A Luxembourg Institute of Health’s study has shown how dietary fibres can improve the host’s access to gut microbiome-produced B vitamins, which in turn affect immune function. The findings were published in the journal Microbiome.

Dietary B vitamins, which have numerous health-promoting functions, including immune regulation, are absorbed in the small intestine. Therefore, levels of these compounds in the colon depend entirely on microbial biosynthesis. A new study by the Luxembourg Institute of Health shows how increasing fibre intake can help gut bacteria utilise fewer B vitamins for themselves, boosting the availability of these vitamins to the host. The study, which is under the direction of Professor Mahesh Desai, group leader of Nutrition, Microbiome, and Immunity at the Department of Infection and Immunity, sheds new light on the complex relationship between diet, gut health, and the immune system.

The research team employed various rodent diets with differing fibre contents to explore how these variations affect gut bacteria and, subsequently, host immunity. Their comprehensive analyses revealed that fibre deprivation led to a marked decrease in microbiota-produced B vitamins, a group of vitamins crucial for many bodily functions, including maintaining a strong immune system.

On the other hand, adding either complex cereal fibres or the prebiotic fibre inulin restored the production of these vitamins and restored the balance of the immune system. This occurred because the fibre helped beneficial gut bacteria thrive, while a lack of fibre caused certain bacteria to deplete B vitamins for their own use, leaving less for the host.

Professor Mahesh Desai explained: “Our findings underscore the significant role of dietary fibres in modulating the gut bacteria’s metabolic output, particularly in enhancing the availability of B vitamins. This, in turn, has a profound effect on the host’s immune landscape. Since B vitamin deficiency is associated with a range of diseases, our study highlights the potential for dietary interventions to boost B vitamins in the large intestine and support immune health.”

The study’s results are particularly intriguing given the increasing prevalence of immune disorders and inflammatory diseases. By establishing a clear link between fibre intake, gut bacterial metabolism, and immune function, this research opens new avenues for developing dietary strategies to promote health and prevent disease.

“Dietary fibre is a catch-all term for a very diverse class of carbohydrates,” co-first author Dr Erica Grant noted. “Our research shows that specific types of fibres, like inulin, are more effective in supporting the growth of beneficial bacteria that produce B vitamins, whereas the absence of these fibres creates an environment that drives certain bacteria to utilise B vitamins for themselves.”

“Regarding translational applications in humans,” added Dr Amy Parrish, joint first author of the study, “this could have significant implications for personalised nutrition and the development of targeted dietary interventions to support colonic immune health.”

The study highlights the potential of defined fibre types to boost the production of bacteria-derived B vitamins and regulate local immune populations. These findings pave the way for innovative approaches to using diet to modulate the microbiome and improve immune health.