Breast cancer was exceedingly rare. But over the years, as Western influences have altered Japanese eating habits, breast cancer rates have climbed dramatically. These international studies are just one line of evidence, however. Such studies have also shown a link between fatty diets and higher risk of breast cancer, and even on cancer patient's chances for survival. One study tracking Canadian breast cancer patients for ten years found that for every 5 percent increase in saturated fat in diets, the risk of dying of breast cancer shot up by 50 percent.
Fats increase the amount of estrogen in the blood.
In turn, this hormone stimulates breast cells in such a way that cancer is more likely to occur and is more aggressive. Fatty foods also lead to obesity which itself is linked to higher estrogen levels in the blood. Despite such evidence, doubts about the fat connection have persisted, fueled mainly by the results of a large study of nurses run by Harvard University in which researchers found no association between fatty diets and breast cancer rates. Unlike the populations examined in international studies, the nurses were a fairly homogeneous group, all eating fairly high-fat diets. No group in the study was following anything similar to a traditional Asian diet or other low-fat diet.