Japan’s population enjoys the longest average lifespan of any country’s: As of 2018, the World Health Organization pegged average Japanese life expectancy at 84.2 years, compared with 78.5 years in the U.S.

Over the course of 28 days, one group ate three daily meals consistent with a modern Japanese diet of today, while the second group adhered to the 1975 diet.

Researchers have long theorized that the traditional eating habits of Japan play a major role in those numbers — and fret that the invasion of Western-style foods will erode the nation’s health.

Studies from Tohoku University took a novel approach to examine the effects of Japan’s changing eating habits: The team re-created typical Japanese meals from 2005, 1990, 1975 and 1960 and fed them to test groups of rodents (both rats and mice bred to age quickly).

The result of experiments in 2016: By the ripe old age of 48 weeks, mice that were fed the 1975 diet displayed the best memory function and lived longest.

Now, the university has extended its tests to human subjects. While people live much longer than mice, the initial results again point to the superiority of Japan’s 1975 diet.

First, the team assembled two groups of moderately obese human subjects age 20 to 70; over the course of 28 days, one group ate three daily meals consistent with a modern Japanese diet of today, while the second group adhered to the 1975 diet.

After the four weeks had passed, the 1975 group’s average body mass index, weight, and waist circumference had dropped, while their evels of LDL (or “bad”) cholesterol and hemoglobin A1C fell, while HDL (“good”) cholesterol rose.

More on dieting and health

Next, the team subjected two groups of non-obese subjects age 20 to 30 to the same regimen.

In this case, the 1975 group demonstrated lower stress and higher fitness after 28 days, along with fewer gut flora associated with disease.

The researchers speculate that the 1975 diet is healthier because it includes a larger number of smaller dishes; less high-heat cooking in oil; less reliance on eggs, dairy products, and meat; and greater use of fermented seasonings instead of salt and sugar.

According to Tsuzuki Tsuyoshi, associate professor with Tohoku University’s Graduate School of Agricultural Science, “The traditional formula for a basic Japanese meal, ‘soup and three,’ helps to guarantee dietary variety.

In practice, this generally means one main dish (frequently fish or another protein) and two side dishes (often vegetables), in addition to rice and soup.”

Here’s a sample menu from the 1975 Japanese Diet, put together by the researchers at Tohoku University:

•June 11, 2019