Cognitive decline and dementia now affect more than 55 million people worldwide. This number is expected to increase significantly in the coming decades as the world's population ages.
There are some risk factors for cognitive decline and dementia that we can't change – such as having a genetic predisposition to these conditions. But other habits may be more within our control, as research has shown that some modifiable lifestyle habits, such as smoking, obesity, and lack of exercise, are all linked to an increased risk of dementia.
The role of nutrition in preventing cognitive decline and dementia has also been a focus of scientific research for a long time. For example, many studies have examined the benefits of the Mediterranean diet. This diet appears to have a positive effect on important measures of a healthy brain, such as total brain volume, cortical thickness, and white matter integrity.
our A recent study now suggests following a traditional Japanese diet It may also be beneficial for brain health, and is better than the typical Western diet.
Traditional Japanese diet
Japan is famous for the longevity of its people. For example, Okinawa Prefecture in southern Japan is home to an unusually large number of centenarians. For this reason, Okinawa is known as the Blue Zone, an area where people live exceptionally long lives. The longevity of those living in this region is often attributed in part to their traditional diet.
The typical Japanese diet features foods such as rice, fish, seafood, and fruits (especially citrus fruits). But what makes this diet unique are traditional Japanese foods, such as miso (fermented soybean paste), seaweed, preserves, green tea, soybeans, soybean sprouts, and mushrooms (such as shiitake). It is worth noting that this diet is also characterized by a low consumption of red meat and coffee.
It is worth noting that the traditional Japanese diet is a cultural custom and not a diet designed to achieve a specific goal (such as weight loss). It is simply what many Japanese people regularly enjoy at the dinner table.
Brain health
To conduct our study, we analyzed a sample of 1,636 Japanese adults aged 40 to 89 years. First, we determined participants' typical diet by asking them to record everything they ate and drank over a three-day period. They were also given a disposable camera to take pictures of their plates before and after each meal and produce a visual record of the amount they ate.
By combining the written dietary log and photographs, we then calculated each person's average daily food intake. This gave us a good baseline measure of participants' normal eating habits.
Based on dietary records, we found that 589 participants followed a traditional Japanese diet. Another 697 followed a typical Western diet, characterized by the consumption of large amounts of refined carbohydrates, high-fat foods, soft drinks and alcohol. Finally, a smaller number of participants (350 people) consumed a diet containing an above-average amount of plant foods (grains, vegetables, fruits) and dairy products. We call this way of eating a vegetable, fruit, and dairy diet.
We also collected information about lifestyle and other health factors, including whether the participant had a genetic predisposition to dementia (such as the APOE genotype), whether they smoked, their level of physical activity, and whether they had any existing health conditions (such as stroke stroke or diabetes). We did this to adjust our analyzes to take these factors into account, ensuring that our findings could only be attributed to diet.
We then studied the progression of brain atrophy or shrinkage (neuron loss) over a two-year period. Importantly, age-related brain atrophy is a common marker of cognitive decline and dementia. Brain atrophy was measured using magnetic resonance imaging (MRI).
We found that women who followed the traditional Japanese diet had less brain shrinkage over the two-year study period than women who followed the Western diet. It is unclear what effect a plant-based, fruit-and-dairy diet had, likely due to the small number of participants following this diet.
Interestingly, this effect was only evident in women. There was no difference in the amount of brain shrinkage in the men who followed the traditional Japanese diet compared to those who followed other diets.
There may be several reasons for this pattern of results. Some of them appear to be specific to biological differences between the sexes. For example, certain nutrients — such as magnesium and phytoestrogens found in fish, seafood, mushrooms, whole grains and legumes — appear to have a stronger protective effect on women's brains.
This effect can also be explained by differences in lifestyle habits between the sexes. Negative factors such as smoking, which can negate the benefits of a healthy diet, are found more frequently among men. In addition, male participants were more likely to stray from the traditional Japanese diet, and tended to consume more noodles (a source of refined carbohydrates) and alcoholic beverages (sake) than women. Each of these factors can contribute to brain shrinkage.
The benefits of the Japanese diet may also stem from the fact that many foods are rich in vitamins, polyphenols, phytochemicals, and unsaturated fatty acids. All of these ingredients are known for their antioxidant and anti-inflammatory effects, which means they help keep the brain and its neurons functioning at their best.
It will now be important to conduct further research, not only to confirm our findings, but also to explore some of the reasons for the observed differences between men and women when it comes to their preferred diet and brain health.
Adopting elements of the traditional Japanese diet, including foods such as fish, seafood, soybeans, miso, seaweed, and shiitake mushrooms, helps improve not only cognitive function but also overall health.
*Giovanni Sala is Professor of Psychology at the University of Liverpool, United Kingdom. Xu Zhang is a research associate in nutritional epidemiology at the National Center for Geriatrics and Gerontology in Japan.
This article was originally published in English on The Conversation.
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