In addition, estradiol is carried in the blood on special carrier molecules. On high-fat diets, more estradiol breaks free from its carrier molecules and becomes biologically active, like soldiers jumping off a jeep and starting their attack. So high-fat diets may promote cancer by increasing the amount in addition to promoting the biological activity of estradiol in the body. Another problem with high-fat diets is that the meat, poultry, fish, and dairy products that usually make up such diets are devoid of fiber. Fiber is the part of plant foods that resists digestion in the intestinal tract.
Evidence suggests that fiber helps reduce estrogen levels by trapping it in the digestive tract.
In addition, soybeans, which are a mainstay of Asian diets, contain phytoestrogens, which are very weak estrogens which can compete with and blunt the effect of normal estrogens. In the process, soybean products have been shown to reduce cancer risk. So high-fat diets increase estrogen production, apparently increasing cancer risk. Since meat, poultry, fish, and dairy products contain no fiber at all, they increase the fat content and reduce the fiber content of the diet by displacing plant foods. Since most Americans are on high-fat diets, one might ask if the resultant elevation of estrogen has other effects.