We already know that fiber is good for your cholesterol levels and may be protective against colon cancer. Now University of Illinois has studied the effect of fiber, particularly soluble fiber, on its ability to strengthen the immune system.

Fiber, a non-digestible carbohydrate, comes in two forms: soluble and insoluble. The difference between the two is that soluble fiber forms a gel when mixed with liquid, while insoluble fiber does not. This leads to the two types having different effects on the body.

Soluble fiber has the ability to bind with fatty acids, lowering the amount of cholesterol that circulates in the blood. It also provides satiety because it is digested slowly in the stomach, leading us to potentially eat less and lose weight. Soluble fiber can also slow the amount of carbohydrate released into the blood as glucose, so it is beneficial for diabetics as well.

The new study found that soluble fiber reduces inflammation by increasing the production of an anti-inflammatory protein called interleukin-4. This “changes the personality of immune cells,” according to Gregory Freund, a professor at the University of Illinois’’ College of Medicine. “They go from being pro-inflammatory, angry cells to anti-inflammatory, healing cells that help us recover faster from infection.”

Soluble fiber is found in oats and oat bran, dried beans and peas, apples, Brussels sprouts, nuts, barley, flax seed, and psyllium husk. Another benefit of many of the fruits and vegetables high in soluble fiber is their high content of vitamin C — also beneficial for the immune system.

It is difficult to say exactly how much soluble fiber (versus insoluble fiber) is needed to produce the beneficial effects. Most studies have focused on insoluble fiber so far. The recommended daily dietary amount for adults is to achieve a fiber intake of 28 to 35 grams a day. Some studies have shown that most Americans only eat about 14 to 15 grams, primarily because of the used of processed foods and refined flour products.

A diet that consists of at least 5 servings of fruits and vegetables each day plus six servings of whole grains is likely to achieve the amount of both soluble and insoluble fiber needed for positive health benefits.

The National Institutes of Health has a handy tip sheet to use for shopping for foods that are particularly high in soluble fiber.