Traditional Japanese diet components may improve mental health: Population study
Rice consumption may have a positive impact on mental health, with other foods central to the traditional Japanese diet acting as mediators, according to researchers in Japan.
FAB RESEARCH COMMENT:
This study was purely observational - so for that reason alone, the findings cannot be used to make any inferences about causality without (1) additional evidence, and (2) sound theoretical backing - i.e. involving established scienttic evidence of basic mechanisms.There are many possible reasons why individuals consuming a more traditional Japanese diet might score better on measures of mental health (and general health, as the two go together), quite apart from their consumption of more rice.
Inspection of the full article (which is open access) shows that statistical analyses were carried out to examine possible 'mediating' effects of some other dietary correlates of rice consumption - but no explanation is given for why one of those correlates (consumption of 'low-fat fish' was then ignored in the model presented!)
Correlational studies like this in the field of nutrition and diet are also open to numerous confounds that can never be fully accounted for, owing to
- the difficulties of assessing dietary intakes accurately (even current, let alone retrospective reports are known to be unreliable)
- the strong links between eating habits and numerous other variables - e.g. in this study, older age was (unsurprisingly) very strongly associated with reported consumption of a more traditional Japanese diet. And while age itself can be statistically controlled for, many other factors related to eating habits would go unmeasured, and therefore uncontrolled.
- difficulties of inferring nutrient intake or status from dietary report alone (nutrient intakes can only ever be rough approximations, owing to inaccuracies in initial reporting, and the limitations of databases linking foods or food groups with their supposed nutritional content)
Read the underlying research:
While the traditional Japanese diet (or Washoku) is generally said to be nutritious and balanced, its actual benefits - particularly with regards to mental health — have not been properly detailed.
In order to ascertain the health benefits of Washoku, researchers from Hokkaido University and Tenshi College conducted a survey to assess the dietary habits and mental and physical health of the Japanese population.
In order to ascertain the health benefits of Washoku, researchers from Hokkaido University and Tenshi College conducted a survey to assess the dietary habits and mental and physical health of the Japanese population.
They recruited 278 physically and mentally healthy participants and assessed their daily intake of staple foods such as rice, rice-based foods, bread, noodles, cereal for their three main meals (breakfast, lunch and dinner).
Have you bean eating your rice?
Subsequently, they observed "associations between rice consumption and improvements in quality of life (vitality) and sleep quality", whereas bread and noodle consumption did not have the same associations.
They said this was consistent with previous research, and added that consuming a combination of rice and another Japanese dietary staple, miso (soybean paste) soup, could also have a positive impact on both physical and mental health.
They said this was consistent with previous research, and added that consuming a combination of rice and another Japanese dietary staple, miso (soybean paste) soup, could also have a positive impact on both physical and mental health.
They referred to a recent longitudinal study that had assessed changes in the Japanese diet every 15 years — from 1960 to 2005 — and found that the 1975 Japanese diet, which contained more rice and miso soup, contributed the most to preventing cognitive decline. This was attributed to the flavonoids in miso, which are believed to help promote brain function and learning ability, as well as enhance memory. They are also said to aid in preventing cancer, heart disease and osteoporosis.
In addition, the researchers wrote that "a rice-centred diet may have negative effects on impulsiveness".
Other factors and mediators
They noted that how long an individual has been regularly consuming Washoku might also affect its impact on one's health.
The present study's subjects were all at least 40 years old, meaning they had been consuming the recommended traditional diet since 1975. As such, "the foods identified as associated with improvements in health might correspond to representative foods in the participants' diets throughout their lifespan".
The present study's subjects were all at least 40 years old, meaning they had been consuming the recommended traditional diet since 1975. As such, "the foods identified as associated with improvements in health might correspond to representative foods in the participants' diets throughout their lifespan".
The study also made mention of other health mediators central to Washoku, namely, green tea and natto (fermented soybean), which have been major components of the diet since 1975. The researchers concluded:
"The present study suggests an association between rice intake and physical and mental health, with indirect contributions from intakes of other foods as mediators. The foods that were associated with improvements in health were components of the traditional Japanese diet.
"The present study suggests an association between rice intake and physical and mental health, with indirect contributions from intakes of other foods as mediators. The foods that were associated with improvements in health were components of the traditional Japanese diet.
"The contribution of the rice-centred Japanese diet to health may be explained by the effects of mediators, which are foods that have been familiar to the Japanese for a long time. Further research is required to assess the associations between modern foods and health and the biological mechanisms underlying these associations."
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