Natto, a fermented soy dish, controls blood glucose

When natto is stirred, the soybeans give off a pungent aroma, and fine, sticky strands stretch from the container. Natto is a popular traditional Japanese food known for being nutritious. It’s made by fermenting soybeans with Bacillus subtilis. The bacteria feast on the beans, producing the γ-polyglutamic acid (γ-PGA) that gives natto its gooey, stringy texture. According to research presented by Masuko Kobori, a nutrition researcher at Japan's National Agriculture and Food Research Organization, during a talk in the Division of Agriculture and Food Science on Sunday at the American Chemical Society Fall 2021 meeting, γ-PGA also has health benefits, suppressing blood glucose and insulin levels after a meal.

The researchers measured the γ-PGA levels in various preparations of natto. Stickier natto tended to have higher levels of γ-PGA. Kobori’s team recruited a group of nondiabetic men and women who showed above-average blood glucose levels after eating a bowl of rice. They fed subjects a series of meals consisting of one bowl of white rice plus natto with a high γ-PGA level and one bowl with low γ-PGA natto, then monitored their responses after each meal.

Two hours after eating, subjects who had eaten high γ-PGA natto had significantly lower levels of both glucose and insulin than after they ate the low γ-PGA natto bowl. And even after the low γ-PGA meals, subjects had lower levels of blood glucose and insulin than when they’d eaten a bowl of plain rice (Nutrients 2020, DOI: 10.3390/nu12082374).

Perhaps this health benefit may convince newcomers to give natto a try, Kobori said. Now the researchers hope to study the long-term health impacts of a diet that includes high γ-PGA natto.