Changes in dietary fiber intake among Japanese in the 20th century: a relationship to the prevalence of diverticular disease

In view of the fact that Japanese dietary patterns have been undergoing rapid “Westernization,” in part characterized by decrease in fiber, we assessed dietary and crude fiber content in the Japanese diet using food consumption tables for the period from 1911 to 1980, and studied the trend in the reported prevalence of diverticular disease of the colon. Fiber content declined in diphasic pattern: the first decline, which probably had started in the late 19th century, progressed until the Second World War. Although records during the war period were unavailable, the high fiber content of the Japanese diet in the period immediately after the war reflects the tendency to supplement rice with more fiber-rich cereals, and to increase the amount of rice through reduced polishing during the war time. The second decline in fiber content in the Japanese diet, which started in the 1950s and progressed throughout the period of “high economic growth,” was mainly due to the decrease in cereal consumption. The changes in crude fiber content in the Japanese diet after the Second World War resemble the pattern of rapid decline noted in the United States during the 1930s to the 1950s. The prevalence of diverticular disease in both countries also shows sudden steep upward turns during the period between 1930 and 1950 in the United States and the late 1970s in Japan, suggesting the presence of threshold level(s) of fiber intake for the effective prevention of diverticular disease. The prevalence of diverticular disease is still relatively low in Japan. However, if the current dietary trend continues, it may rise to a level currently found in the “Western” countries in the coming few decades.