How Soluble Fiber Works

Soluble fiber has numerous effects on the body and is one of the best things you can add to your diet. Fruits, vegetables, barley, beans, peas, nuts and seeds are excellent sources of soluble fiber. Oat bran in all its forms, including oatmeal, also contains plenty of the important substance. Most foods with fiber contain a mixture of soluble and insoluble types.

Soluble Fiber in Digestion

When you eat foods with soluble fiber, other components of the food are dissolved and removed in the stomach and small intestines. The soluble fiber cannot be dissolved, but it does absorb water and take on a gel-like consistency. The presence of this thick gel in the digestive tract slows digestion, which gives the intestines more time to absorb nutrients. The soluble fiber gel also pulls in toxins and waste and removes them from the body. Once it reaches the intestines, bacteria ferment the soluble fiber.

Soluble Fiber and Cholesterol

Soluble fiber lowers the level of low-density lipoprotein, or LDL, cholesterol in the blood. This occurs because soluble fiber binds to bile acids, which contain high amounts of cholesterol, in the small intestines. These bound bile acids are eliminated through the bowels instead of being reabsorbed into the bloodstream to release cholesterol. This process also induces the liver to create more bile acids, since those it already created were taken away by soluble fiber. To make new bile acids, the liver must pull even more cholesterol out of the blood stream, lowering LDL levels in the process.

Blood Sugar Effects

Soluble fiber, and the type of fiber called beta-glucan in particular, modulates blood sugar as a result of its viscosity in the digestive tract. As soluble fiber slows digestion, carbohydrates are absorbed and broken down more slowly. The presence of at least 10 percent beta-glucan in cereal foods lowers the glycemic index of those foods by 50 percent, according to a 1997 study in "Diabetes Care." The glycemic index is a measure of how rapidly blood sugar rises in response to consumption of a particular food. Cereals without soluble fiber often have a high glycemic index, meaning that they raise blood sugar quickly, causing a spike in blood glucose.

Effect on Immunity

Soluble fiber boost the immune system by altering the character of immune cells, according to a 2010 animal study in the journal "Brain Behavior and Immunity." Consumption of soluble fiber causes an increase in the production of an anti-inflammatory protein called interleukin-4. An increase in interleukin-4 stimulates an increase in the production of T-cells, the immune cells that fight off infections. In practical terms, this translated to a shorter, less severe illness when the animals in the study who ate soluble fiber were exposed to a bacterial infection. Whether these results are applicable to humans remains to be seen in future studies.

Considerations

Because both soluble and insoluble fiber can change the way food is processed throughout the digestive tract, its a good idea to increase fiber intake gradually, adding just a few grams a day to your diet. The addition of 5 grams per day is a good way to introduce more fiber into your diet.