Soybean or soy products are a nutrient-dense source of protein that can safely be consumed several times a week, and probably more often, and is likely to provide health benefits—especially when eaten as an alternative to red and processed meat.
In half of a cup of soybeans, there are 16 grams of protein, along with a good amount of vitamin B6, vitamin B2, vitamin B1, Vitamin K, folate, potassium, magnesium, manganese, copper, selenium, phosphorus, iron, and calcium
What do the studies say?
Studies present conflicting conclusions about soy, but this is due to the wide variation in how soy is studied. Results of recent population studies suggest that soy has either a beneficial or neutral effect on various health conditions.
Soy is unique in that it contains a high concentration of isoflavones, a type of plant estrogen (phytoestrogen) that is similar in function to human estrogen but with much weaker effects. Soy isoflavones can bind to estrogen receptors in the body and cause either weak estrogenic or anti-estrogenic activity. The two major soy isoflavones are called genistein and daidzein.
Soy isoflavones and soy protein appear to have different actions in the body based on the following factors:
Type of study. Is the study with animals or humans? Soy may be metabolized differently in animals, so the outcomes of animal studies may not be applicable to humans.
Hormone levels. Because soy can have estrogenic properties, its effects can vary depending on the existing level of hormones in the body. Premenopausal women have much higher circulating levels of estradiol—the major form of estrogen in the human body—than postmenopausal women. In this context, soy may act as an anti-estrogen, but among postmenopausal women, soy may act more like an estrogen. Also, women with breast cancer are classified into hormone types—either hormone-positive (ER+/PR+) or hormone negative (ER-/PR-) breast cancer —and these tumors respond differently to estrogens.
Type of soy. What type of soy is being studied: Whole soy foods such as tofu and soybeans, processed versions like soy protein powders, or soy-based veggie burgers? Fermented or unfermented soy foods? If supplements are used, do they contain isoflavones or soy protein?
Thus, there are many factors that make it difficult to construct blanket statements about the health effects of soy.
Moderation: the key to Consuming Soy
Following the recommendations of NCCIH and the American Association of Family Physicians, men and women should eat soy in moderation. This means that adult men and women should limit soy to 25 grams a day. This means you can have one to two servings of soy products a day, like a cup of soy milk or four ounces of tofu. A reasonable recommendation for those under 18 would be about half this amount or 12 to 13 grams of soya each day.
Prefer Whole Soy Foods over Processed
While foods made using whole soybeans like edamame, tofu, and soy milk have health benefits, highly processed products likely do not. Some food companies have separated protein from whole soybeans and used it to make soy protein isolate. They’ve packed this isolate into shakes and turned it into meat substitutes. Unfortunately, soy protein isolate may not be healthy. In fact, it’s been shown to increase the amount of insulin-like growth factor in the blood, just like cow’s milk. The insulin-like growth factor can promote cancer growth. So stick to simple soy products like tofu, tempeh, edamame, soy milk, or miso. These foods may help protect against cancer while providing health benefits.
Focus on tofu, tempeh, edamame, soy milk, and miso as part of a balanced, plant-based diet.