Dietary fiber, the main food of the gut microbiota, is essential for our health, especially in people whose intestinal microbiota is altered, such as people affected by multiple sclerosis. Among the various properties attributable to dietary fiber is its ability to control the immune system and thus inflammation. However, dietary fiber is very complex as it contains celluloses, hemicelluloses, starches, pectins, inulin, lignins, gums and mucilages, and it is not yet clear which of its different components influences the immune system.
Considering its relevance, it is surprising how few studies have been published on the effect of dietary fiber in multiple sclerosis. Among these studies we would like to highlight one published in 2022 in the prestigious journal Cell Reports (Cell Rep. 2022 Sep 13;40(11):111328) by a group of researchers from the University of British Columbia in Vancouver, Canada, led by Dr. Lisa C. Osborne.
The aim of this study was to compare the effect of different dietary fiber components on neuroinflammation in an animal (murine) model of multiple sclerosis known as experimental autoimmune encephalitis (EAE).
To do this, the researchers fed mice for two weeks with diets containing different amounts of fiber:
- Standard control diet containing 5% dietary fiber.
- Diet without dietary fiber (0%)
- Diet rich in resistant starches (30%)
- Diet rich in inulin (30%)
- Diet rich in pectin (30%)
- Diet rich in guar gum (30%)
Subsequently, they induced the disease, i.e. experimental autoimmune encephalitis, and compared the development of the disease and its severity in the different groups of mice.
Neither lack of fiber, nor diets rich in resistant starches, inulin or pectin had any effect on the development of the disease. However, the guar gum-rich diet did delay the onset of the disease. When comparing the mice that had followed a guar gum-rich diet with the other mice, the researchers found a lower amount of pro-inflammatory lymphocytes in both blood and central nervous system, i.e. brain and bone marrow, in the mice that had followed a guar gum-rich diet, suggesting an effect of this component of dietary fiber on the immune system. Furthermore, in these mice the intestinal microbiota produced more short-chain fatty acids, suggesting an effect of guar gum on the composition of the gut microbiota.
These results should not lead us to the misconception that other fiber components are not beneficial for people affected by multiple sclerosis, as the short time of fiber consumption or the animal model used, which is not identical to the human disease, may have influenced the results. The take-home message is that a diet rich in guar gum may be beneficial while evidence on diets rich in other fiber components is still lacking.
Guar gum is found in a legume that has been produced and consumed for centuries in India and Pakistan. However, in the West, guar gum is used as an emulsifier in the food industry and is therefore present in processed foods. Clearly, if the beneficial role of this fiber component in multiple sclerosis is confirmed, processed food should not be used as a source of guar gum but should be consumed as a supplement or other gums present in dietary fiber with similar properties should be sought.
Despite its limitations, this study is very interesting to understand the complexity and potential of dietary fiber.