 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 colon 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).

My Recommendations
Eating lots of fiber-containing plant foods can increase colon SCFA-producing bacteria that may help to reduce susceptibilty for serious infections. The studies cited in this report suggest 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.