"Soluble fiber changes the personality of immune cells - they go from being pro-inflammatory, angry cells to anti-inflammatory, healing cells that help us recover faster from infection," said one of the study authors.

This is because soluble fiber causes increases production of an anti-inflammatory protein called interleukin-4, they said.

Study Details

In the experiment, laboratory mice consumed low-fat diets with either soluble or insoluble fiber. After six weeks on the diet, the animals had distinctly different responses when the scientists induced illness by introducing a substance (lipopolysaccharide) that causes the body to mimic a bacterial infection.

Two hours after this injection, the mice fed soluble fiber were only half as sick as the other group, and they recovered 50 percent sooner. Additionally, after only six weeks, these animals had profound, positive changes in their immune system.

Soluble fiber and Inflammation

The study also found that soluble fiber had a direct anti-inflammatory effect and could offset some of the negative effects of a high-fat diet, essentially immunizing obese persons against the harmful effects of fat.

Obesity is linked to inflammatory conditions, such as diabetes and heart disease, and supplementing a high-fat diet with soluble fiber was linked to reducing this inflammation and therefore protecting against these conditions.

This study is one of the first to show that soluble fiber has direct anti-inflammatory effects and builds up the immune system. It also highlights that the amount of soluble fiber necessary to achieve these health benefits is a reasonable amount.

There are two types of fiber: soluble and insoluble. Insoluble fiber, found in whole wheat and whole-grain products, wheat bran, and green, leafy vegetables, is valuable for providing bulk and helping food move through the digestive system, but it doesn't provide the boost to the immune system that soluble fiber provides.

Good sources of soluble fiber are oat bran, barley, nuts, seeds, lentils, citrus fruits, apples, strawberries, and carrots.

Research Paper Details:

Sherry CL, Kim SS, Dilger RN, et al. Sickness behavior induced by endotoxin can be mitigated by the dietary soluble fiber, pectin, through up-regulation of IL-4 and Th2 polarization. brain Behavior and Immunity, 2010.