【Introduction】
Previous studies have shown that diets high in barley beta-glucan (BG) maintain good postprandial blood glucose and insulin response, but the details of its physiological role are unknown. In the present study, we raised mice on a high-fat diet (HFD) containing barley flour with different BG content and examined whether the effects on the metabolic system would be different <Test 1>. In the evaluation system using germ-free mice, intestinal microflora and its metabolite, short-chain fatty acids (SCFA), were also examined <Test 2>. In addition, we confirmed that the effect observed in barley flour was due to BG in a test using cellulose as a control <Test 3>.
【Materials and Results】
<Test 1>
Four-week-old male mice (C57BL/6J) were fed a high-fat diet (60% fat) containing either high BG barley flour or 20% low BG barley flour for 12 weeks, with the former containing 2% of the diet (HBG group) and the latter containing 0.6% of the diet (LGB group). The control group (CO group) was fed a high-fat diet containing no barley flour. The flow of the study, the items examined, and their results are as follows.
(1): Bodyweight: The body weight during the growth period was lower in the HBG group than in the other two groups (P<0.05 compared to the CO group at 13 and 15 weeks of age).
(2): The amount of food intake was significantly lower in the HBG group than in the CO group.
(3): Glucose tolerance test (intraperitoneal and oral): Compared with the CO group, the blood glucose level in the HBG group was significantly lower at 15, 30, and 60 minutes after intraperitoneal loading and at 15 minutes after oral loading.
The HBG group had significantly lower blood glucose levels at 15 minutes of intraperitoneal loading, 30 minutes and 60 minutes of intraperitoneal loading, and 15 minutes of oral loading, compared to the CO group.
(4): White adipocyte adiposity (WAT) and blood tests at autopsy: Compared to the CO group, the HBG group had significantly lower WAT and insulin levels, and higher PYY and GLP-1 levels. There were no significant differences in blood glucose, triglyceride, and leptin levels in the HBG group; there were no significant differences in any of the LBG groups.
(5): In the HBG group, there were significantly rich bacteria from the phylum Actinobacteria, including Bifidobacterium, which is rich in acetic acid-producing bacteria, then in the CO and LBG groups. The ratio of Bacteroidetes to Firmicutes was not significantly different among the three groups.
<Test 2>
In order to confirm whether intestinal bacteria mediate the effect of BG, we conducted the same test by feeding germ-free mice with the same food as the CO group or HBG group. The results showed that body weight, WAT, PYY level, GLP-1 level, food intake, and the amount of SCFA in feces were the same in both groups.
<Test 3>
In order to confirm whether these effects were due to the BG contained in barley flour, we conducted a similar test in 4-week-old male normal mice raised on a high-fat diet containing 5% BG (HFB group) or 5% cellulose (HFC group) for 12 weeks. The HFB group showed significantly higher PYY and GLP-1 levels, lower food intake, and higher fecal SCFA than the HFC group. There was no significant difference in the ratio of Actinobacteria to Bacteroidetes and Firmicutes.
【Discussion and Conclusion】
We found that barley flour with high BG content was suppress appetite and improve insulin sensitivity, preventing increases in body weight and body fat mass. These effects involve gastrointestinal hormones induced by SCFAs produced by intestinal bacteria, and the induction of gastrointestinal hormones by SCFAs is thought to be mediated by the short-chain fatty acid receptors GPR41 and GPR43. The induction of gastrointestinal hormones by SCFAs has also been confirmed in human studies*1, and the results obtained in this mouse study may apply to humans.
The results obtained in this mouse study may apply to humans. 20% barley flour and a high-fat diet containing 5% BG both altered the intestinal microflora of mice, with a significant increase in Actinobacteria, a phylum that produces SCFA by fermenting indigestible polysaccharides*2. The previous human study reported that BGs produced SCFAs by fermentation. In a previous human study, Prevotella spp. was involved in suppressing postprandial blood glucose elevation by consumption of barley bread*3. However, there was no change in the ratio of Bacteroidetes to Firmicutes (including Prevotella). However, there was no change in the ratio of Bacteroidetes (including Prevotella) to Firmicutes. This result may have been due to the more extended period of BG administration in the mouse study and the shorter period of 3 days in the previous human study.
BG has a beneficial effect on the metabolic system through SCFAs and other substances produced by changes in the intestinal microflora. These effects may be the central mechanism of metabolic improvement by barley.
【Research institution】
Tokyo University of Agriculture and Technology (Japan)
Japan Agency for Medical Research and Development (Japan)
Keio University (Japan)
*1 Gut 64(11), 1744-54, 2015
*2 World J Gastrointest Pathophysiol 6, 110–19, 2015
*3 Cell Metab 22, 971–82, 2015
Barley β-glucan improves metabolic condition via short-chain fatty acids produced by gut microbial fermentation in high fat diet fed mice
PLoS One 13, e0196579, 2018
