The researchers first took faecal samples from people living in the USA who followed a typical American diet without prescribed dietary restrictions (AMER) (n = 198; including lean, overweight, and three categories of obese subjects) and samples from people living in the USA who followed a plant-rich, calorie-restricted diet with optimized nutrient intake (CRON) (n = 34; including normal-weight subjects) to study the impact of diet on gut microbiota and how the gut microbiota response varies in a context with bacterial dispersal between hosts. Samples were analysed cross-sectionally. Discriminatory features were identified between faecal microbiota samples of CRON and AMER subjects. Subjects who followed a plant-rich and calorie-restricted diet had increased richness and diversity in their gut microbiota and the AMER individuals’ gut microbiota was marked by a lack of many bacterial lineages.
Next, germ-free (gnotobiotic) mice were colonized with the different human donors’ gut communities and fed with either the CRON or AMER diet type. Mice with AMER gut microbiota, which was less diverse, showed a weaker response -consisting of a decreased magnitude of differences in the relative abundances of CRON-associated bacterial taxa such as Bacteroides cellulosilyticus OUT 4020502- to the plant-rich dietwhen compared to their CRON microbiota counterparts.
Finally, the researchers examined whether AMER-colonized mice altered their responses to a CRON diet intervention when cohoused sequentially with mice harbouring the transplanted microbiota of two different CRON donors (thus allowing the exchange of AMER and CRON gut microbial communities). AMER-colonized mice had an improved response to the plant diet that was related to changes in several metabolic features such as leucine, isoleucine and lactate in liver samples.
To sum up, strength of individual gut microbiota responses to diet vary based on prior dietary practices and exposure to a different microbiota in mice can enhance response to diet. Further studies are needed to identify which factors are involved in the exchange of microbes between individuals.
Andreu Prados Andreu Prados holds a Bachelor of Science Degree in Pharmacy & Human Nutrition and Dietetics. Science writer specialised in gut microbiota and probiotics, working also as lecturer and consultant in nutrition and healthcare. Follow Andreu on Twitter @andreuprados