Some in the West wondered how Japanese women who are constrained to small spaces in Japan can grow big and tall suddenly. Wealth has also overcome Japanese space constraints as more and more Japanese women go to ultra-modern gyms and sports clubs to train their muscles. Taut, veined athletic muscles are no longer frowned upon in the Japanese fashion world thanks to fitness trends in the US, a source of Japanese emulation.

There are other more minor theories like Japanese moves from sitting on the floor to sitting on chairs, have improved their postures and musculatures accounting for the height and weight increase. Removal of infectious diseases, wealth and better quality of living as well as Japanese infatuation with disinfectant may also be promoting Japanese growth, size and longevity. Other less scientific assertions include more sleep for Japanese improving their metabolism rates. Others have attributed the growth to the many calorie-, vitamins- and minerals-enhanced food and drinks available from vending machines which youngsters drink on their way to night prep schools in place of dinner due to time constraints. 

Besides diet, some Japanese researchers and scientists say increase may also be due to Japanese industrial economy producing large amounts of chemical byproducts that are artificially increasing the sizes of women. Dioxins and polystyrenes have been identified by some as chemical substances that may enlarge and extend Japanese female body sizes. They are hormone effectors that have been found in Japanese soil, river and seas. These substances in Japan have been blamed for low sperm counts and making men develop feminine characteristics. Synthetic estrogens have already caused changes in fish and frogs in the rivers.

Finally, some of these changes in Japanese female physique may also be due to Japan’s state intervention. Some schools for example have their kids or encourage their kids to taking vitamins pills in specially prescribed boxes during lunchtime or have arranged volumes of milk or dairy products to promote growth. Others have prescribed rest time to manage youngsters’ metabolic rates. Schools strictly monitor young children’s diet (Weight loss surgery for children) with regular school inspections of what mothers put in their bento or lunch boxes. They regularly prescribe diets with calorie intakes provided for the parents. Parents also have been educated more through the media and during parent-teacher meetings diets are often discussed to standardize growth promoter diet for Japanese children. (Related article:  Slim Japanese women)

Psychological Factors. Psychologically, Japanese who are afraid that they will stick out because of their height or find it difficult to marry no longer feel like that. Tall women are increasingly envied. In fact, they are so admired that at one time, many Japanese women wear high heel or platform shoes to make themselves look taller, even to the extent of towering over their boyfriends who now have to live with such fashion. 

Another psychological factor studied by some social science and psychology researchers in Japan is the growing assertiveness of Japanese women. They are becoming more aggressive and independent compared to their traditional demure image. It is not known if this is due to biological factors. But women are seen as stronger in careers and personalities. Could chemical compounds be responsible for this change?