Traditional Soy vs. Industrial Soy

Traditional soy is fermented and therefore is more easily digested. Examples include soy sauce, tofu, and miso. Industrial soy is processed or cooked and often damaged through oxidation. Examples include soybean oil, isolated soy protein in protein shakes and bars, low-carb snack foods, and soy milk and yogurt.

Soy is an incomplete protein. Although it has all 20 amino acids, it only contains trace amounts of cysteine and methoinine. The body cannot make methoinine. It can make systeine, but only from methionine. Only animal products contain high-quality protein, with the right amount and proportion of all the amino acids. Incomplete proteins are problematic because when the diet lacks amino acids, it ransacks its own tissue to find them.

Soy went mainstream with the rise of the “heart-healthy” diet. To reduce the risk of heart disease, the US government recommends consuming 25 grams of soy protein per day in conjunction with a diet low in saturated fat and cholesterol. Soy isoflavones are antioxidants, and its amino acids regulate insulin levels. Soy may also prevent osteoporosis, hot flashes, prostate cancer, and some breast cancer.

Like all legumes, soybeans contain phytic acid, an antinutrient which reduces the absorption of vital minerals such as calcium, iron, magnesium, and zinc. It should be no surprise that diets high in phytic acid stunt growth. To add insult to injury, soy contains protease inhibitors, chemicals which interfere with protein digestion by blocking protease enzymes that break it down. Cooking reduces phytic acid and protease inhibitors, but fermentation is a better method (fermented tofu contains more available iron).

Soy is said to contain vitamin B12, but that is misleading as it actually contains a compound which resembles B12; this compound cannot be used by the body. True B12 is found only in animal foods, with one partial exception—some B12 is created during fermentation by microorganisms (tiny animals).

The problem with soybean oil: It is pressed under great heat and pressure, and the pulp is treated with solvents like hexane to extract the last drops of oil. The oil may be washed in lye (think soap!), deodorized, and bleached. Surprise, surprise… the resulting soybean oil is oxidized and carcinogenic. Annually, Americans consume 18 billion pounds of soybean oil; some 75% of the oil they consume. If you must use soybean oil, look for cold-pressed oil from organic soybeans; its polyunsaturated fats and vitamin E are undamaged. Unfortunately, soybean oil is 53% linoleic acid (LA), an omega-6 fat, and Americans already eat too much LA.

So how is soy protein isolate made? When soybean oil is made, soy producers transform the remaining protein into the key ingredient for imitation sausages, milk, cheese, etc. The processes used to derive this 90% protein isolate depletes vitamins and the amino acid lysine, but leaves aluminum reside. Soy protein does not have GRAS (Generally Recognized as Safe) status by FDA standards.

Due to soy’s high levels of isoflavones (plant estrogens), it has been used as a natural remedy for menopausal symptoms. But several recent studies have found that soy isoflavones were no better than placebo for treating hot flashes. Additionally, consuming 60 grams of soy protein daily for only one month can disrupt menstrual cycles. Regarding soy and breast cancer, studies are unclear. Some researchers believe soy prevents breast and prostate cancers, while others suggest it causes both. Genistein, the main isoflavone in soy, is toxic to the thyroid in excessive amounts; the thyroid regulates appetite, metabolism, mood, and libido. There is also evidence that certain isoflavones in soy are toxic to estrogen-sensitive tissues. Studies confirm that soy causes hypothyroidism and goiter in babies, and soy in formula may stunt growth and disrupt hormones, sexual development, and immunity.

So what should we do? Avoid all industrial soy. Do not feed soy to babies or children. If you are going to enjoy this unique legume, do so in the traditional way—it’s more digestible, nutritious, and tasty.

Please note that most of the information in this post was taken from Nina Planck's Real Food: What to Eat and Why.