Soy: Magic Bean or Tragic Bean?

Wednesday, April 13, 2011 | 0 comments »

By Denis Faye

This just in: Soy prevents cancer. Soy lowers "bad" cholesterol. Soy prevents osteoporosis. Hooray! Bring on the tofu!

Wait! More breaking news: Soy suppresses thyroid function. Soy hinders testosterone. Soy causes cancer. Oh, no! Looks like it's back to beef burgers for me.

Welcome to the food wars. On one side, big business tells us what to eat. On the other side, watchdog groups tell us we're being poisoned. From the wings, the media screams about the battle at the top of its lungs. In the middle stands our poor diet, constantly scrutinized. Sooner or later, everything we eat is either branded the next superfood fad or the devil incarnate. Every now and then, a food comes along that gets to be both. Ladies and gentlemen, I give you soy.

Then and now

The soybean, which comes from East Asia, made its way to the United States in 1804. Through the 1930s, its primary use was as livestock feed. But in the last 70 years, things have changed. America is now the world's foremost soybean producer, and from an economical standpoint, soybeans are one of the world's most important legumes.

In much the same way one of America's other big crops, corn, has found its way into just about every packaged food in the country in the form of high-fructose corn syrup, the food industry has come up with all kinds of inventive uses for soy. It's used to make paints, glues, bug sprays, and food. And we're not just talking tofu here. From soy milk to cereals to protein bars to meat substitutes, the stuff is everywhere.

The good news and the bad news

Because the soybean is such an economic powerhouse, it's often in the spotlight. The FDA states that soy is a "complete protein," meaning that it's just as good as meat, eggs, and dairy in fulfilling your amino acid needs. Is this true, or has the soybean lobby just leaned on the FDA to say that? And what of the "miracle food" claims—are they true?

Of course, these positive claims are followed by crusaders who are attempting to bring down the soy monolith. How can these opposing claims also be true? After all, scientific studies are infallible, right?

Not so much. It's an incredibly difficult topic to get the straight dope on, and an incredibly easy topic to manipulate. So trying as best as possible not to buy into any hype, let's take a look at soy.

The Asian argument

The first argument out from the pro-soy lobby is, "Look at Asia! They've been eating soy for centuries and they're super-healthy!"

Generalizations aside, this is true, except Asian cultures don't go all Coneheads on the stuff, consuming vast quantities. A 1990 study from Cornell University concluded that the average Chinese diet consisted of between 0 and 58 grams of soy a day, with the average being 13 grams—or about half an ounce.

In much the same way that the French can pull off eating creamy cheeses and chocolate and remain thin, the secret to eating anything, healthy or decadent, is moderation.


Above and beyond any claims that soy is a miracle cure for anything, it's important to remember that its primary function in most people's diets is to provide a lean, meat-free protein. How well does it do this? According to the Food and Agriculture Organization and World Health Organization (FAO/WHO), it does just fine.

In 1989, the FAO/WHO developed the Protein Digestibility Corrected Amino Acid Score, a method of measuring protein values in human nutrition. Eggs, milk, and soy all score a 1.0, the best possible. Beef scores .92 and peanuts score .52.

So purely from a macronutrient standpoint, soy looks to be good stuff. Yet for some reason we seem determined to ruin it. Sure, the protein is still there in soy sausage or fake bacon or faux chicken, but now there's also sodium, plus the huge laundry list of chemicals it took to morph the soy into resembling the food it's trying to imitate or replace. A tolerable soy burger has 230 mg of sodium—10 percent of the recommended daily allowance. An even saltier option, like the 2.5 oz. Boca Burger® All American Classic, has 500 mg. By way of comparison, a 2.5 oz. beef patty only has about 55 mg of sodium.

So if you're looking for protein, stick to soybeans, tofu, and soy milk and leave the meat substitutes alone.


Soybeans are also one of the very few nonanimal sources (along with flax and canola) of omega-3 fatty acids, which help the body with brain function, as well as growth and development. So especially for vegetarians, consuming soy to get your omega-3s is worth considering.

Fermentation celebration

There's also a school of thought that believes fermented soy, such as that found in miso, natto, tempeh, and pickled tofu, is nutritionally superior to unfermented soy. Notable research includes a 2010 study out of the Korean Food Researches Institutes showing that fermented soy has positive effects in combating type 2 diabetes. However, the notion that fermented soy is more easily digestible than regular soy is unfounded. If you want to include fermented soy—much of which can be an acquired taste—in your diet, that's great, but choosing to choke down a bowl of natto instead of a bowl of edamame isn't going to be that much more healthful, so don't do it if you don't want to.

Miracles and scares

Most of soy's miracle claims and scares are based on rather flimsy studies. For example, a study in the Archives of Internal Medicine showed that among 24,403 postmenopausal Chinese women, those who ate soy-heavy diets had a 37 percent lower risk of broken bones. That's good news until you look at the findings in a cultural context, as the watchdog group the Center for Science in the Public Interest pointed out in their newsletter, Nutrition Action. American women consume considerably more dairy than Chinese women, which has a huge influence on their relative bone strength. Furthermore, according to the University of Washington Medical Center, Caucasian women are historically more prone to hip fractures than Asian women, so the CSPI study is pretty much moot.

As for studies indicating that soy can lower LDL or "bad" cholesterol levels, a 2005 review sponsored by the U.S. Department of Health and Human Services' Agency for Healthcare Research Quality showed that to see a measly 3 percent reduction in LDL, one had to eat a pound of tofu a day.

As for the scares, the much-ballyhooed 1985 USDA Trypsin Inhibitor Study showed that rats on a primarily soy diet had an increased risk of pancreatic cancer. It's all really scary until you learn that a rat's pancreas has a sensitivity to dietary protease inhibitors, a substance in soy that inhibits digestion of proteins. Humans have no such sensitivity. In other words, rat pancreases and human pancreases are different enough to call the study into question.

As you can see, for every source that seems to support one side of the pro-soy/anti-soy debate, there seems to be an equal and opposite source that refutes its claims.

Isoflavone of the month

One thing everyone agrees on is that soy is loaded with isoflavones, an organic compound that is thought by some experts to be an important element in helping to fight cancer. There have been studies that suggest the isoflavones in soy may help prevent prostate cancer, hot flashes, osteoporosis, and brain aging. So why not consume as many isoflavones as you can? Well, there's also a downside.

Isoflavones are a type of phytoestrogen, a plant-produced chemical that acts like estrogen when introduced into animals' bodies. Although studies in 2001 and 2006 suggest that women with a high risk of breast cancer should be mindful about the amount of soy they consume, a study presented at the American Association for Cancer Researche in Orlando, Florida, in April 2011, which compiled data from 18,000 women diagnosed with invasive breast cancer, found no difference in terms of recurrence and death between women who consumed a lot of soy and women who consumed very little. If anything, those who consumed greater amounts of soy had, statistically, an insignificantly lower risk either of recurrence or of succumbing to their disease.

There are also several studies that suggest it's a bad idea to give infants soy formula because of the isoflavones—but before anyone freaks out, there are also several studies that say soy formula isn't a problem at all.

How much is too much?

Before giving up on soy completely because you just can't be bothered with the data, consider this alternative: moderation. The Center for Science in the Public Interest suggests limiting soy consumption so you ingest about 50 to 70 milligrams of isoflavones a day. That's one or two cups of soy milk or 6 to 9 ounces of tofu. That should be enough to tap the benefits without overdoing it.

But also keep in mind that because the soy industry has become so huge in the United States, food manufacturers can acquire it cheaply, so they're looking to find ways of using it in as many different products as possible. Whenever you're buying some kind of processed food, make sure to read the ingredients. You're probably eating more soy than you realize.

Even if there weren't concerns about soy, the amounts I just specified—one to two cups of soy milk or 6 to 9 ounces of tofu per day—would still be good numbers to shoot for. Regardless of whether or not a food is the miracle nutrient of the moment, eating excessive amounts of anything is pretty much never a good idea. If you focus on one thing too much, you're neglecting a myriad of other important nutrients—the balance of which will make for great health.