New research from the University of California-Davis shows how soluble fiber promotes the growth of healthful bacteria in your colon and discourages the growth of harmful bacteria, to improve your immunity and reduce your chances of suffering heart attacks, infections and some cancers (Science, Aug 11, 2017:357(6351):548-549).
Their research shows that soluble fiber lowers oxygen levels in the linings of the intestines by increasing PPARg (peroxisome proliferator receptor gamma). This reduces the number of harmful bacteria that require high levels of oxygen to survive. The bad germs that try to invade your colon are more active and need more oxygen than the good bacteria that stay in your colon. So a lowered oxygen supply encourages the growth of good bacteria and discourages the growth of the bad ones. The healthful bacteria thrive with less oxygen and break down the soluble fiber into short-chain fatty acids that lower blood cholesterol and help to prevent diabetes and heart attacks.
The Difference between Good and Bad Gut Bacteria Good gut bacteria stay inside your colon, while the bad bacteria try to pass from your colon by boring through your intestinal linings. Your immunity tries to protect you from these invading bacteria by sending out white blood cells and chemicals to destroy them. This defense against the bad bacteria is called inflammation. If your immunity is forced to stay active to kill the invading bacteria in your colon, these same cells and chemicals can attack you. For example, the same chemicals that punch holes in the cell walls of bacteria can punch holes in the inner linings of your arteries to form plaques that can cause heart attacks. The good bacteria don't invade your colon linings and therefore don't turn on your immunity.
How Soluble Fiber Improves Your Immunity Before food can be absorbed from your intestines into your bloodstream, it must be broken down into carbohydrates, fats and proteins. Then carbohydrates must be broken down into single sugars, fats into fatty acids and proteins into their building blocks called amino acids. Your intestinal linings produce enzymes that separate most carbohydrates, fats and proteins into their building blocks that can be absorbed. However, your intestines do not have enzymes that can break down fiber, so it passes through your intestines and reaches your colon intact. In your colon, certain good bacteria have the enzymes that can break down soluble fiber into short chain fatty acids, which can be absorbed into your bloodstream to pass to your liver and lower cholesterol. The new research from UC-Davis shows how eating plenty of foods that contain soluble fiber helps the good bacteria to overgrow the bad ones by depriving them of oxygen. Soluble fiber is found in varying amounts in vegetables, fruits, beans, whole grains, nuts and other edible seeds.
Insoluble fiber is usually not broken down in the colon so it passes through your digestive tract intact and like a broom, sweeps food through your colon to help prevent and treat constipation. More at Soluble and Insoluble Fiber
Colon Bacteria Eat What You Eat Bacteria that try to invade the inner linings of your colon turn on your immunity and are called pro-inflammatory. Bacteria that do not try to invade your colon do not turn on your immunity and are called anti-inflammatory. What you eat determines the types of bacteria that grow in your colon. See Anti-Inflammatory and Pro-Inflammatory Foods. This helps to explain why your health and freedom from disease depend to a large degree on what you eat. Based on the new research, you should make every effort to eat plenty of fruits, vegetables, whole grains, beans, nuts and other seeds.
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