Soluble fiber improves immune function

March 9, 2010

An article scheduled to appear in the May 2010 issue of the journal Brain, Behavior, and Immunity reports the finding of researchers at the University of Illinois, Urbana that soluble fiber reduces inflammation and strengthens immune function.

University of Illinois College of Medicine professor Gregory Freund and colleagues gave mice low fat diets containing insoluble fiber or soluble fiber from citrus pectin for 6 weeks, after which the animals received an injection of lipopolysaccharide, which elicits the effects of bacterial infection. "Two hours after lipopolysaccharide injection, the mice fed soluble fiber were only half as sick as the other group, and they recovered 50 percent sooner,” study coauthor Christina Sherry reported. “And the differences between the groups continued to be pronounced all the way out to 24 hours. In only six weeks, these animals had profound, positive changes in their immune systems."

Dr Freund explained that soluble fiber increases the production of the anti-inflammatory protein interleukin-4. "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," he noted.

The University of Illinois researchers recently discovered that hormones produced by fatty tissue could help compensate for some obesity-generated inflammation. "There are significant anti-inflammatory components in fat tissue and, if they were strategically unleashed, they could potentially protect obese people from further inflammatory insults, such as a heart attack or stroke,” Dr Freund stated. “In obese animals, you can see the body compensating in an effort to protect itself."

"Now we'd like to find a way to keep some of the anti-inflammatory, positive effects that develop over time with a high-fat diet while reducing that diet's negative effects, such as high blood glucose and high triglycerides,” he remarked. “It's possible that supplementing a high-fat diet with soluble fiber could do that, even delaying the onset of diabetes."

Christina Sherry noted that it is easy to obtain the recommended amount of daily fiber of 28 to 35 grams per day, however, the majority of food labels don’t differentiate between soluble and insoluble fiber. Soluble fiber can be obtained by consuming oats, apples, barley, nuts, seeds, citrus fruits, strawberries, lentils and carrots, or by using powdered supplements.

Immune system strengthening

The impact of aging on the immune system is profound. As people age, a number of critical immune system components are reduced or slowed, including cellular response, response to vaccines, and antibody production. At the same time, susceptibilities to infection and cancer are increased. Some of this increased susceptibility to disease is linked to chronic inflammation, which is associated with many disorders of aging (Ershler WB et al 2000; Hamerman D 1999; Taaffe DR et al 2000).

Although acute inflammation is an important immune system response, chronic inflammation has also been linked to many diseases, including heart disease. Besides the pro-inflammatory cytokines, inflammation may be related to the overproduction of free radicals (Janeway CA et al 1999).

A free radical is an atom or group of atoms (i.e., a molecule) with unpaired electrons. Free radicals are extremely unstable and react easily with other molecules, thereby changing their chemical composition. Oxygen is especially susceptible to free radical formation. The free radicals derived from oxygen are known as reactive oxygen species, or oxidants.

When the body has increased levels of reactive oxygen species (i.e., when it is experiencing oxidative stress), widespread damage may result. At high concentrations free radicals can damage fats, proteins, and nucleic acids. They can also cause cell death, gene mutations, and cancer (Moslen MT 1994). Several diseases may be the result of cellular and genetic damage caused by free radicals, including several immune disorders (Moslen MT 1994).

In order to reduce the damage caused by elevated free radicals and cytokines (which are both part of the natural immune system), the body fights back by producing antioxidants and hormones such as cortisol to suppress the immune system (Grimble RF 1996). Antioxidants are valuable because they pair with unstable free radicals, thereby limiting the damage free radicals can inflict on other cells.