Photo/IllutrationA survey found that those who regularly eat “natto” are 32 percent less at risk of dying from a stroke than those who do not. (Asahi Shimbun file photo)

Those who regularly eat “natto” fermented soy beans are about 30 percent less at risk of dying from a stroke than those who don’t, researchers say.

An enzyme called nattokinase, which is contained in natto and effectively prevents blood vessels from clogging up, may help account for the difference, according to Gifu University scholars.

The team questioned 29,000 or so men and women living in Takayama, Gifu Prefecture, in 1992 about their state of health, dietary habits and other facets of their daily lives.

After an interval of 16 years, the team members checked who was still alive and studied the causes of those who died.

The researchers divided the subjects into four groups according to how much natto they normally consumed, and tried to ascertain if there was a correlation between natto intake and the risk of death.

Six hundred and seventy-seven of the subjects were found to have died from a stroke during the study period.

Calculations that eliminated influences of such factors as age, smoking habits and amount of physical exercise showed that those in the group with the largest natto intake (about 7 grams per day, or roughly one or two standard 35-gram portions a week) were 32 percent less at risk of dying from a stroke than those who ate almost no natto.

The risk of dying from myocardial infarction also tended to fall with higher natto consumption. But eating more protein from soy food other than natto, such as tofu and miso, also tended to suppress the risk of death from cardiac infarction.

“You can expect to be able to effectively prevent a stroke and myocardial infarction by eating soy food other than natto as well,” said Chisato Nagata, a Gifu University professor of epidemiology and preventive medicine who was on the research team.

“We encourage people to include a broad range of soy foodstuffs in their everyday meals.”

The team's findings were published in the American Journal of Clinical Nutrition.