Forty percent of deaths in the United States are from heart disease, which kills more than 400,000 people each year. Soluble fiber (from beans, oats, peas, barley, nuts, fruits and vegetables) reduces high blood levels of Low-Density Cholesterol (LDL), one of the strongest predictors of heart attack risk (Curr Atheroscler Rep, Dec 2016;18(12):75). Soluble fiber also improves immune function and lowers other risk factors for heart attacks:
• high blood pressure,
• high blood sugar,
• high blood insulin,
• high triglycerides,
• excess body fat (particularly belly fat), and
How Soluble Fiber Lowers Cholesterol
The intestinal tract of humans allows only single molecules to pass through to be absorbed into the bloodstream. You cannot absorb fiber into your bloodstream because it is a long chain of sugars bound end-to-end so tightly that the enzymes in your intestines are unable to separate them.
Fiber is classified into two main types: soluble and insoluble. Insoluble fiber cannot be broken down by humans, so it cannot be absorbed into your bloodstream and it passes from your body undigested. Soluble fiber can be dissolved in water, so although it cannot be absorbed from your upper intestinal tract, it can be broken down by bacteria in your colon into short chain fatty acids that are absorbed through your colon into your bloodstream (Appl Physiol Nutr Metab, June 2015;40(6):535-42).
Soluble fiber is a highly viscous gel that lowers blood cholesterol levels by sticking to bile acids in your intestines to prevent them from being absorbed into your bloodstream. When soluble fiber reaches your colon, it is broken down by bacteria there into short chain fatty acids that are absorbed into your bloodstream through your colon to travel through the bloodstream to your liver where they lower blood cholesterol by preventing the liver from making the bad LDL cholesterol, (Technical explanation: soluble fiber changes one bile acid, cholic acid, to another bile acid, chenodeoxycholic acid, that blocks 3-hydroxy 3 methylglutaryl CoA reductase, an enzyme that makes cholesterol).
How Soluble Fiber Lowers High Blood Sugar and Insulin
The viscous properties of soluble fiber bind to sugar in food to prevent some of the sugar from being absorbed in your upper intestinal tract (J Am Coll Nutr, Feb 2003;22(1):36-42). When soluble fiber reaches your colon, it is broken down by the enzymes from the bacteria there to release some of the sugar. Since blood sugar doesn't rise very much when sugar is eaten with soluble fiber, the pancreas releases far less insulin.
Soluble Fiber Helps to Make You Feel Full
The gel-like properties of soluble fiber prevent many carbohydrates from being broken down and absorbed in your upper intestinal tract. When a meal contains a lot of soluble fiber, the liquid that passes through your intestines is so thick and viscous that it slows contractions of the small intestine to markedly delay digestion of the food in it. Slowed intestinal contractions decrease hunger (Nutr Rev, Feb 2016;74(2):131-47), so a meal that is high in soluble fiber suppresses appetite, increases satiety and reduces the number of calories that you take in (J Am Coll Nutr, 2016;35(1):41-9).
More Evidence of Soluble Fiber's Benefits
The Doctors Study showed that high soluble fiber intake was associated with a 40 percent lower risk of heart attacks (JAMA, 1996;275:447-51), and The Nurses Study showed the same results (Am J Clin Nutr. 1999;69:30-42). Soluble fiber lowered all the markers of high blood sugar levels: blood sugar, insulin, blood pressure, excess weight, belly fat and triglycerides (Diabetes Care, 2004;27:538-46). A diet high in soluble fiber also reduced breast cancer risk (Pediatrics, Feb 2016:137(3);1-11).
How to Increase Soluble Fiber Intake
• All plants and plant parts contain both soluble and insoluble fiber in varying amounts. The more the food is processed, the less fiber it is likely to contain. Good sources of soluble fiber include beans, whole grains, nuts, legumes, snack seeds, fruits and vegetables.
• Eat whole fruits and vegetables instead of juices. Juicing removes most of the soluble fiber.
• Restrict foods made from flour such as bakery products and pastas. Most of the soluble fiber in whole grains is found in the outer coating that is usually milled away and discarded in the flour-making process. Even flour labeled "whole grain" or "whole wheat" is likely to have much of the fiber removed, since manufacturers can use the "whole" label as long as at least 51 percent of the grain is included. You have no way to know how much of the soluble fiber has been removed.
• Among the popular cooked cereals, oatmeal is the richest source of soluble fiber. Other cooked whole grain cereals are also good sources. Most of the dry breakfast cereals are highly refined and less likely to contain much soluble fiber.