Oat-Rich Low-Gluten Diet Modulates Plasma Short-Chain Fatty Acids without Significant Changes in Fecal Microbiome or...

Increasingly popular low-gluten diets (LGDs) are generally low in fiber; however, it is possible to improve the LGD by using oat-based products.

To investigate the changes in fecal microbiome, fasting plasma short-chain fatty acids (SCFAs), and inflammatory markers (IM) during a 6-wk oat- or rice-rich LGD in individuals with increased cardiometabolic risk.

The participants (n = 69) were allocated into 2 parallel groups following a 6-wk LGD with either oats or rice. Fasting plasma, stool, and dietary information were collected both at the baseline and at the end of the trial. Fecal microbial communities were analyzed by shotgun metagenomics (NovaSeq X Plus) and characterized using metagenomic phylogenetic analysis, version 4 (MetaPhlAn4). Their functional potential was assessed with HUMAnN3 using the MetaCyc database. Plasma SCFAs were quantified by ultra-HPLC-mass spectrometry, and IM were detected and quantified using a 45-cytokine panel (Olink Target). Diet-group differences over time were assessed with a linear mixed-effects model.

Dietary information revealed high-oat and low-rice consumption at the baseline for both groups. Overall, the oat-rich LGD increased circulating SCFAs. In particular, butyrate increased more during the oat-rich LGD than during the rice-rich LGD (P_timeXgroup = 0.033). Regarding changes in the fecal microbiome, the rice group had a higher Shannon diversity index after the intervention than the oat group (P_TimeXgroup = 0.025) and more changes in the microbiome. This is possibly due to more substantial dietary changes from low rice consumption compared with the habitual diet at baseline. No significant differences between or changes within the groups in IM were observed.

Changing to an oat-rich LGD increases fasting plasma SCFA concentrations without significant effects on the fecal microbiome and IM in individuals with increased cardiometabolic risk. When there is a regular baseline consumption of oats, adopting a low-fiber rice-rich LGD may shift the microbiome toward a potentially unfavorable direction. This trial was registered at clinicaltrials.gov as NCT05526092.