Gut microbial clusters in children show different cardiometabolic responses to wholegrains – a <i>post hoc</i> analysis of a randomized wholegrain trial in children

The beneficial effects of wholegrain intake on cardiometabolic risk may be mediated by the gut microbiota. In adults, cardiometabolic responses appear to be influenced partly by the structure of the gut microbiome ecosystem. However, this has not been investigated in children. We aimed to identify gut microbial clusters among children and explore their role in the cardiometabolic response to high wholegrain intake. The present study utilized data from a previous randomized cross-over study involving 51 Danish 8-13 year-old children with high BMI, provided with wholegrain oats and rye ("WG") and refined grain ("RG") for 8 weeks in random order. Anthropometry, body composition, cardiometabolic markers in blood, and blood and faecal short-chain fatty acids were assessed at 0, 8 and 16 weeks. Faecal microbiota composition was assessed by 16S rRNA gene amplicon sequencing and microbial clusters were identified by partitioning around medoid clustering. We used linear mixed models to investigate the modifying effects of the baseline microbial cluster on the cardiometabolic effects of wholegrain. We identified two clusters dominated by <i>Faecalibacterium</i> (Cluster 1, <i>n</i> = 25), and <i>Clostridium</i> (Cluster 2, <i>n</i> = 26), respectively. Cluster modified the effects of WG on BMI <i>z</i>-score, fat mass index, and waist circumference (all <i>P</i>_interaction ≤ 0.002), which were reduced among children in Cluster 1 and increased in those in Cluster 2. Cluster also modified the effect on HDL cholesterol (<i>P</i>_interaction = 0.03) and tended to modify the effect on faecal butyrate. In conclusion, two distinct gut microbial clusters were identified in schoolchildren, which appeared to affect how effectively a high wholegrain intake reduced fat mass.