More than 70 percent of North American adults are overweight and almost 50 percent will become diabetic. A new study from China shows that eating more fiber-containing foods encourages growth of bacteria in your colon that can lower high blood sugar levels to normal (Science, Mar 9, 2018:359(6380):1151-1156). Two groups of diabetics were instructed to follow either their normal diet or their normal diet modified with foods that were very high in fiber (vegetables, beans, whole grains and other unground seeds). Both groups also were given acarbose, a diabetic drug (see below).
After 12 weeks, the diabetics who followed the high-fiber diet diet had:
• lower fasting blood sugar levels,
• far lower blood sugar after eating,
• a greater drop in blood levels of HbA1c (a test that measures damage from sugar stuck on cells), and
• significant weight loss.
The researchers cultured the types of bacteria in the subjects' colons before and after the 12 week study period. They found that the diabetics on the high-fiber diet had a marked increase in the 15 strains of bacteria that convert soluble fiber into short chain fatty acids (SCFA) such as buterate, propionate, and acetate, that lower high blood sugar and cholesterol levels. The high-fiber diet also lowered harmful levels in the colon of indole and hydrogen sulfide, that can raise blood pressure and may increase risk for heart attacks (Molecules, Nov 17, 2016;21:1558)
How Short-Chain Fatty Acids (SCFAs) Combat Diabetes and Obesity
You have more than 13 trillion bacteria living in your colon, the last 5 feet of your intestinal tract. The good bacteria stay in your colon and do not try to penetrate the cells lining your colon, but the bad bacteria try to penetrate the cells that line the colon. Your immunity works to kill the bad bacteria before they can escape into your bloodstream. As the bad bacteria keep on trying to get into your bloodstream, your immunity stays active all the time to cause inflammation that can eventually attack your own cells and damage every type of cell in your body. This is why the good bacteria are called anti-inflammatory and the bad bacteria are pro-inflammatory.
The good bacteria produce large amounts of SCFAs that:
• feed them and help the colony to grow,
• turn down inflammation,
• help to lower high blood sugar levels,
• reduce hunger, and
• help to grow the mucous lining your colon, to help prevent the colony of bad bacteria from growing and penetrating the colon walls.
Soluble fiber in many fruits, vegetables, nuts and whole grains is made up of chains of sugar molecules that cannot be broken down by human enzymes. Therefore soluble fiber passes to the colon and fosters the growth of good bacteria that convert soluble fiber to short chain fatty acids that decrease the activity of an overactive immunity and lower high blood sugar and cholesterol. Previous studies have shown that metformin, the most prescribed diabetic drug in the world, lowers high blood sugar levels by also raising colon levels of the good colon bacteria, Bifidobacterium and Akkermansia (Nature Medicine, 2017;23:850–858).
Both groups of diabetics in this study took acarbose, a drug that blocks a natural gut enzyme from breaking down carbohydrates into individual sugars. Humans can absorb only single sugars from carbohydrates. Acarbose prevents a lot of the carbohydrates a person eats from being absorbed into the bloodstream from the stomach and upper intestines and therefore prevents an immediate high rise in blood sugar after eating. Then much of the unabsorbed starches and complex sugars pass undigested to the colon where bacteria break them down so they can be absorbed. These sugars are gradually absorbed in the colon many hours after you eat them and therefore do not cause a high rise in blood sugar.
All foods that are high in fiber help to prevent diabetes, obesity, heart attacks and certain cancers by encouraging the growth of healthful colon bacteria that produce short chain fatty acids that help to prevent these many diseases. Even though fruits can contain a lot of sugar, they are also loaded with soluble fiber so they help to treat and prevent diabetes (Diabetes Care, July 2008). I recommend that diabetics eat whole fruit with meals, even though fruit can raise their blood sugar levels temporarily. However, I recommend avoiding fruit juices because they usually have had all or most of the fiber removed, and they get into your bloodstream very quickly. Fruit juices have been shown to increase risk for diabetes (American Journal of Clinical Nutrition, March 23, 2011) and worsen the course of diabetes in people who already suffer from that disease (The Lancet Diabetes & Endocrinology, June, 2014;2(6):444–446).