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

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.