The health perspective on soy has been a much debated topic over the past several years. Proponents of soy consumption have pointed out that it’s contains high levels of fiber, protein, calcium and iron, all of which could use a boost for many in the U.S. But detractors have indicated that certain chemicals contained in soy are similar in structure and function to the hormone estrogen and have raised concern about the possible effects these compounds might have on the human body. New research out this week helps push debate in the direction of the health benefits of soy by indicating that it may help prevent, rather than stimulate, cancer growth.
What is a phytoestrogen?
The conversation around the health effects of soy have centered on a group of chemicals called “phytoestrogens” that are found naturally in soy. As the name suggests, phytoestrogens are estrogen-like compounds that are found in plants. Estrogen is a key hormone in the human body and is especially important for sexual development and regulation in women, although men also need and use low levels of estrogen.
Because these phytoestrogens are very similar in structure to human estrogen, there has been some concern that they could bind to the same receptors in the body that estrogen binds to and activate those receptors in ways that might not be good for health. In particular, there have been concerns about cancer. That’s because some cancers, like breast cancer, use high levels of estrogen to grow and develop more rapidly. Some have also raised concerns about possible effects on male fertility, but no studies have shown this to be of real concern.
What is known about soy and breast cancer?
Several studies have tried to get a sense of whether phytoestrogens actually pose a cancer risk. This has been done in two ways. On a cellular level, researchers have applied the most common phytoestrogen in soy to breast cancer cells and have found that they can boost the growth of those cells. But studies looking at regions of the world that eat lots of soy compared to regions that don’t have found the opposite effect, namely, that those who eat more soy tend to have lower rates of breast cancer. These confusing and apparently contradicting effects were what led this research team to try and get a better sense of what was really going on.
How did the researchers test the effects of soy?
The researchers took a group of mice and removed their ovaries to better model how women after menopause might respond to the effects of soy. They fed some mice a pure form of phytoestrogen from soy, called genistein, and another group of mice a diet with soy flour. They also had a group of mice that received hormone replacement and another that received nothing but a placebo pill. They injected all of these mice with breast cancer cells that would cause tumors if left unchecked. After 12 weeks, they euthanized the mice and looked to see what had happened to the cancer cells.
They found that mice that ate soy flour had smaller tumors than those who had received the placebo, indicating that the soy flour had helped to combat the growth of the cancer cells. The mice that had the pure phytoestrogen, though, had larger tumor growth, indicating the purified chemical had enhanced the cells ability to grow. The researchers examined the genetics of the tumors in all sets of mice. They found that soy flour helped boost the use of genes that help prevent cancer, while the pure genistein helped to turn on genes that revved up cancer.
How do the researchers explain this effect?
The researchers think their results show that more is going on in soy that we truly understand. While their findings with genistein support past findings that phytoestrogens can help cancer growth, the study overall shows that soy’s effect on the body is much more complex. There are probably a variety of components present in the plant material as a whole that work together to fight cancer. In essence, the effects of soy are greater than just the sum of its parts.
How does this affect me?
Some people have avoided soy out of fear that it might cause breast cancer. This study shows that to be unlikely. Soy products, as most people eat them, are probably safe and may even help prevent breast cancer in the long run as other studies of human populations have shown. The researchers say that those with breast cancer or a history of breast cancer should probably avoid any supplements that contain purified plant estrogens, since their data shows that these purified forms may encourage tumor growth.