【Background】
In previous studies, the suppression of postprandial blood glucose elevation has been confirmed in tests using boiled refined barley grains and barley rice *1 *2. Still, no suppression effect was observed in beverages containing barley β-glucan *3. In these studies, the "second meal effect," in which the effect of suppressing the postprandial rise in blood glucose is seen at the next meal, has been confirmed for both boiled refined barley grains, barley rice, and barley β-glucan added beverages. In other words, the rise in blood glucose immediately after eating barley is thought to be due to the form of barley ingested, and the second meal effect is thought to be largely due to barley β-glucan.
Japanese people often eat bread for breakfast. This study was conducted on Japanese subjects whether barley bread can suppress the postprandial rise in blood glucose and have a second meal effect.
【Methods】
A randomized, double-blind, crossover study of 24 healthy men and women in their 20s, with a washout period of at least 4 days. The subjects consumed barley bread (336 kcal, 2.5 g β-glucan) or wheat bread (282 kcal, 0.19 g β-glucan) with 50 g sugar content for breakfast (first meal) and 180 ml lactose-free milk. Four hours after each meal, the same lunch (second meal, three rice balls, 552 kcal) was consumed. Blood glucose levels were measured before and after each meal (15, 30, 45, 60, 90, and 120 minutes) using a self-monitoring blood glucose meter. The test meals were blinded by adjusting the puffiness of the bread and the appearance of the bread by adding roasted flour. To ensure uniform eating, the crust was removed, and the bread was served in bite-size pieces.
【Results】
On the test day, one of the subjects had a fasting blood glucose level above the threshold for diabetic type (>126 mg/dL), so there were 23 subjects in the primary analysis. Of these, five subjects had fasting blood glucose levels within the borderline range (110-125 mg/dL), so the subgroup analysis was conducted with 18 subjects.
In the main analysis, blood glucose levels after the first meal were significantly lower after barley bread consumption than after wheat bread consumption at 30 minutes after the meal. The area under the blood glucose elevation curve (AUC) tended to be lower after barley bread consumption (P<0.1). Blood glucose levels after the second meal were significantly lower after barley bread than after wheat bread at 60 and 90 minutes after the meal, and AUC was also (P<0.05).
There were no significant differences in blood glucose levels or area under the glycemic curve after the first meal in the subgroup analysis. The significant difference at 30 minutes after the meal in the overall analysis may be due to the effect of borderline subjects with higher peak blood glucose levels. In the subgroup analysis, blood glucose levels after the second meal were significantly lower after barley bread consumption than after wheat bread consumption at 90 minutes after the meal (P<0.05), and AUC was also (P<0.05).
【Discussion and Conclusion】
In healthy Japanese subjects, the effect of barley bread containing 2.5 g of barley β-glucan on suppressing the increase in blood glucose immediately after consumption and the second meal effect was confirmed. In the previous study, these effects were obtained when boiled refined barley was consumed and not when barley gruel or wheat bread added barley fiber was consumed *1.
However, it has been reported that brown rice, which contains mostly insoluble dietary fiber, also suppresses the rise in blood glucose after eating*4. This may be because the dietary fiber surrounding the starch in brown rice interferes with the action of the digestive enzyme alpha-amylase. It is suggested that the effect of dietary fiber on the blood glucose response immediately after a meal is mainly due to the form of food intake.
It has also been reported that barley β-glucan forms complex bound to starch particles *5. Since this bonded state is maintained even after barley is ground into powder, the increase in blood glucose immediately after consumption of barley bread in this study may have been suppressed.
As for the second meal effect, unlike the mechanism of suppressing the rise in blood glucose immediately after eating, it is suggested that the short-chain fatty acids produced by the fermentation of dietary fiber such as barley β-glucan by intestinal bacteria stimulated the secretion of GLP-1, delaying gastric emptying and inducing insulin secretion.
【Research institution】
Hakubaku Co., Ltd.
University of Yamanashi
University of Shizuoka
Yamanashi Gakuin University
*1 Am J Clin Nutr 87,3, 645-54, 2008
*2 Plant Foods Hum Nutr 69, 4, 325–30, 2014
*3 Jpn Pharmacol Ther 20, 1581-7, 2016
*4 Obesity: Dietary Factors and Control 147-57, 1991
*5 Jpn J Nutr Diet 74, 60-8, 2016
Consumption of a meal containing refined barley flour bread is associated with a lower postprandial blood glucose concentration following a second meal than one containing refined wheat flour bread in healthy Japanese: a randomized control trial
Nutrition 72, 110637, 2020
