The Possibility of Suppression of Increased Postprandial Blood Glucose Levels by Gamma-Polyglutamic Acid-Rich Natto in the Early Phase after Eating: A Randomized Crossover Pilot Study

Abstract

The natto containing high levels of gamma-polyglutamic acid (γ-PGA) was recently developed. We investigated the effect of γ-PGA-rich natto consumption on postprandial glycemic excursion in humans. A randomized crossover meal test study was performed on healthy volunteers aged 20–64 years using the following test meals: (1) white rice (WR), (2) low-γ-PGA natto meal (WR + low-γ-PGA natto), and (3) high-γ-PGA natto meal (WR + high-γ-PGA natto). Blood samples were obtained at each visit before and for 120 min after loading. The incremental area under the curve (IAUC) of blood glucose and insulin levels was calculated and compared among the test meals. The blood glucose’s IAUC at 0–120 min, the primary endpoint, was 20.1% and 15.4% lower for the high- and low-γ-PGA natto meal than for the WR, with a significant difference only between the high-γ-PGA natto meal and WR (p < 0.05). The blood glucose’s IAUC at 0–15, 0–30, and 0–45 min was lower for the high-γ-PGA natto meal than for the low-γ-PGA natto meal (all p < 0.05). The possibility that high-γ-PGA natto might suppress blood glucose elevations in the early phase after eating is indicated.

Gamma-Polyglutamic Acid-Rich Natto Suppresses Postprandial Blood Glucose Response in the Early Phase after Meals: A Randomized Crossover Study

“…These criteria were set based on the American Diabetes Association′s cut-off points [ 13 ]. In our previous study, the difference in the effects of the two types of natto may have been reduced because participants with low blood glucose elevation after WR eating were included [ 4 ]. Therefore, this secondary registration test was added in the present study to detect individuals who were not diabetic but had a relatively large elevation in blood glucose after WR loading, prior to undergoing two types of test meal loading tests.…”

“…Next, the IAUCs for blood glucose and insulin were calculated using the trapezoidal method [ 15 ]. The primary outcome was the difference in blood glucose IAUC 0–30 min after the meal between the LPGA and HPGA meals, based on the results of the exploratory study that we conducted previously [ 4 ]. Measures of the IAUC of the blood glucose and serum insulin levels at 0–15, 0–45, 0–60, 0–90, and 0–120 min, and the IAUC of the serum insulin levels at 0–30 min were the secondary outcomes.…”

“…The gamma-polyglutamic acid ( γ -PGA) is a viscous substance produced during the fermentation of natto [ 3 ]. The high- γ -PGA (HPGA) natto showed higher viscosity scores than low- γ -PGA (LPGA) natto in sensory evaluation tests and possible effectiveness of HPGA natto in inhibiting the elevation of postprandial blood glucose within 1 h after a meal was observed in our previous study [ 4 ]. β-glucan, a water-soluble dietary fiber, is a highly viscous substance [ 5 ] similar to γ -PGA.…”

“…In addition, in an interventional study, the peak blood glucose level within 1 h post-loading was considered to be related to the intima-media thickness of the carotid artery (CIMT) [ 11 ]. However, our previous exploratory study [ 4 ] was designed to focus on blood glucose elevations 2 h after eating and had some limitations, such as small sample size, the inclusion of individuals exhibiting a small range of glycemic fluctuations after eating WR because the study participants were selected based on the results of a 75 g oral glucose tolerance test. Additionally, although we avoided setting experimental days during menstruation, there was no consideration of the menstrual cycle in that study [ 4 ].…”

“…However, our previous exploratory study [ 4 ] was designed to focus on blood glucose elevations 2 h after eating and had some limitations, such as small sample size, the inclusion of individuals exhibiting a small range of glycemic fluctuations after eating WR because the study participants were selected based on the results of a 75 g oral glucose tolerance test. Additionally, although we avoided setting experimental days during menstruation, there was no consideration of the menstrual cycle in that study [ 4 ]. It has been suggested that the menstrual cycle affects postprandial blood glucose levels [ 12 ].…”