King's College London

The authors, including Professor Kevin Whelan from the Department of Nutritional Sciences, recommend in a paper published Nature Microbiology that researchers across the globe should collect data on participants’ background diets as part of their future probiotic and prebiotic trials. The group made 10 key recommendations on the design, conduct and reporting of future probiotic and prebiotic clinical trials, including:

• Considering whether, and how, to harmonise the diet of your study population before the intervention.
• Giving precise instructions to participants on the dose and timing of the probiotic or prebiotic substance.
• Scheduling clinical trials to avoid holidays or other times when the dietary intake of the participants may be dramatically different from usual.
• Selecting a dietary assessment method that best answers the research question, for example for short-term or long-term studies.
• Rounding out the research team with a dietitian or nutrition researcher who has experience in dietary assessment and the gut microbiome.

The authors say that by accounting for the influence of diet, researchers may be able to unlock more personalised and effective approaches to improving health through prebiotic and probiotic interventions.

Diet has been overlooked

When studying the health effects of probiotics and prebiotics, researchers often observe significant variation in responses to these gut-targeting interventions, both between individuals and between study cohorts. However, the impacts of variables that account for personalised responses to a probiotic or prebiotic substance are not known.

The authors examined current evidence and found that diet has rarely been incorporated as a variable in research on the efficacy of probiotics and prebiotics.

The experts explain that the current research on food components and the gut microbiome clearly shows how an individual’s diet, especially carbohydrates that are not completely digested in the upper digestive tract such as dietary fibers, affects the availability of substrates for microbial metabolism. These factors shape the gut microbial ecosystem, potentially affecting the success of prebiotic and probiotic interventions.

Evidence from probiotic and prebiotic trials

The paper noted that the small number of probiotic and prebiotic trials to date that have included dietary data show intriguing results, suggesting that the area is promising for further study. For example, in one recent probiotic trial in individuals with metabolic syndrome, dietary characteristics were a key factor that differentiated responders and non-responders. In another study, participants with higher fibre intake in their background diet, had a greater microbiota response and felt fuller while taking a prebiotic supplement than those with lower fibre intake.

Co-lead of the paper Professor Maria Marco from the Department of Food Science and Technology, University of California, said: "Although more studies evaluating the influence diet has in responses to probiotic and prebiotic intake are clearly needed, the totality of evidence from research investigating diet and the gut microbiome strongly indicates that background diet is a major determinant of probiotic and prebiotic efficacy.”

The paper resulted from a workshop convened by the International Scientific Association for Probiotics and Prebiotics (ISAPP) in 2022.