Food things you should know

As the global population ages, cognitive decline and the increase in the number of people with dementia are closely related to global health, and more and more studies have shown that changes in lifestyle and eating habits can help improve brain degeneration. A study in the Journal of Nutrition in April 2024 pointed out the positive relationship between traditional Japanese diet and improving brain atrophy, and the effect was particularly evident in women.

Written by Hao Zhiqi

Cognitive decline and dementia already affect more than 55 million people worldwide, a number that is expected to rise rapidly in the coming decades as the global population ages. While these diseases are sometimes caused by genetic factors, a growing body of research suggests that the risk of dementia can be managed through lifestyle changes, such as quitting smoking, weight control, and regular exercise. As a result, the role of nutrient intake in preventing cognitive decline and dementia has become a focus of scientific research. For example, many studies have found that the Mediterranean diet may have a positive impact on brain health, such as total brain volume, cortical thickness, and white matter integrity. Therefore, the search for healthier ways to eat is closely related to improving global health.

Is the secret to Okinawa residents' longevity derived from traditional Japanese diet?

A study published in the Nutrition Journal in April 2024 found that the traditional Japanese diet helps reduce brain shrinkage, and this effect is particularly prominent in women. This result is not surprising, because Japan has always been famous for its longevity. Take Okinawa Prefecture in Japan, for example, there are many centenarians in the area, so Okinawa is recognized as a "blue zone" where residents have unusually long lifespans. The longevity of Okinawa residents is often attributed in part to their traditional diet.

The typical Japanese traditional diet features rice, fish and shellfish, and fruit (especially citrus fruits), but the most unique features are traditional Japanese foods such as miso, seaweed, pickled vegetables, green tea, soybeans, soybean sprouts, and mushrooms (such as shiitake mushrooms). In addition, this diet is also characterized by low intake of red meat and coffee. It is important to note that the traditional Japanese diet is a cultural custom that people are accustomed to following in their daily lives, rather than a diet designed to achieve a specific goal such as weight loss.

Traditional Japanese foods such as miso, seaweed, pickled vegetables, green tea, soybeans, soybean sprouts, and mushrooms may be closely related to the longevity of the Japanese population.

What are the effects of the three dietary patterns of "traditional Japanese diet", "typical Western diet" and "vegetable, fruit and dairy diet" on brain atrophy?

The study observed 1,636 Japanese adults aged 40 to 89, asking participants to record everything they ate over a three-day period to establish their typical diet composition. Participants were also provided with disposable cameras to record their food intake before and after each meal, thereby calculating each person's average daily food intake as a measurement baseline for understanding the participants' normal eating habits.

Then, based on these dietary records, the study divided the participants' eating patterns into three types: "traditional Japanese diet" (589 people), "typical Western diet" characterized by high intake of refined carbohydrates, high-fat foods, soft beverages and alcohol (697 people), and "vegetable, fruit and dairy diet" with higher-than-average intake of plant-based foods (350 people).

To account for diet as the only manipulated variable, the study also collected information on other lifestyle and health factors, including whether the participants had a genetic susceptibility to dementia (such as APOE genotype), whether they smoked, their level of physical activity, and whether they had health problems (such as stroke or diabetes), and adjusted the analysis after taking these factors into account. The study then looked at the participants' brain neuron loss to analyze changes in brain atrophy over the two years.

What explains the gender differences in how dietary patterns affect brain health?

The study found that women who followed a traditional Japanese diet had less brain atrophy during the two-year study period compared to women who followed a Western diet; the effect of a vegetable, fruit and dairy diet was not clear due to insufficient sample size. Why did the traditional Japanese diet only have the effect of slowing brain atrophy in female participants, while different dietary patterns did not produce any difference in the amount of brain atrophy in male participants?

This gendered difference may be attributed to both biological and social reasons: In terms of biological conditions, certain nutrients - such as magnesium and phytoestrogens in fish, shellfish, mushrooms, whole grains and beans - have a stronger protective effect on women's brains. In terms of social factors, differences in the impact of diet on brain health may also be attributed to differences in lifestyle habits between the sexes. Some behaviors that may offset the benefits of a healthy diet, such as smoking, are more common among men than women. In addition, male participants are more likely to deviate from the traditional Japanese diet and tend to consume more refined carbohydrates, such as noodles, and alcoholic beverages, such as sake, than females. Both factors may lead to brain shrinkage.

Japanese men consume more alcohol and refined carbohydrates than women in their eating habits, making them less likely to benefit from the protective effects of the traditional Japanese diet on brain health, the study suggests.

Antioxidant and anti-inflammatory effects of traditional Japanese diet are key to maintaining brain health

Overall, the study points to differences in the impact of dietary composition on brain health between the sexes. While the exact reasons need to be further studied, the benefits of the traditional Japanese diet on the brain are clear: many of the foods are rich in vitamins, polyphenols, phytochemicals, and unsaturated fatty acids, all of which are known for their antioxidant and anti-inflammatory effects, meaning they help keep the brain and its neurons functioning optimally. The traditional Japanese diet, which includes elements such as fish, seafood, soy, miso, seaweed, and shiitake mushrooms, may help improve not only cognitive function but also overall health.

Review Editor: Lin Yuting