The human gut microbiota has become a novel therapeutic target for treatment of gut disorders. A recent study in New Zealand evaluates whether high or low habitual fiber intake affects the impact of a prebiotic on the gut microbiome.

The human gut microbiota, the population of microorganisms living in our intestines, plays an essential role as part of the human immune system. A perturbed, or “unhealthy”, gut microbiome contributes to gut disorders including metabolic syndromes, liver disease, inflammatory bowel syndrome, and colorectal cancer. Further, diet largely contributes to the abundances and diversity of the microorganisms inhabiting the gut. The gut microbiome has become an attractive therapeutic target for diseases as it plays a critical role in human health and can be conveniently treated by dietary intervention.

The relative abundance of microorganisms and level of microbiome diversity varies significantly between individuals due to factors such as genetics, life stage, geographical location, sex, and use of antibiotics. These factors elicit variable responses to microbiota-targeted therapeutic interventions among individuals. Therapeutics need to be effective, safe, and predictable; therefore, we need to understand factors that influence the human gut microbiome and its responsiveness to intervention.

In a study published in the British Journal of Nutrition, researchers assess how habitual low fiber versus high fiber diets affect the gut microbiota and its response to an inulin-type fructan prebiotic. A prebiotic is an indigestible food product that supports the beneficial microorganisms in the gut. Inulin-type fructan is a type of fiber found in many plants that cannot be digested by the small intestine, so it continues to the lower gut where it is a food source for beneficial gut microbiota. Bacteria convert the prebiotic to short-chain fatty acids that benefit gut health.

In this study, which took place in New Zealand, the researchers were interested in determining how dietary fiber intake influences the gut microbiome and how the gut microbiota responds to inulin-type fructan prebiotic.The study participants were sorted into two groups based on whether they had high or low fiber diets. Each participant received either an inulin-type fructan prebiotic or a placebo every day for three weeks and their responses to this dietary intervention were assessed.

Fiber Intake Predicted Response to a Prebiotic

The researchers found that the gut microbiota responded differently to the prebiotic, and this response was strongly associated with the participants’ fiber intake. The participants with habitual low fiber diets had gut microbiota that was more resilient to change and therefore less responsive to the benefits and side effects of the prebiotic. The gut microbiomes of the participants with habitual high fiber diets experienced significant changes in the relative abundances of many bacterial genera, including the genus Faecalibacterium. The habitual high fiber diet group also experienced increased side effects including moderate flatulence and increased benefits including decreased appetite. Interestingly, the Faecalibacteriumspecies produce butyrate which regulates appetite-associated hormones and carbon dioxide which causes flatulence. This suggests that perhaps the participants with high fiber diets have gut microbiota that are less resilient and therefore the prebiotic has a larger effect.

As demonstrated by this study, it is important to understand how factors including diet, genetics, age, and environment affect an individual’s gut microbiota. The individuals were all administered the same prebiotic, yet the response by the gut microbiota varied depending on the individual’s fiber intake. Future clinical trials should ensure that all factors affecting an individual’s microbiome are considered, as conclusions made from trials may vary depending on the cohort studied. Further, this study demonstrates that it is difficult to predict how the gut microbiota will respond to dietary interventions, and to target the gut microbiota effectively we need to better understand the factors contributing to inter-individual microbiome variability.

Written by Mallory Wiggans

Reference: Healey G, Murphy R, Butts C, Brough L, Whelan K & Coad J. Habitual dietary fibre intake influences gut microbiota response to an inulin-type fructan prebiotic: a randomized, double-blind, placebo-controlled, cross-over, human intervention study. Br J Nutr(2018). 119, 176–189.