The differential effect of two cereal foods on gut environment: A randomized, controlled, double-blind, parallel-group study
Background: Cereal foods such as fruit granola (FG) and corn flakes (CF) form part of a fiber-rich diet. Dietary fiber has been reported to improve constipation. In our previous study, it was shown that the consumption of FG for breakfast increases the frequency of defecation. However, changes in intestinal microbiota and intestinal immunity have not been investigated. Methods: In this study, we conducted a randomized, double-blind, placebo-controlled trial to investigate the effects of FG and CF intake on gut microbiota, metabolome, and the immune system. Sixty-eight subjects were randomly divided into two groups, and each group was asked to continuously consume CF or FG for 4 weeks. Blood samples, stool samples, and questionnaires regarding aspects such as defecation frequency were collected before, 2 weeks after, and 4 weeks after intake. Intestinal microbiota was analyzed using 16S rRNA amplicon sequencing. Fecal short-chain fatty acids (SCFAs) were measured using GC-MS, and other fecal metabolomes were analyzed using CE-TOF/MS. Fecal IgA was analyzed using ELISA. Result: The defecation frequency in both the CF group and the FG group was explored. The analysis of the intestinal microbiota showed that there were significant increases in four genera (Bifidobacterium, Subdoligranulum, Ruminococcus 2, and Collinsella) and five genera (Parabacteroides, Mitsuokella, Ruminiclostridium 5, Veillonella, and Collinsella) in the CF and FG groups compared with the baseline, respectively. Three genera (Ruminiclostridium 5, Veillonella, and Collinsella) significantly increased in both the CF and FG group compared with the baseline. On the other hand, four bacterial genera (Lachnospira, Lachnoclostridium, Phascolarctobacterium, and Lachnospiraceae ND3007 group) and three bacterial genera (Dorea, Faecalitalea, and Odoribacter) decreased in the CF and FG groups, respectively. According to the fecal metabolome analysis, 23 metabolites and 19 metabolites significantly increased compared with the baseline in the CF and FG groups, respectively. In addition, 14 metabolites and 22 metabolites significantly decreased in both the CF and FG groups. Furthermore, the analysis showed that the increase in intestinal IgA levels was positively correlated with the concentration of Dialister in CF, whereas in FG, it was correlated with the Lachnospiraceae ND3007 group. Additionally, SCFAs showed a positive correlation with Dialister in the CF group, while they correlated positively with Prevotella 9 in the FG group. Conclusion: This study suggested that the supplement in dietary fiber contained in CF and FG improves bowel movements. In addition, CF and FG each had different effects on the abundance of gut microbes and metabolites and different relationships between fecal IgA or SCFAs and gut microbiota. This may contribute to the future development of personalized food, in which food and fiber are carefully selected to suit the gut bacteria unique to each person.