I answered a similar question recently, here.

In sum: the Japanese population has been growing taller every generation since the late 19th century, and there was a particular jump in size after World War II, when amount of protein in the diet and total number of calories consumed per capita noticeably increased in Japan. A diet very low in protein pre-war resulted in people being shorter, especially in the legs, but also all over the body. During World War II, the average height of Japanese soldiers was 5 ft. 3-1/2 inches and 120 pounds, while the average height of an American soldier in WWII was 5 ft. 7 inches and 140-150 lbs.