In the mid-1990s, Japanese girls experienced the biggest change at the primary school 6^th grade level as they were taller than their postwar 1940s counterpart by nearly 16 cm.  As for female 7th graders, they are more than 12 kg heavier than their postwar 1940s counterpart.  Now, Japanese over 5 feet 7 inches or even 6 feet are very common.  (Related:  Leg extension surgery)

                Dietary changes. One of the largest dietary change is probably consumption of milk. Not only has it made Japanese women grow taller, bigger and stronger but the consumption of milk has also advanced the age at which first menstruation happens in Japanese girls from 15 in 1950 to 12 years in 1975.  Only in the US has this record been somewhat matched and surpassed. Girls in the US are reaching puberty,  for example, as early as eight years old according to some reports and puberty is also accelerating though the national average is still about 12. This means that Japanese women have now reached the forefront of first world standards in female puberty. The implications need to be studied more.  

In the same time period of 25 years after WWII, Japanese women have also grown more than 4 inches in height. Their weight increased by nearly 10 kg in the same period. Many scientists attribute this growth to the fact that Japanese consumption of dairy products now amounts to more than 50 kg per year, including cheese, milk, butter etc. Percentage of fat has also gone up with the intake of dairy products and that probably explains why Japanese women are now heavier.

American and Japanese researchers have identified over 50 hormones in milk that could possibly explain this phenomenon. The government and private sector has also played a key role in promoting milk,  making it readily available in offices, schools as well as vending machines in railway station. Hormones work in minute amounts and only a small tablespoon (or micrograms) of female hormones like estrogen or progesterone can produced a monumental effect on women’s growth.

Some researchers argue that there is a genetic potential for each race and that the Japanese are reaching their potential through improved diet but this is controversial and not readily proven. This is a controversial theory as it is not known if this so-called genetic potential may become a limiting factor on female growth in Japan. Would it be a genetic limitation such that Japanese women or indeed Asian women will never grow as large as Western women? Will the science of genetics or life sciences or biotechnology or genetically modified food in the future change this genetic potential? All questions remained unanswered.