Aug. 30, 2001 -- Move over, soy, flaxseed might be another natural way of preventing breast cancer. Postmenopausal women who ate ground flaxseed had reduced levels of the sex hormones associated with breast cancer.
Recently, soy has been the subject of medical research because it is high in phytoestrogens. When people eat products that contain phytoestrogens, these plant-based substances behave like a very weak version of the female sex hormone estrogen. In cultures where a lot of soy is eaten, such as in some parts of Asia, rates of breast cancer are quite low.
To date, medical studies suggest that a soy-rich diet might help North American women reduce their risk of breast cancer, although the research is far from clear. There is also some evidence that too much soy might actually increase your risk of breast cancer.
It turns out that the seeds of a pretty little blue flower called flax are a great source of phytoestrogens, too. As a result, Joanne Slavin, PhD, RD, professor of nutrition at the University of Minnesota at St. Paul, decided to see how flaxseeds fared in the ongoing battle against breast cancer.
"There hasn't been a lot of study on flax relative to soy," she tells WebMD. "Since flax is another concentrated source of phytoestrogens, ... maybe we should think of flax. It also alters estrogen and [other] sex hormones in a way that might be protective against breast cancer."
Slavin and her colleagues gave either no flax, 5 grams of flaxseed, or 10 grams of flaxseed every day for seven weeks to 28 nuns in a convent in Minnesota. All the women were aged 65 years or older. The researchers tested the women's blood for levels of sex hormones and also checked their urine for the breakdown products of estrogen.
In the women who ate flaxseed, the concentrations of sex hormones known to be associated with breast cancer were reduced. While this is not concrete evidence that women who eat flaxseed are less likely to develop breast cancer, it does point in that direction. Slavin presented this research recently at the annual meeting of the American Chemical Society, held in Chicago.
"This is supportive of the hypothesis [that eating flaxseed can reduce breast cancer risk]," says expert Lilian Thompson, PhD, who reviewed the research for WebMD. "However, in terms of whether we are able to prevent cancer [with flaxseed], we still don't have data from long-term studies."
However, she adds, research has shown that eating more food high in the type of phytoestrogens found in flaxseed, called lignans, can lower a woman's chances of developing breast cancer. Flaxseed is the richest source of lignans, says Thompson, a professor of nutrition sciences at the University of Toronto in Ontario.
It is important to point out that whole ground flax, which is what the nun's ate, contains more than phytoestrogens. It also contains fibers and omega-3 fatty acids, both of which are known for their health benefits. So it's not 100% certain that the findings are due to the phytoestrogens alone.
Slavin says that flaxseed, which is available in many forms in health food stores, including whole or ground seeds, baked into breads and cereals, or in the form of flaxseed oil, is probably safe to eat, even in fairly large quantities.
"If you use it as a food or even as a supplement in the quantities most people are going to consume," she says, "there may be some benefits, and I don't see a lot of downsides."