Effects of a wholegrain-rich diet on markers of colonic fermentation and bowel function and their associations with the gut microbiome: a randomised controlled cross-over trial

Abstract

BackgroundDiets rich in whole grains are associated with health benefits. Yet, it remains unclear whether the benefits are mediated by changes in gut function and fermentation.ObjectiveWe explored the effects of whole-grain vs. refined-grain diets on markers of colonic fermentation and bowel function, as well as their associations with the gut microbiome.MethodsFifty overweight individuals with increased metabolic risk and a high habitual intake of whole grains (~69 g/day) completed a randomised cross-over trial with two 8-week dietary intervention periods comprising a whole-grain diet (≥75 g/day) and a refined-grain diet (<10 g/day), separated by a washout period of ≥6 weeks. A range of markers of colonic fermentation and bowel function were assessed before and after each intervention.ResultsThe whole-grain diet increased the levels of faecal butyrate (p = 0.015) and caproate (p = 0.013) compared to the refined-grain diet. No changes in other faecal SCFA, BCFA or urinary levels of microbial-derived proteolytic markers between the two interventions were observed. Similarly, faecal pH remained unchanged. Faecal pH did however increase (p = 0.030) after the refined-grain diet compared to the baseline. Stool frequency was lower at the end of the refined-grain period compared to the end of the whole-grain diet (p = 0.001). No difference in faecal water content was observed between the intervention periods, however, faecal water content increased following the whole-grain period compared to the baseline (p = 0.007). Dry stool energy density was unaffected by the dietary interventions. Nevertheless, it explained 4.7% of the gut microbiome variation at the end of the refined-grain diet, while faecal pH and colonic transit time explained 4.3 and 5%, respectively. Several butyrate-producers (e.g., Faecalibacterium, Roseburia, Butyriciococcus) were inversely associated with colonic transit time and/or faecal pH, while the mucin-degraders Akkermansia and Ruminococcaceae showed the opposite association.ConclusionCompared with the refined-grain diet, the whole-grain diet increased faecal butyrate and caproate concentrations as well as stool frequency, emphasising that differences between whole and refined grains affect both colonic fermentation and bowel habits.

Non-invasive VOCs detection to monitor the gut microbiota metabolism in-vitro

“…The release of multiple MCFAs might indicate the concerted action of different microbial groups cooperating in a food breakdown web 38 – 40 . A similar mechanism where MCFAs were released during the anaerobic breakdown of complex organic matrixes by anaerobic cultures was elucidated using time-resolved metatransciptomics by Scarborough et al 38 .Furthermore, the release of MCFAs, as an oat bran signature, has been described in few intestinal fermentation experiments in-vitro and recently reported during an in-vivo intervention 36 , 41 . In general, the possibility to easily monitor and understand the change in VOCs depending on the dietary substrate and donor under study can reveal less-obvious dynamics occurring when studying microbe-diet interactions in-vitro.…”

“…The clustering analysis, which organized VOCs into sub-clusters based on similar time-dependent profiles, highlighted the complexity and substrate-specific nature of these microbial transformations starting from the same microbial inoculum. Furtermore, the clustering of VOCs molecular profiles provides useful information about the system’s molecular behaviour 36 . Grouping molecules with the same time pattern is an indication to understand which molecules can be co-regulated or participate in the same biological processes 37 .…”

Investigating the Crime Scene—Molecular Signatures in Inflammatory Bowel Disease

“…However, dietary fibres are heterogenous compounds, and different fibre types can evoke different biologic responses [ 68 , 102 ]. A wholegrain fibre diet increased the level of butyrate in overweight individuals [ 103 ]. Accordingly, a recent study found that a dietary fibre’s effect depended on the fibre type, the patient immune status and the fermentative capacity of their gut microbiota [ 21 ].…”