Improvement in cardiometabolic risk markers following an oatmeal diet is associated with gut microbiota in mildly hypercholesterolemic individuals

Cardiovascular diseases have been the leading cause of death worldwide for decades. Some animal studies have indicated that oatmeal could improve gut microbiota and cardiometabolic risk markers. However, vivo evidence remained limited, especially in individuals with mild hypercholesterolemia. Our purpose was to explore the beneficial effects of oatmeal on serum lipids, oxidative stress and inflammation levels, and their correlations with gut microbiota and short-chain fatty acids (SCFAs) in mildly hypercholesterolemic individuals. The study was a randomized, single-blind, placebo-controlled trial. A total of 62 qualified participants were randomly divided into control group and oatmeal group with a 45-day follow-up. 16S rDNA and Gas-Chromatography Mass Spectrometry were employed respectively to measure the changes in gut microbiota and SCFAs at the start and the end of the intervention period. Cardiometabolic risk markers were assayed via commercial kits. The results suggested that oatmeal could significantly decrease serum total cholesterol (TC) (-8.59 %, p = 0.013), low density lipoprotein cholesterol (LDL-c) (-12.97 %, p = 0.004) and non-high density lipoprotein cholesterol (non-HDL-c) (-10.98 %, p = 0.040) level. In terms of oxidative stress, oatmeal significantly increased serum total antioxidant capacity (T-AOC) (21.98 %, p < 0.001), superoxide dismutase (SOD) (15.53 %, p = 0.044) levels and decreased concentration of malondialdehyde (MDA) (-19.11 %, p = 0.033) compared with control group. While no significant effect was observed in inflammatory factors. SCFAs results indicated that oatmeal could significantly increase serum acetic acid, propionic acid and valeric acid. The results of 16S rDNA showed that there was a significant difference in the alteration of β-diversity between groups throughout the whole trial. Oatmeal resulted in the increases of Akkermansia, Dialister, Faecalibacterium, Barnesiella, Agathobacter, Lactobacillus and the decrease of Ruminococcaceae-MK4A214-group. Correlation analysis further suggested that the lipids regulation effect of oatmeal may be mainly mediated by Lactobacillus and Dialister, as well as some SCFAs (e.g., acetic acid and propionic acid), while Barnesiella and Akkermansia may play a crucial role in ameliorating oxidative stress level. In conclusion, despite of its small sample size, the present study is the first clinical trial performed in Chinese individuals with mild hypercholesterolemia to explore the effects of oatmeal on serum lipids, oxidative stress, inflammation levels, and gut microbiota. The results demonstrated that oatmeal could induce some beneficial changes in serum lipids, oxidative stress, gut microbiota composition and SCFAs. Correlation analysis further extended our understanding of the role of gut microbiota and SCFAs in improving cardiometabolic risk markers.