Migrant studies of people who migrated from one area to another and started eating the typical diet of their new area assumed the disease risk of that new area to which they moved. These studies strongly implied that diet and lifestyle are principle causes of the diseases and that genes are not necessarily that important. In a summary of many of these studies that was presented to the U.S. Congress, Sir Richard Doll and Sir Richard Peto, both of the University of Oxford, concluded that only 2-3% of all cancers could be attributed to genes.
Touching and expanding upon what was discussed in yesterday’s post, higher dietary fat is associated with higher blood cholesterol, which along with earlier age of first period (menarche) and higher female hormone levels, are associated with more breast cancer. The average age of menarche in rural China is 17 years, compared to the average age in the U.S. of roughly 11 years. The strong association of a high-animal protein, high fat diet with reproductive hormones and early age of menarche raise the risk of breast cancer. Furthermore, consumption of a diet rich in animal-based food causes hormone levels to remain high throughout the reproductive years, deferring menopause by three to four years and extending the reproductive life by a total of about nine to ten years, thus increasing the lifetime exposure to female hormones. Other studies have shown that an increase in years of reproductive life is associated with increased breast cancer risk.
Multiple observations, tightly networked into a web, show that animal-based foods are strongly linked to breast cancer. Individual parts of this web were consistently correlated and in most cases statistically significant, and this effect occurred at unusually low intakes of animal-based foods.
- Campbell, T.C., and Campbell, T.M. The China Study, Dallas, BenBella Books, Inc., 2006, p. 84-89.