The US Food and Drug Administration (FDA) has recognized soy protein for heart health, but at the same time has included soy in the Poisonous Plant Database. A search for the word soy in this base gives 256 titles including studies warning of the association of soybean consumption with thyroid disorders, growth disorders, amino acid deficiency, mineral malabsorption, endocrinopathy and carcinogenesis from the book: The Whole Soy Story p31.

All types of soybeans contain toxins and antinutrients (substances that prevent the benefit of a food item). These substances are found in a natural way to prevent birds and insects from eating large quantities of them. The most prominent of these articles are:

Allergens: Soy is one of the eight allergens.
Goitre: Substances that affect the functioning of the thyroid gland.
Lectins or hemoglobins, which are substances that cause red blood cells to stick together, forming clots that affect the fluidity of the blood and the functioning of the immune system.
Oligosaccharides: Substances that cause flatulence and gas formation.
Oxalates: Substances that prevent the maximum utilization and absorption of calcium, and are associated with the formation of kidney stones.
Phytates: substances that affect the absorption of calcium, such as zinc, iron and calcium.
Isoflavones: A type of plant estrogen that acts like a hormone and affects the reproductive and nervous systems.
Protease inhibitors: substances that interfere with digestive enzymes and lead to poor absorption of proteins and exhaustion of the digestive system, especially the pancreas. Although many foodstuffs (legumes, some grains, nuts, seeds and some vegetables) contain these inhibitors, normal cooking processes eliminate these inhibitors, but in the case of soybeans the inhibitors remain effective even after cooking and are only eliminated through processing and fermentation Soybeans in products like tofu and tempeh
Saponins: They stick to bile, may lower cholesterol, and may damage the intestinal lining.