【Introduction】
Our previous study found that barley intake improved some subjects' glucose tolerance (responders), but some did not (non-responders).
Responders were characterized by high Prevotella and Prevotella/Bacteroides ratio (P/B ratio) *1. In addition, the P/B ratio of responders tended to be higher at baseline. This study investigated whether it is possible to classify responders and non-responders according to the P/B ratio at baseline.
【Materials and Methods】
In total, this study subjects were 99 healthy men and women with an average age of 64.1 years, an average BMI of 24.3, and an average fasting blood glucose level of 99 mg/dL. 16S rRNA analysis of baseline fecal samples was performed. P/B ratio >1.0 was defined as the high Prevotella group (HP group) and almost zero as the low Prevotella group (LP group). Some subjects had high levels of both Prevotella spp. and Bacteroides spp. and these were defined as the HPB group. After excluding the subjects with fasting blood glucose over 110 mg/dL, with a BMI of more than 30, the number of subjects in each group was 12 (HP group), 13 (LP group), and 8 (HPB group).
In this crossover study, barley bread containing 85% barley and 15% wheat (BKB intervention) or 100% wheat bread (WWB intervention) was consumed for three consecutive days with a washout period of two weeks. The amount of available carbohydrates in the two diets was equal to 100 g/day; resistant starch and total dietary fiber (not including resistant starch) were 14.7 g, 36.4 g for BKB, and 2.7 g, 10.7 g for WWB.
Subjects consumed three portions a day on the first and second days. on the third day, half of the test foods were eaten between breakfast and lunch, and the other half were eaten at 9 pm. The subjects fasted until the following day and ate wheat bread (50 g of available carbohydrate) for breakfast. Blood glucose levels, insulin levels, various gastrointestinal hormone levels, breath hydrogen (H2) levels, the inflammatory cytokine IL-6, and appetite sensations (satiety, hunger and desire to eat) were measured before and after breakfast for 180 minutes. The inflammatory marker CRP was measured only before consumption.
【Results】
The incremental area under the curves (iAUCs) of blood glucose after breakfast was significantly lower after BKB intervention than after WWB intervention in every HP, LP, and HPB group. After BKB and WWB intervention, the AUC was significantly lower in the HP group than in the LP group.
Other measurements and results were as follows.
・After breakfast, the AUC of GLP-1 and GLP-2 in the HPB group was higher after BKB intervention than after WWB intervention. The AUC of PYY in the HP group tended to be higher after BKB intervention than after WWB intervention.
・Breath hydrogen concentration before breakfast was higher in the LP group than in the HP group. In all groups, breath hydrogen concentration after breakfast was higher in the BKB intervention than in the WWB intervention.
・IL-6 was significantly lower in the HP group than in the LP group, and CRP tended to be lower in the HP group than in the LP group. There was no difference between the BKB intervention and the WWB intervention in any group.
・In the LP group, hunger before breakfast was 28% lower, and satiety was 92% higher after BKB intervention than after WWB intervention. After breakfast, hunger and desire to eat were lower in the HP and HPB groups than in the LP group, both after BKB and WWB intervention.
【Discussion and Conclusion】
Regardless of the baseline P/B ratio, barley intake improved glucose tolerance, which improved various cardiovascular, metabolic markers. Interestingly, the baseline P/B ratio affected appetite-related indices and breath hydrogen concentration. HP and HPB groups had lower hunger and desire to eat regardless of the intervention (BKB or WWB). The LP group showed lower desire to eat and higher satiety after BKB intervention. The LP group had significantly higher breath hydrogen concentration during fasting than the HP group, suggesting that the fermentation activity in the intestine was different between the two groups.
The HP group had a better postprandial insulin response (lower AUC of insulin) than the LP group, suggesting that the abundance of Prevotella spp. and higher P/B ratio may help maintain postprandial blood glucose homeostasis.
The BKB intervention improved glucose tolerance regardless of baseline P/B ratio, and the results do not support the hypothesis that the P/B ratio can stratify responders and non-responders who can benefit from the prebiotic effect of barley. However, the possibility that Prevotella spp. may have a significant effect on the effect of dietary fiber fermentation was not ruled out.
In addition, compared to the LP group, the HP group had a better insulin response, lower inflammatory markers, and improved subjective appetite, regardless of the type of intervention. In other words, a higher P/B ratio favors the regulation of the cardiovascular metabolic system, suggesting that it may help prevent obesity, type 2 diabetes, and cardiovascular disease.
【Research institution】
Lund University (Sweden),
University of Gothenburg (Sweden),
University of Copenhagen (Denmark)
*1 Cell Metab 22, 971–82, 2015
Abundance of gut Prevotella at baseline and metabolic response to barley prebiotics
Eur J Nutr 25 Jul 2018
