Increased Incidence of Inflammatory Bowel Disease in Association with Dietary Transition (Westernization) in Japan.

Introduction: Inflammatory bowel disease has become a global disease, but its key environmental factors still remain unrecognized. This study aimed to clarify the role of dietary transition (westernization) in the increased incidence of inflammatory bowel disease in Japan.

Methods: Annual numbers of new cases of inflammatory bowel disease in Japan over the period from 1965 to 2000 found in a nationwide database compiled by the government and the daily amount of food and nutrient intake per capita for the same period revealed by the National Nutrition Survey have been used to analyze their interrelation.

Results: Rapid increases in the estimated incidence per 100,000 population have been observed, that is, from 0.08 in 1965 to 4.8 in 2000 for ulcerative colitis and from 0.003 to 1.3 in 2000 for Crohn's disease, with an extremely high correlation between the annual numbers of new cases of the respective diseases (r = 0.970). Intake of both animal fat and animal protein increased, while intake of rice decreased during the period. Of all food groups, the intake of rice as a staple food showed the highest negative correlation coefficient with the numbers of new cases of both ulcerative colitis (r = -0.825, 95% CI: -0.908 to -0.681, < 0.0001) and Crohn's disease (r = -0.836, 95% CI: -0.914 to -0.700, < 0.0001).

Conclusions: An increased incidence of inflammatory bowel disease was observed to coincide with dietary westernization in Japan. Our results support the assertion that dietary westernization is a key environmental factor in inflammatory bowel disease.