We are used to health professionals telling us to include more fibre in our diets, but the old adage ‘too much of a good thing may be harmful’ may ring true here. New research published in the journal Microbiome indicates that high fibre uptake may leave us susceptible to parasitic infections.
The gut microbiome is a complex system that helps us stay healthy, but imbalances within it can lead to dysbiosis and ill health. One of the factors affecting the gut microbiome is diet and, generally, it is believed that incorporating a good amount of fibre in our diet is essential for good ‘gut health’. However, in their recent paper, Laura Myhill and colleagues found that a too high intake of fibre could lead to serious health implications.
They had, in their previous work, shown that inulin fibre diets increased the parasitic burden in parasite-infected mice. This time around, healthy mice were fed a diet that included a high concentration of inulin. This resulted in mice with chronic whipworm (Trichuris muris) infections.
Inulin was thus shown to affect the early part of the immune response to such parasitic infections. Examination of the mice showed that high levels of inulin lead to dysbiosis in the gut microbiome, inflammation of the gut, and increased tryptophan breakdown – all of which detrimentally impacted the immune system's ability to clear the parasite.
When the research team blocked the breakdown of tryptophan, normal immune response was restored. The same thing happened when certain cytokines (IL-18 and IL-27) were neutralised, highlighting how these pathways were important for the host immune response. When inulin was decreased or removed, the mice’s ability to fight infection came back.
The team also found that even if the microbiome composition was unchanged by the inulin diet, the immune response was still impaired. This showed that inulin affects the mucosal lining and the immune response directly and not only via the microbiome.
The exact interaction between the microbiome, the host and the environment are always going to be complex to figure out – after all they evolved together over millennia. But it is clear that high fibre intake can impair response to certain parasites, and this would be an important consideration when advising on the diet of people and animals living in regions where parasitic infections are endemic.