Through the westernization of the eating habits of Japanese people after the Second World War, their kinds of diseases were westernized, too. Intake of animal protein and its percentage in total protein intake have been increasing. Along with that, age-adjusted mortality rates of colon, pancreas, and breast cancers have been increasing. By contrast, that of gastric cancer has been decreasing. Standard mortality ratios of colon, pancreas and breast cancers are high and that of gastric cancer is low in Hokkaido Prefecture where the lifestyle of the inhabitants is more westernized than in the other parts of Japan. The results of case-control studies performed in Hokkaido Prefecture coincide with these facts; intake of western foods accelerates the occurrence of colon and pancreas cancer, and intake of traditional Japanese foods suppresses it. With regard to gastric cancer, however, these foods work totally to the contrary.