Fiber-Rich Barley Increases Butyric Acid-Producing Bacteria in the Human Gut Microbiota

Abstract

Butyric acid produced in the intestine by butyric acid-producing bacteria (BAPB) is known to suppress excessive inflammatory response and may prevent chronic disease development. We evaluated whether fiber-rich barley intake increases BAPB in the gut and concomitantly butyric acid in feces. Eighteen healthy adults received granola containing functional barley (BARLEYmax^®) once daily for four weeks. Fecal DNA before intake, after intake, and one month after intake was analyzed using 16S rRNA gene sequencing to assess microbial diversity, microbial composition at the order level, and the proportion of BAPB. Fecal butyric acid concentration was also measured. There were no significant differences in diversities and microbial composition between samples. The proportion of BAPB increased significantly after the intake (from 5.9% to 8.2%). However, one month after stopping the intake, the proportion of BAPB returned to the original value (5.4%). Fecal butyric acid concentration increased significantly from 0.99 mg/g feces before intake to 1.43 mg/g after intake (p = 0.028), which decreased significantly to 0.87 mg/g after stopping intake (p = 0.008). As BAPB produce butyric acid by degrading dietary fiber, functional barley may act as a prebiotic, increasing BAPB and consequently butyric acid in the intestine.

Keywords: 16S rRNA gene sequencing; butyric acid-producing bacteria; dietary fiber; microbiota; prebiotics.

Figure 1

Changes in gut microbiota diversity and composition due to the intake of BARLEYmax: (A) numbers of species and Shannon and Simpson indices. (B) principal coordinates analysis plot of Bray–Curtis dissimilarity. Each point represents a sample. The circular, triangular, and square points represent the samples from the pre, post, and one-month groups, respectively. (C) Compositions of the gut microbiota at the order level. Each bar represents an individual sample (left) or a group (right).

Figure 2

Changes in the composition of butyric acid-producing bacteria and fecal butyric acid concentration due to intake of functional barley. (A) Relative abundance of butyric acid-producing bacteria. (B) Concentrations of fecal butyric, propionic, and acetic acids. Points are not connected in the instances of insufficient data.