Most foods contain a mixture of soluble and insoluble fiber, which together make up the dietary fiber family.

Soluble fibers attract water and form a gel, which slows down digestion. Soluble fiber delays the emptying of your stomach and makes you feel full, which helps control weight. Slower stomach emptying may also affect blood sugar levels and have a beneficial effect on insulin sensitivity, which may help control diabetes. Soluble fibers can also help lower LDL (“bad”) blood cholesterol by interfering with the absorption of dietary cholesterol.

Insoluble fibers are considered gut-healthy fiber, because they have a laxative effect and add bulk to the diet, helping prevent constipation. These fibers do not dissolve in water, so they pass through the gastrointestinal tract relatively intact, and speed up the passage of food and waste through your gut. Insoluble fibers are mainly found in whole grains and vegetables. Common types of fiber supplements include psyllium, acacia, guar gum, glucomannan, oat fiber, flax fiber and chia seed.

Health Benefits of Soluble Fiber

Soluble fibers eaten in high amounts can help decrease blood cholesterol. Soluble fiber is also beneficial in moderating levels of blood glucose by slowing glucose absorption from the small intestine. The fiber, such as in oatmeal, is processed slowly and produces a slow increase in blood glucose after eating. This effect may be helpful in the management of diabetes. Additionally, study results suggest that soluble fiber can help delay gastric emptying, which may be useful in preventing overeating because it causes a feeling of satiety.

Soluble fiber provides mass to the stool, helping to ease elimination. The fiber absorbs water and holds onto it in the intestine. When enough fiber is consumed, the water-retaining property helps to enlarge and soften the stool. As a result, less pressure is required to expel the stool.

Health Benefits of Insoluble Fiber

Helps to increase fecal bulk and decrease intestinal transit time, which decreases the risk for diverticulosis, a condition in which small pouches form outside of the intestinal wall and may become infected.

Insoluble fibers are the best fibers for increasing stool size. Bran, which is the fibrous covering of grain kernels, is rich in insoluble fiber. Wheat products are especially beneficial in increasing fecal bulk, while brown rice is useful in decreasing intestinal transit time. A high fluid intake is also important with a high fiber intake to help move the bulk efficiently through the colon.

Both types of fiber serve a major protective function in colon cancer. Researchers hypothesize that carcinogens are diluted by fluid, attracted and bound to the fiber, and then quickly excreted as the fiber passes through the gastrointestinal tract for elimination. Dietary fiber from fruits and vegetables has demonstrated the most protective effect in human studies.


  • Psyllium and other fiber sources high in soluble fiber should not be used within two hours of taking any other supplements or medications; it could delay their absorption into the bloodstream.
  • Psyllium can make tetracycline antibiotics less effective, so consult your doctor for guidance before taking both drugs at the same time.
  • Fiber supplements can temporarily cause bloating and flatulence. To prevent this type of reaction, start with a small amount and gradually increase the dose over several days.
  • Soluble fiber absorbs water, so be sure to take it with large amounts of fluid. Try to drink an additional six to eight glasses of fluid a day while taking fiber supplements. Without a large fluid intake, an intestinal blockage can develop.
  • Do not exceed recommended doses; taking larger quantities of soluble fiber can reduce your body’s ability to absorb certain minerals.
  • If you are pregnant, have diabetes, or suffer from an obstructed bowel (possibly signaled by persistent constipation, absence of bowel movements, or abdominal pain), consult your doctor before taking psyllium preparations.

* These statements have not been evaluated by the Food and Drug Administration. This article is not intended to diagnose, treat, cure or prevent any disease.

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