Soy Vey! Should you eat it or not?
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The data is confusing and contradictory, but there are soy-savvy guidelines you can follow.
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.”
Soy What? Soy is a top allergen, debate about estrogen-like effects and why there are soy warnings in Great Britain and Israel.
Soy is one of the top eight allergens, along with milk, egg, peanut, tree nuts, fish, shellfish and wheat. Soy is a hidden ingredient in so many foods that it can be difficult for those with soy allergies to eat a balanced diet. Some individuals who are allergic to soy don’t always know they are eating it. Soy is often found in baked goods, canned tuna, cereals, crackers, sauces, soups, some peanut butters and infant formula. Soy as an allergen is a point agreed upon by all.
One point of major debate is the effect of the isoflavones soy contains. The issue with these plant-based estrogens is whether they affect the human body the same way true estrogen would. So far, studies done in rats, using high doses of soy different than that found in whole soy foods, show that isoflavones could have the same effect as estrogen. But remember the hierarchy of research: Human studies indicate that isoflavones do not mimic the negative effect of estrogen unless a cancer tumor is already present in the person eating the soy.
Health organizations in Israel and Great Britain have issued warnings to limit soy consumption for children up to age 18, based on estrogen-mimicking study results in rodents. Soy researchers note, however, that rats and humans process isoflavones differently, and rat studies don’t offer information on how isoflavones affect people.
“There is no human evidence indicting isoflavones [in a supplement or food form] have adverse effects,” says Messina. “Rodents metabolize isoflavones differently than humans and most often these toxicologic studies use pure genistein [a type of isoflavonoid derived from soy products] that is injected. They are not examining soy foods.” Erdman agrees that these studies do not indicate soy is unsafe for humans, given the differences between how rats and people metabolize plant estrogen.
Soy What? Part 2: Potential for easing menopause symptoms, the “Internet issue” of fermented versus non-fermented soy, and how you might be blocking minerals from your body.
The jury is still out on whether soy has any meaningful impact on helping ease menopause symptoms, or on reducing cancer risk for adult soy consumers. The confusion between eating fermented versus non-fermented soy, says Messina, has been discussed a lot online, but lacks any research to back up whether fermented soy is a healthier choice.
And there have been no human studies that prove soy causes precocious puberty in adolescent girls, a reduction in sex drive for adult men and women, or an increase in risk of thyroid cancer—all health issues red-flagged by anti-soy experts.
Phytates and trypsin inhibitors both are found in soy foods. Phytates are antioxidants, but they also inhibit mineral absorption. Messina says calcium absorption from fortified soymilk is similar to the absorption of calcium from dairy milk, despite the phytates. But—and this is an important “but” to some people—phytates do lower iron and zinc absorption.
Trypsin also is a mineral absorption inhibitor. It is inactivated by heat, so it’s better to consume heated tofu rather its raw counterpart. This means don’t blend raw tofu into a smoothie or a dessert treat and expect to yield the same nutritional benefits. And be sure to heat your edamame (the bean inside soy pods) before popping it in your mouth.
Soy Now: How much soy is right for you?
Moderation and variety are rules of thumb when it comes to good nutrition. These guidelines are no different with soy, and as with most foods, researchers suggest you consume whole soy products rather than processed soy products.
That means edamame or tofu rather than soymilk, just as it is a healthier choice to eat apples over applesauce, says Messina. The less processing—and fewer added ingredients—the better.
Experts who raise red flags against soy suggest adults and children eat soy infrequently, perhaps no more than a couple of times a week. One reason is that soy might be present or “hidden” in other processed foods.
Pro-soy experts suggest adults eat up to 25 grams of soy protein and 100 milligrams of isoflavones daily. This translates to about two to four servings a day. A serving is 8 ounces of liquid, such as miso and soy milk, or about half a cup of solid soy such as tofu, tempeh and edamame.
“I don’t believe there is evidence that exceeding these amounts is harmful,” says Messina. “But because common dietary advice is to get nutrients—and protein in this case—from a variety of sources it could be argued that consuming more than 25 grams of soy protein would be putting too much emphasis on one food.”
For children, no more than two servings of soy per day is recommended, equal to the half-cup of solid soy or 8 ounces as a soup or milk. Be sure to monitor how much sugar your child is getting with the soy. Often there can be as much as 16 grams or higher per serving added to make soy milk taste better. The effects of too much sugar? That’s a different story and research hierarchy.