The latest trend in natural foods marketing—combining soy and flaxseed—is so ubiquitous you could dine on the combo at every meal. You could start with a breakfast of Zoe's Flax & Soy Granola with a side of Van's Soy-Flax Waffles, then snazz up your lunch with a handful of Trader Joe's Soy & Flaxseed Tortilla Chips. For an afternoon treat, you could munch on Real Foods' flax and soy Corn Thins and later have a midnight snack of a bowl of Back to Nature Flax & Fiber Crunch (with soy grits).
Of course, both foods are moving just fine on their own—sales of soy foods have increased 44 percent since 2001, and flax has become known as the richest vegetarian source of omega-3 essential fatty acids, prompting even mainstream bakers like Oroweat, U.S. Mills, and Roman Meal to sell flaxseed-enriched breads. So, why the sudden urge to combine these two in so many products?
The answer is that both soy and flaxseed contain phytoestrogens (plant estrogens), which can mimic human estrogen. There has been a lot of talk that this capacity could help relieve menopausal symptoms, like hot flashes.
Since soy and flaxseed are cousins but not identical twins—the phytoestrogens in flaxseed, called lignans, have a significantly different structure from the soy phytoestrogens—they may work differently in the body, says Lilian Thompson, professor of nutritional sciences at the University of Toronto and the queen of flaxseed research. Combining soy and flax in foods like protein bars or waffles may offer two sources of health protection; however, there's no hard evidence yet to suggest that their combined effect is greater than that of each alone.
Of course, just about the time menopausal women were hearing the news, research was showing that slurping down vast quantities of soymilk or soybean chili might actually increase your risk of breast cancer. As so often happens with modern medical dilemmas, newspaper headlines tilted back and forth, one week trumpeting the benefits of taking in ample amounts of phytoestrogens, and the next week decrying the risks.
It's tricky to figure out whether to stock up on soy-and-flax cereal or avoid the aisles brimming with snacks touting the duo. Will the pair tame your hot flashes and restless sleep? Will they lower your breast cancer risk or bump it up?
And soy does not affect hormone levels. In 30 studies, soy didn't raise estrogen levels. Theoretically that's a good thing, since increased estrogen may stimulate tumor growth, increasing the risk of breast cancer. Soy may also increase the length of the menstrual cycle by one day, says Mark Messina, adjunct associate professor of nutrition at Loma Linda University in Loma Linda, California. Which is also a good thing, since longer cycles are associated with decreased risk of breast cancer. And flaxseed may block prostaglandins, hormone-like substances that, when released in excess during menstruation, can cause heavy bleeding.