Soy protein has already been shown to have a protective effect on hormone-related cancers including breast cancer and prostate cancer. But if the link between estrogen and colon cancer is confirmed, the study could further expand the benefits of the natural phytoestrogen.
Cancer of the colon or rectum is the second deadliest form of cancer after lung cancer but is also considered one of the most preventable types of cancer, as there are several dietary factors that appear to play a protective role against the disease.
"This study suggests that colon cancer may be a hormone-responsive cancer which may provide new ways to treat and or prevent this disease," said Ruth MacDonald, professor of food science at the University of Missouri-Columbia in the US. "In addition, we discovered that soy protein could have a very positive effect on the number and size of tumors that do occur."
For the study, published in the January issue of the Journal of Nutrition (134:179-182), MacDonald fed female mice five different diets, and then followed their progress for a year. The five diets were designed to compare the effects of specific ingredients.
Diet one was made with milk protein, and diet two contained soy protein. Both diets were lacking any kind of estrogen. The other three diets contained soy protein with the addition of an estrogen component. Diet three contained soy protein and genistein, an estrogen-like compound found in soy. Diet four contained ADM's Novasoy, containing a mixture of soy-derived compounds including genistein, and diet five contained estrone, a naturally occurring human estrogen.
MacDonald found that while all the soy/estrogen diets gave some protection, the diet containing estrone was the most effective in preventing colon cancer. This is the first time such a finding has been documented. The dose of estrone the mice received was similar to levels used in hormone replacement therapy.
The researcher also discovered that those mice that ate soy protein and did develop colon cancer had fewer and smaller tumors than those mice that did not eat soy protein.
"We know that soy protein may be helpful in the prevention of heart disease, but this work suggests it may also be beneficial in the prevention and control of colon cancer. The good news is that there are many ways to add soy to your diet now and we know of no harmful side-effects to eating soy protein," said MacDonald.
MacDonald is continuing her study to determine how the compounds work to provide protection of colon cancer.