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

Abstract

We evaluated the suppressive effects of high-gamma-polyglutamic acid (γ-PGA) natto on postprandial blood glucose level and insulin response. After confirming the eligibility of candidates using a pre-selective test with packaged white rice, a meal loading test including low- or high-γ-PGA natto (with 57.6 mg (LPGA) and 439.6 mg (HPGA) of γ-PGA, respectively) was conducted in men aged 20 to 70 years (n = 29) and postmenopausal women aged ≤70 years (n = 7). On each examination day, blood samples were obtained after they fasted overnight and for 120 min after test meal loading. The primary outcome of this study was the difference between the measurements of the incremental area under the curve (IAUC) for blood glucose 0 to 30 min after loading of LPGA and HPGA meals. The IAUCs for blood glucose and insulin after the HPGA meal were lower than those after the LPGA meal within 45 min (0 to 15 and 0 to 30 min: p < 0.001, 0 to 45 min: p < 0.01) and 1 h (all p < 0.001) of loading, respectively. The suppressive effects of HPGA natto on postprandial glucose response in the early phase, which possibly relates to the risk of dysglycemia and cardiovascular disease, were clarified.

Untargeted metabolomics revealed the effect of soybean metabolites on poly(γ‐glutamic acid) production in fermented natto and its metabolic pathway

“…11,12 At the same time, γ-PGA has antiobesity functions, lowers blood glucose levels and promotes calcium absorption. 23,24,26 The quality of natto is determined by soybean varieties, fermentation conditions and strains. 38 To date, most studies on γ-PGA fermentation have focused on optimizing growth conditions to increase γ-PGA production.…”

“…γ ‐PGA is an important active substance in the fermentation process of natto and the main component of natto mucus 11,12 . At the same time, γ ‐PGA has antiobesity functions, lowers blood glucose levels and promotes calcium absorption 23,24,26 . The quality of natto is determined by soybean varieties, fermentation conditions and strains 38 .…”

“…[19][20][21]23 In addition, γ-PGA also has activities such as improving obesity and blood glucose levels and has great potential in functional foods. [24][25][26] In L-glutamic acid-independent bacteria, the production of γ-PGA is affected by a variety of fermentation ingredients, such as amino acids, glycerol, glucose, citric acid, glutamic acid, oxalic acid and molasses. 23,[27][28][29][30] Our previous study found that there was a significant positive correlation between the amount of γ-PGA produced by different soluble sugar soybeans.…”

“…In foods, γ ‐PGA can be used as a food supplement, texture enhancer, osteoporosis‐preventing agent, cryoprotectant, bitterness‐masking agent and oil‐reducing agent 19‐21,23 . In addition, γ ‐PGA also has activities such as improving obesity and blood glucose levels and has great potential in functional foods 24‐26 …”

Correlation analysis between soluble sugars of soybean and mucus drawing length of fermented natto

“…The stickiness and drawing properties of natto mucus are due to the strong viscous poly-γ-glutamic acid (γ-PGA) and levan, which have a stabilizing effect (Yoshioka et al, 2007). γ-PGA is the main viscous substance produced during natto fermentation (Araki et al, 2020;Ratha & Jhon, 2018;Nguyen et al, 2018). γ-PGA uses L-glutamic acid and D-glutamic acid as monomers and is a polypeptide polymerized by an amide bond at the γ-position, and its degree of polymerization is between 1000-15000 (Yong et al, 2011).…”