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Where do we stand on soy?

3/9/2017, 1:28 a.m.
Tofu or snafu? Soy has become a big component of a plant-based diet, but debates have raged for decades over ...
Chicken with curry paste and french green beans. (Photo: Metro Creative)

— "If you put China, Japan and Korea and southeast Asia together, you have more than 2 billion people, and these people consume 20 to 30 times more soy than the average American every single day of their lives," he said. "It's part of their diet, and this has been going not just for hundreds of years. It has been going on for thousands of years."

With a long history in Asia, soy slowly emerged as a common food source in the US in the 1960s. During this time, states formed soybean industry groups affiliated with the American Soybean Association, which was funding research to find uses for soybeans and ways to reduce production costs.

1970s: The rise of soy in the American diet

By the early 1970s, more studies shed light on the use of soy proteins in baked foods and the functional properties of soy proteins.

The American Soybean Association established its headquarters in St. Louis in 1978.

Around that time and later, contradicting studies about the potential health benefits of soy arose, creating confusion.

1980s: Setting the record straight in animal, human studies

Two animal studies -- one on monkeys published in 1986 and another on rats published in 1987 -- suggested that soy diets caused an enlarged pancreas and were associated with the growth of pancreatic cancer in those animals.

In response to those studies and others, the National Cancer Institute's Division of Cancer Etiology organized a workshop to discuss the state of research on soy in relation to cancer risk.

After the workshop, participants published a report in the journal Cancer Research in 1989 (PDF). They wrote that there was no evidence that soybean-derived foods had adverse effects on the human pancreas.

Rather, it was observed that human populations with high levels of soy in the diet had decreased rates of pancreatic cancer.

In the years to come, cancer researchers would tout the potential cancer prevention benefits of soy foods.

1990s: The breast cancer, soy connection explained

Among the first of many studies to suggest that soybeans contain potentially anti-carcinogenic benefits, providing something of a protective effect against cancer, was a 1991 study published in the Journal of the American Dietetic Association.

Things changed in 1996. That was the year a pilot study, published in the journal Cancer Epidemiology, Biomarkers, & Prevention, suggested that consuming soy protein might actually stimulate the growth of breast cancer cells.

This confusion about whether soy is good or bad for cancer risk stems from the fact that soy isoflavones can mimic estrogen in the body and can bind to estrogen receptors, said Kucuk, the medical oncologist.

"Some people naively thought, 'Well, since they're estrogenic, they must be bad, because estrogen causes breast cancer.' We all know that in women, estrogen levels are associated with a higher risk of breast cancer. So they're immediately jumping to the conclusion that, well, if estrogen causes breast cancer in women, since soy has plant estrogen, it must cause breast cancer," he said.

"There are two estrogen receptors (in the human body): alpha and beta. Alpha is the bad one. That's the one where, if something binds to alpha, it may increase the risk of breast cancer, because it makes breast cells grow. But beta, on the other hand, it causes the opposite effect," he said. "Soy isoflavones bind preferentially to estrogen receptor beta."