Soy: 10 questions answered!
Do we eat too much of it? In a word: Yes. Whether it's healthy or not, soy is being forced down our throats a lot more than we know. The U.S. is the largest producer of soybeans in the world, so there's a lot of money there to spend on ways to tell us how good it is for us. But even if it is good, that's no reason to eat nothing else. Americans eat more soy than anyone else in the world, with some people getting upwards of 60 percent of their protein from it. This is because it's in a lot more than tofu these days. The food industry has developed so many creative uses for soy that it's now found in paints, glues, and bug sprays. And food. A lot of it. Soy, in some form or another, is on the label of hundreds of varieties of processed foods, which, by most accounts, seems to be the real problem.
But haven't healthy Asians been living on it for years? This is the marketing hoopla, for sure, beginning with the dubious claim that all Asians are healthy. Either way, however, soy plays only a partial role in their diets. 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—about half an ounce. This is not insignificant, but it's a long way from being 60 percent of their protein consumption.
Are all types of soy the same? Not exactly. You don't need a nutrition expert to point out that there might be a difference between an unprocessed soybean and bug spray. But soy is now found in foods from all over the tiers of Michi's Ladder, and it can be found on Tier 1 or Tier 5. For example, natto—a Japanese dish of fermented soy—nearly always shows up on lists of the world's healthiest foods. But soy chips are, well, fried crispy things devoid of nutrition, no matter what the base ingredient is. The rule with soy should be the same as the rule with most other foods; the closer it is to nature, the better. This means that edamame and miso are likely to be healthier than soy milk, soy cheese, soy burgers, and soy ice cream.
Can it cause cancer? Forget sperm count; let's first find out if it's going to kill me! The risk of breast cancer due to soy intake has proliferated on the Internet since a 2001 Canadian study and a 2006 California study suggested that women with a high risk of breast cancer be mindful about the amount of soy they consume. This was due to isoflavones, which are a type of phytoestrogen, a chemical produced in plants that acts like estrogen when introduced into animal bodies. The isoflavones scare has caused both Israel and Great Britain to issue warnings recommending that females under the age of 18 limit their soy consumption.
Can it prevent cancer? On the flip side, there's a lot of research showing that soy isoflavones might help prevent cancer, along with hot flashes, osteoporosis, and brain aging. According to 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, it seems far more likely that soy prevents rather than causes cancer. "There is very exciting data indicating [that] 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."
Is it making us sterile? Back to the original scare piece, we see that even small amounts of soy consumption can lead to a reduced sperm count. Researchers at Harvard concluded that eating only half a serving per day (about the same as the Chinese, who haven't seemed to have problems) lowers sperm concentrations and "may play a role" in male infertility. However, moving past the headlines, we see that no males in the study were infertile due to soy and that the much larger culprit in the study was obesity. Obesity can cause sterility. There is no evidence that soy can or will.
Is it making us fat? One soy fact is clear: It's not making us fat. Soy's popularity, in fact, came from the fact that it's a very good source of protein and omega-3 and, unlike animal protein, is far less likely to make us fat. 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. Additionally, soy's fat is mainly omega-3, making it an excellent substitute for meat, which is high in saturated fat.
Isn't an allergy to soy likely? Soy is one of the top eight allergens, along with milk, eggs, peanuts, tree nuts, fish, shellfish, and wheat. This is due to its 12-protein structure. While it's not likely that you're allergic to soy, its symptoms can be subtle and hard to distinguish, like sore muscles or general fatigue. Also, it's in so many foods that it can be difficult for those with soy allergies to eat a balanced diet, or to even know they're eating it at all. Soy is often found in baked goods, canned tuna, cereals, crackers, sauces, soups, some peanut butters, and infant formula. Avoidance takes a lot of attention.
What is soy lecithin? It seems to be in everything! Soy lecithin is a waste product that comes from the manufacturing of soybeans and is used in many different products. Its main use is as an emulsifier in junk foods, but it's also used, in part, for many supplements. It's been linked to many health benefits and some things less beneficial. It's debatable whether it's a health benefit or a danger, but a bad batch was linked to a recent Hershey recall and plant closure in 2006. Even if it proves to be healthy, as studies suggest, soy lecithin still needs to be considered when determining your soy intake.
So why risk eating soy at all? And if I do, how much should I eat? There is no denying that soy can be a healthy part of your diet, unless you happen to be allergic to it. Its macronutrient profile is exceptional. It's a great protein and fat source. It's been linked to improved cardiovascular health, and the isoflavones have myriad benefits associated with them. All the negative research seems to be linked to excessive amounts. It's only what is deemed excessive that is debated. Messina states, "I don't believe there is evidence that exceeding these amounts is harmful," in regards to a 25-gram-per-day recommendation. The Chinese study showed nothing but health benefits associated with the consumption of 13 grams per day, on average, but participants also ate up to 58 grams per day. It would make sense to recommend a serving or two of soy per day, provided it comes from natural sources. The trick is learning about the foods wherein soy is hidden, which will take some label reading and a little bit of probing.
Steve Edwards (2008). Soy: 10 questions answered. Retreived from Newsletter Archive: Healthy Protein Sources.