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Anyone who's been keeping tabs on health headlines lately is bound to be baffled: One week, popping a multivitamin is good and eating soy is bad; the next week, it's the reverse. . .whaa?

The fact is, contradictory research is the norm in the science world. But when new findings refute an established, firmly held belief--as many have recently--it can be especially confusing. But don't fret: WH has uncovered the real scoop behind several current head-scratchers.

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Old thought: Flossing may help your ticker.

For decades, doctors touted the link between periodontal disease and heart disease. They thought the bacteria that collects between the teeth and causes gum disease could also enter the bloodstream, where it could trigger an inflammatory response in blood vessels and increase your risk for heart disease and stroke.

New thinking: What happens in your mouth stays in your mouth.

There's no solid evidence to support the idea that poor oral hygiene causes heart disease or stroke, an American Heart Association committee concluded after reviewing 500 journal articles and studies. The report, published in Circulation, points out that factors such as smoking and diabetes can contribute to both gum and heart diseases. But that doesn't mean one condition causes the other.

Your move: Floss on!

Just not for your heart's sake. Flossing reduces your risk for gum disease (which can be painful and lead to tooth loss) and prevents foul breath, so you should still do the deed once a day, says Sally Cram, D.D.S., a Washington, D.C., periodontist.

Old thought: Soy is a no-no if you (or a family member) have had breast cancer.

Because soy contains isoflavones, plant compounds that mimic estrogen, doctors had long been concerned that eating tofu and edamame could promote cancer development since many breast tumors are fueled by estrogen. Research has even suggested a direct link; a 2006 study found genistein, a component in soybeans, stimulated the growth of breast tumors in mice.

New thinking: Soy foods can be safe for all women.

And not only safe but also protective: A 2012 study of almost 10,000 breast-cancer survivors in the United States and China found that women who consumed more than 10 milligrams of soy isoflavones a day (the equivalent of about half a glass of soy milk) had a significantly reduced risk for breast-cancer recurrence. Soy contains antioxidants and vitamins that can benefit all women, even breast-cancer survivors. (However, these findings don't apply to all supplements; some can contain higher amounts of isoflavones.) More good news: A 2011 study in The American Journal of Clinical Nutrition reported that soy intake was associated with lower lung-cancer risk.

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Your move: Enjoy a serving a day, but don't go overboard.

Soy is like chocolate and wine--it's good in moderation. "At up to 25 milligrams per day, isoflavones have protective properties," says Edward Bauman, Ph.D., coauthor of The Whole-Food Guide for Breast Cancer Survivors. "But a soy powder or protein that has 50 or 100 milligrams of isoflavones becomes problematic because the molecular structure of the food has been interfered with." Which is why Bauman recommends sticking with one serving of whole soy (edamame, tempeh) or minimally processed soy (milk, tofu) a day and avoiding highly processed versions (soy chips, soy powders, fake-meat products), which contain concentrated levels.