Modified Japanese diet shows promise for lowering blood pressure, study finds

Can tweaking Japan’s iconic diet beat hypertension? New research shows swapping white rice for whole grains and adding veggies might be the key, without losing cultural roots

Study: Close adherence to the Japanese diet is not associated with a high prevalence of hypertension: The Japan Epidemiology Collaboration on Occupational Health Study. Image Credit: Andrei Iakhniuk / Shutterstock

In a recent article published in the British Journal of Nutrition, researchers examined the association between modified and traditional dietary patterns in Japan, linking diet to hypertension prevalence in 12,213 Japanese workers.

Their findings indicate that while the traditional Japanese diet was not significantly linked to hypertension, following a modified Japanese diet, which contains more whole grains, dairy, raw vegetables, and fruits, showed a suggestive inverse association with hypertension.

Background

An estimated 1.28 billion adults around the world are affected by hypertension, which contributes significantly to stroke and heart disease. Dietary habits, particularly sodium consumption, are linked closely to blood pressure.

This has led health authorities such as the International Society of Hypertension and the World Health Organization to recommend increasing the consumption of vegetables and fruit and reducing salt intake to manage the condition. Global dietary interventions, particularly Mediterranean and Dietary Approaches to Stop Hypertension (DASH) eating plans, appear particularly effective, with regional dietary habits playing an important role.

The traditional Japanese diet, rich in salty foods and relying heavily on ingredients such as miso, soy, fish, and white rice, has been linked to increased blood pressure due to its high sodium content, despite having other positive documented health outcomes. However, salt intake has declined since World War II, with the dietary landscape of Japan shifting to include more Western foods such as fruit and dairy.

About the Study

Researchers examined whether adhering to the traditional diet or a healthier, modified Japanese diet was associated with hypertension among Japanese workers. They applied a cross-sectional or observational study design to data collected from 2018 to 2020 for the Japan Epidemiology Collaboration on Occupational Health (J-ECOH) study.

The study included 12,213 workers (88.1% male, mean age 42.2 years) from five companies who completed a lifestyle questionnaire and a health checkup. People with missing dietary or other covariate data and those with a history of cardiovascular disease or cancer were excluded. Blood pressure was measured during the checkups, and hypertension was noted if the systolic pressure was greater than 140 mmHg, the diastolic pressure was greater than 90 mmHg, or the participant was using hypertensive medications.

Food frequency questionnaires with 28 items were used to assess diet. Researchers used this data to generate two dietary scores, based on the median consumption for each item, with each item being given one point. The traditional Japanese diet score was based on nine items: green tea, salty food, fish, seaweed, mushrooms, vegetables, soy products, miso soup, and white rice. The modified diet score relied on 11 items, adding raw vegetables, fruits, and dairy, reversing the salty food score, and replacing white rice with whole grains.

The researchers used a Poisson regression model to examine hypertension prevalence across different quartiles of dietary adherence, including covariates such as occupational factors, physical activity, smoking, alcohol consumption, and demographics.

Findings

Based on the data from 12,213 workers, researchers compared those who followed modified Japanese diets with those with more traditional eating patterns. Initial analyses suggested that higher adherence to both diets was linked to lower hypertension rates.

However, after confounding variables were included in the model, only the modified diet showed a suggestive inverse association with hypertension (PR for highest vs. lowest quartile: 0.94, 95% CI 0.87–1.01), and the effect of the traditional diet on hypertension became statistically insignificant. Stratified models indicated this inverse relationship was more pronounced in those with fewer than 13 years of education. Among people with lower body mass index (BMI < 23 kg/m²), the traditional diet was positively associated with hypertension.

Conclusions

These findings suggest that the modified Japanese diet, which places greater emphasis on potassium- and fiber-rich foods with lower sodium content, could be better for controlling blood pressure. It may counteract the effects of sodium by promoting sodium excretion and improving nutrient balance.

However, the study found no clear link between hypertension and following the traditional Japanese diet, possibly due to a balance between blood pressure-lowering foods (e.g., vegetables, seaweed) and salty foods. Changes in dietary habits over the years and the relatively younger age of participants (mean 42 years) could explain the weaker effect sizes.

Despite the use of validated tools and a large sample size, the cross-sectional design means that researchers cannot conclude cause and effect. The self-reported nature of the dietary data is another issue, as is the possibility of unmeasured confounding variables. Finally, these findings are not generalizable to other groups drawn from a predominantly male (88.1%) population working for large companies.

Thus, while a modernized Japanese diet could help prevent hypertension while maintaining cultural food practices, further longitudinal studies are needed to confirm these findings.