We share a lot with the people we live with, including the microorganisms that form the communities that inhabit our gut. The level of sharing varies between populations, lifestyles, diets and various other environmental factors, in terms of microbiota composition and diversity. In particular, diet can have a huge bearing on gut microbiota composition, gene expression and its consequent metabolic potential, which in turn affects how we process the food we eat. Even short term changes to our diet can have a significant impact on gut microbiota composition, and certain dietary interventions have shown promise in selecting for beneficial microbial species and promoting gut health. However, whether the same prescribed dietary intervention can have a beneficial impact in individuals with different microbiotas is poorly understood. If only certain microbiotas respond, then the benefits are limited.

A study published in Cell Host & Microbe by Griffin et al., investigated this using two cohorts from the USA with contrasting diets; those who eat a standard American diet (AMER) and those who follow a calorie-restricted diet (calorie restriction with optimised intake of nutrients (CRON)). Germ-free mice were colonised with the gut microbiota from either cohort and fed a specially created diet based on that of either the AMER or CRON groups.

Gut microbiota analysis revealed a variable response to each diet with some microbiota’s being more resistant to diet induced change than others. Mice that were colonised with an AMER microbiota and fed the CRON diet had fewer diet induced changes. Interestingly, AMER mice that were co-housed with CRON mice were more responsive to the CRON diet, and displayed a microbiota and metabolic features more similar to their CRON housemates. This was a result of the increased exchange of CRON-related bacterial species between mice, and the enhanced ability of AMER mice to overcome their reduced bacterial diversity and reconfigure their microbiota to resemble that of CRON mice.

So it seems that diet alone can’t always change your microbiota for the best; you also need the bacterial species associated with these diets to drive the beneficial response. This consequently generates many questions as to how successful prescribed dietary interventions can be for the vast majority, and highlights the need for more research into the range of responses to these proposed interventions. Either that or make sure that your housemate eats healthily to reap the real benefits of a new healthy diet!