Oat-Rich Low-Gluten Diet Modulates Plasma Short-Chain Fatty Acids without Significant Changes in Fecal Microbiome or Inflammatory Markers—A Randomized Clinical Trial in People with Cardiometabolic Risk
The Journal of Nutrition, 2026
Mannila E., Gómez-Gallego C., Muluh G., Nuotio P., Koistinen V., Erawijantari P., Salminen S., Lahti L., Kolehmainen M., Linderborg K.
| Disease area | Application area | Sample type | Products |
|---|---|---|---|
Nutritional Science | Pathophysiology | Plasma |  Olink Target 48 |
Abstract
Background
Increasingly popular low-gluten diets (LGDs) are generally low in fiber; however, it is possible to improve the LGD by using oat-based products.
Objective
To investigate the changes in fecal microbiome, fasting plasma short-chain fatty acids (SCFAs), and inflammatory markers during a 6-week oat- or rice-rich LGD in individuals with increased cardiometabolic risk.
Methods
The participants (n=69) were allocated into two parallel groups following a 6-week 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 MetaPhlAn4. Their functional potential was assessed with HUMAnN3 using the MetaCyc database. Plasma SCFAs were quantified by UHPLC-MS, and inflammatory markers were detected and quantified using a 45-cytokine panel (Olink Target). Diet-group differences over time were assessed with linear mixed-effects model.
Results
Dietary information revealed high-oat and low-rice consumption at the baseline for both groups. Overall, the oat-rich LGD increased circulating SCFAs. Particularly, butyrate increased more during the oat-rich LGD than during the rice-rich LGD (ptimeXgroup=0.033). Regarding changes in the fecal microbiome, the rice group had a higher Shannon diversity index after the intervention than the oat group (ptimeXgroup=0.025), and more changes in the microbiome. This is possibly due to more substantial dietary changes from a low rice consumption compared to the habitual diet in the baseline. No significant differences between or changes within the groups in inflammatory markers were observed.
Conclusions
Changing to an oat-rich LGD increases fasting plasma SCFA concentrations without significant effects on the fecal microbiome and inflammatory markers 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 towards potentially unfavorable direction.