Soy Vey! Should you eat it or not?

One sit-down review of the current research on soy can leave you with information as mercurial as a teenager’s emotions. Soy is a hot topic—and sometimes a controversial one—among researchers and consumers alike.

One moment, you’re told you are doing your preteen daughter a favor by giving her soy because it reduces her risk of getting breast cancer at an older age by a whopping 58 percent. The next, you hear that soy may stimulate the onset of early puberty. Which is true?

The answer lies in how you interpret the data. It’s not uncommon for studies to yield contradictory conclusions about whether soy consumption helps prevent or causes chronic disease.

Bottom line, most scientists try to avoid anecdotal evidence despite many soy enthusiasts out there shopping the grocery aisles. Then comes a pecking order of sorts in interpreting the researchers: The first stop is animal studies, followed by human studies.

Food scientists most often interpret animal research as just that: True for the animals, and perhaps indicating the need for human trials. Human studies, then, are the most relevant when it comes to fully understanding the effects of soy on overall human health.

And—drum roll, please—it turns out that, so far, the majority of those studies suggest soy is a safe addition to your diet.

Soy Yes: Good for your cholesterol ratio and for lowering breast cancer risk among teen girls.

Non-fermented whole soy is a complete protein. This, above all else, is its primary benefit. It contains omega-3 fatty acids in a form similar to that found in flax seed rather than what’s found in fish. Because it is an excellent source of protein, soy can replace foods in the diet that are high in saturated fats.

“The amino acid balance is excellent—and for a plant source of protein, that is rare,” says John Erdman, professor of food science and human nutrition at the University of Illinois at Urbana-Champaign. “It is relatively low in saturated fat and it contains no cholesterol. Soy versus other animal sources of protein can reduce serum cholesterol levels [your LDL or “bad” cholesterol]. Some studies show you may even see an elevation of HDL [your “good” cholesterol].”

The American Heart Association recently concluded that soy, once thought to have an enormous effect on cardiovascular health, instead has a modest effect. Soy proteins are thought to lower a person’s bad cholesterol somewhere between 3 percent and 5 percent.

“We used to think that it lowered cholesterol by 10 percent,” says Mark Messina, an associate professor at Loma Linda University who has worked with the National Institutes of Health and the National Cancer Institute, and now consults as a soy expert. “Now we know that number is lower. But even though soy protein lowers cholesterol less than we previously thought, since every 1 percent decrease in LDL lowers heart disease risk from 2 to 4 percent, even a 3 to 5 percent decrease is relevant.”

Another benefit of soy appears to be that of preventing breast cancer when consumed by adolescent girls.

“There is very exciting data indicating early soy consumption reduces breast cancer risk,” says Messina. “There have been four epidemiologic studies that have looked at this relationship. The latest study, from the National Cancer Research Institute, found that women who consumed the most amount of soy at 5 to 11 years old were 58 percent less likely to develop breast cancer than women who consumed less soy.”