Many studies have been carried out on cancer rates among migrant workers. Two studies looked at Japanese migrants who moved to Hawaii and whose next generation moved to California. The incidence of breast cancer was found to be very low in Japan, probably because of dietary factors. When the same hereditary population moved to Hawaii and adopted some American customs, the incidence of breast cancer rose. When the same genetic population then moved to California and adopted the American-style diet, the cancer rate increased to the same level found in native-born Americans.

Diet  Obesity, defined as being 40 percent or more overweight, may increase your risk for several types of cancer. High levels of fats in the diet—both saturated (hard, mostly animal) and unsaturated (liquid, mostly vegetable oil)—appear to play a role in causing cancers of the colon, rectum, prostate, testes, breast, uterus and gall bladder. Even lean people, if they eat high-fat and low-fiber diets, run increased risks of developing these tumors.
    Low fiber consumption may contribute to the rise in colon and rectal cancers. Grains have always been one of humanity's basic foods. In days past, we would eat grains, and foods made from them, in their simplest form—whole and unrefined. Paleolithic people ate five to ten times more fiber than we do now. About 150 years ago, a new milling process tempted our tastebuds with refined white flour. But when the husk was removed from the grain, so was the fiber. Fiber has the power to dilute cancer-causing toxins, such as dietary fat, and move them through the bowel quickly so they have less time to cause harm. Some studies suggest that people who eat a high-fiber diet may reduce their risk for colon cancer by up to 40 percent.