Study Reveals Diet's Heavy Role in Cancers

By Christopher Wanjek, LiveScience Bad Medicine Columnist

China is at long last getting a taste of the West: cars, home electronics, meat with every meal, and, sadly, breast cancer.

A study published today in the July issue of Cancer Epidemiology, Biomarkers & Preventions provides more results from the landmark Shanghai Breast Cancer Study, originally conducted in the 1990s by researchers at Vanderbilt University.

The study revealed that women in Shanghai who ate what the researchers called a "Western meat-sweet diet" heavy on meat, starches and sweets, more than doubled their risk of developing a main form of breast cancer, called estrogen-receptor-positive cancer, compared to their neighbors who ate a more traditional vegetable-soy-based diet, according to a team led by doctors at Fox Chase Cancer Center in Philadelphia.

The pattern was particularly evident in overweight postmenopausal women, who likely gained the extra pounds from the meat-sweet diet, according to Dr. Marilyn Tseng of Fox Chance, who led the analysis of several thousand women ages 25 to 64.

Have genes, will travel

The results, however profound, are not unexpected. Numerous studies conducted of immigrant groups in the United States over the past 20 years have been uniform in revealing that the Western diet breeds certain kinds of cancers, specifically colon cancer and hormone-related cancers such as breast, prostate and ovarian. Breast cancer rates are four to seven times higher in the United States than in Asia, according to the National Cancer Institute.

Such studies have found that first-generation immigrants have nearly identical cancer risks compared to those in their native country. But within a few generations of living in the United States, the patterns become identical to those of fellow Americans.

Asia isn't immune to cancer. Asia has high rates of stomach cancer, from highly salted and nitrite-containing foods; liver cancer, from hepatitis B and C infections; and nasopharyngeal cancer, from smoke from old stoves. Immigrants and their descendants reduce their risk of these cancers upon moving to the United States.

This swapping of cancer risks only emphasizes diet and environment and downplays genetics as the major cancer risks. Immigrants pack up their genes with them on their journey but leave their diet and lifestyle back in their homeland.

Genetic contribution

Some people are destined to develop cancer, regardless of diet. Colon cancer is nearly a sure thing, for example, for those with a hereditary disease called Familial Adenomatous Polyposis; they begin to develop cancerous polyps often while in their 20s. This is genetic, and it is very rare.

Scientists are identifying more and more genes associated with cancer, particularly with the advent of genome-wide association studies based on the Human Genome Project and new technologies made available in the past year. Such studies are important to determine the extent of a person's genetic predisposition to a disease as well to create personalized medicines.

As reported in Nature Genetics on July 8, researchers at the Ontario Institute for Cancer have found a section on Chromosome 8 associated with 20 percent increase in colorectal cancer. That's significant, a 1.2-times increase in risk. But compare that to the way diet is behind the twofold increase in breast cancer in Shanghai and the four- to seven-times increase risk of breast cancer for the descendants of Asian immigrants in America.

Genes, researchers often say, are the cards dealt to you in life. Few of us are dealt a perfect hand, but wise choices on diet and lifestyle can help keep you in the game.