Rationale and design of a randomized placebo-controlled nutritional trial embracing a citizen science approach

Modulation of the gut microbiota through specific dietary interventions shows the potential for the maintenance and optimization of health. A dietary fiber diet and fermented foods diet appear to alter the gut microbiota, but evidence is limited. Therefore, we designed the Gut health Enhancement by Eating favorable Food (GEEF) study, a 21-week randomized controlled trial (RCT) studying effects of dietary fibers and fermented foods on gut microbiota diversity and composition, while also stimulating dietary behavior changes through a citizen science (CS) approach. We hypothesized that a high-fermented food diet would increase microbial diversity, whereas a high-dietary fiber diet would stimulate the growth of specific fiber-degrading bacteria. The following elements of CS were adopted: education on the gut microbiota, tailored dietary intervention, remote data collection by participants, sharing of personal gut microbiota outcomes with participants, and vlogs by participants for dissemination of results. Here we describe the study protocol and report the flow of participants, baseline characteristics and compliance rates. Completed in March 2024, the trial included 147 healthy adults randomized to a high-dietary fiber intervention, high-fermented food intervention, or control group. Each group received an additional study product after two weeks: dried chicory root, a fermented beverage, or maltodextrin (placebo). A three-month follow-up assessed the participants’ ability to sustain dietary changes. The recruitment of participants was successful, reflected by 1148 applications. The compliance with the dietary guidelines and study products was >90%. This study shows that including elements of CS in an RCT is feasible and may help recruitment and compliance.