The benefits of the Japanese diet of drinking green tea and eating raw fish are extolled in a new study by Craig Wilcox, a leading gerontologist. This study tries to link the fact that Japanese women live longer than any others with their “ultra-healthy diet”. They live to an average of 86.4 years, 3.7 years older than British women at 82.7 years and even the famously healthy Italians at 84.4. But Japanese men do not fare so well, with average life expectancy of 79.9 years, coming behind Iceland, Sweden and Switzerland in the international league table.
Again a substantial amount of money has been spent on a scientific study trying to show that our longevity is totally shaped by our environment. Again it has not corrected for genetics, so no conclusions can be drawn regarding the healthiness or otherwise of Japanese food.
I had the great pleasure of living in Japan for three years and experienced their excellent food first hand. Their diet is considered healthy for a number of reasons, but mainly because it is very low in sugar, particularly fructose, compared to a Western diet. Their main carbohydrate is white rice, which is usually eaten at the end of a meal as a filler, so in smaller amounts. They do not eat desserts, as we would understand them. They also eat a lot of low glycaemic index foods such as raw fish and vegetables. Their portions are certainly smaller, but then so is the average Japanese body size. In any case, the many courses consumed over the prolific number of business dinners I attended added up to a lot of calories, particularly when considering the copious amounts of beer and nihon-shu (Sake) we were forced to consume.
The point that is usually missed amongst all this enthusiasm for their diet is that the Japanese are genetically distinct in many ways. Before a pharmaceutical product can be registered for sale in Japan their regulatory authorities insist that separate clinical studies to be conducted on ethnic Japanese patients. This is because there are many instances where Japanese react very differently to drugs compared to their Western counterparts – demonstrating different genetics and different metabolic pathways.
Compared to Westerners the Japanese have naturally lower levels of body fat but higher blood cholesterol levels for comparable fat intake. They have higher mortality from stroke but lower mortality from coronary heart disease. The Japanese have unique versions of ethanol-metabolizing enzyme genes compared to Westerners, which affects their response to alcoholic drinks. They have lower rates of lung cancer despite higher smoking rates then the West, however they are more susceptible to stomach cancer (4 times UK levels).
The different genes in our pet cats compared to ourselves has an enormous effect on our expected longevity. The 3.7-year difference in life expectancy between Western and Japanese women could be entirely genetic.
How much of these differences are due to genes and how much is due to diet is difficult to assess. This study has not shed any light on either. I shall continue to eat Japanese food for its organoleptic qualities and reserve judgment on its health effects.