Most doctors recommend no more than one to two servings of soy milk per day. Soy milk is a dairy milk substitute made from pressed soybeans. Soy milk, tofu and other whole, fermented soy products are the best sources of soy protein.
Patients with thyroid and gastrointestinal disorders should not consume soy without a doctor's approval. Studies have shown that soy may interfere with the ability of the gastrointestinal tract to absorb certain medications. High consumption of soy can also result in the overproduction of estrogen. Excessive estrogen levels have been linked with breast cancer by the National Institute of Environmental Health Sciences.