Including soy in diet from teenage years could offer best chance of protection
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HONOLULU, Dec. 17 - A study of 120 Asian women conducted by scientists at the Cancer Research Center of Hawaii and Vanderbilt University in Nashville, Tenn., offers more evidence that a long-term diet rich in soy can be linked to a reduced risk of breast cancer - as much as a 50 percent in some cases - according to research presented here today during the 2000 International Chemical Congress of Pacific Basin Societies.
The weeklong scientific meeting, held once every five years, is hosted by the American Chemical Society, in conjunction with its counterparts in Australia, Canada, Japan and New Zealand.
The researchers measured isoflavone levels in the urine of women from Shanghai, China, to determine how much soy they consumed. Isoflavones are water-soluble compounds that are particularly abundant in soy, but only occur in trace amounts in other plants. This makes them excellent biomarkers for measuring soy consumption.
Women with the highest isoflavone levels "experienced a 50 percent decrease in risk to develop breast cancer" compared to those with the lowest levels, according to Adrian Franke, Ph.D., a professor at the Cancer Research Center. Franke and Wei Zheng, M.D., Ph.D., a professor at Vanderbilt's Medical Center, were the lead researchers for the study.
The study appears to underscore the need for women to include soy in their diet consistently, beginning as early as their teenage years.
Based on the pilot data, Franke feels that a diet that includes routine and long-term use of soy is key to reducing the risk of cancer. Asked if middle-aged people could reduce their chances of getting cancer by adding soy to their diet, he said, "It might, but it's a life-long process." He noted that some animal studies indicate that people need to start including soy in their diet from about the time of puberty in order to gain the cancer risk-reduction benefit.
The amount of isoflavones present in the urine of the women in the study correlated well with the amount of soy products they had consumed, Franke noted.
"These findings support a potential breast cancer preventive effect achieved by soy consumption in populations that eat soy food habitually," Franke said. The research also supports other epidemiological evidence for the protective effects of soy, he added.
Dietary questionnaires are the typical method of gathering information about how diet affects health and disease, according to Franke. "We wanted to improve this situation by measuring biomarkers that give better information about potential biological effect and health benefits of specific phytochemicals (molecules in plants) and food groups," he said
Franke is quick to point out that factors beyond diet also play an important role in a woman's susceptibility to breast cancer.
"Japanese living in Japan, for example, are at an extremely low risk of developing breast cancer," says Franke. If they migrate to the United States, he adds, their risk still remains low. But, he points out, "the second generation [the children of those migrating] has an increased risk for developing breast cancer, and is at the same risk as Caucasian women. The third generation [the grandchildren] is at an elevated risk, compared to Caucasians."
Franke says no one knows why this occurs, but says it indicates no genetic factor is involved. "It's the environment that changes, and one big factor in the environment is the diet," he noted. "Of course, there are other influences, such as work and psychosocial-related issues."
Last month, the American Heart Association recommended adding soy protein to daily diets as a way to help reduce high cholesterol levels.
The versatile soybean is used in a wide range of foods and beverages, including tofu, miso, soymilk, soy coffee, butter, veggie burgers, crackers, cookies and flour. The bean's oil also has multiple nonfood uses in products such as caulking compounds, crayons, electrical insulation, hydraulic fluids and paints.
The United States leads the world in soybean production, accounting for about 46 percent of the world's supply. It is a major cash crop for U.S. farmers with a value last year of $12.3 billion, according to the U.S. Department of Agriculture.
More than 8,000 research papers will be presented during this year's International Chemical Congress, which is sponsored jointly by the American Chemical Society, the Chemical Society of Japan, the Canadian Society of Chemistry, the Royal Australian Chemical Institute and the New Zealand Institute of Chemistry.
The paper on this research, AGRO 195, will be presented at 9:35 a.m., Sunday, Dec. 17, at the Hilton Hawaiian Village, Iolani Suite III/IV, 2nd floor, Tapa Conference Center, during the symposium, "Food and Beverage Antioxidants in Health and Disease."
Adrian Franke (pronounced Frank-ee) is a professor in the Cancer Research Center in Honolulu, Hawaii.
Wei Zheng is a professor at Vanderbilt University Medical Center in Nashville, Tenn.