Phytoestrogens are estrogens contained in plants. They have a chemical structure similar to the human hormone estrogen. They have a weak estrogen effect when eaten. The most commonly studied are the isoflavones, found in soybeans and other legumes. The word soyfood refers to any food products made from soybeans. Soyfoods provide significant amounts of isoflavones.
In addition to the possible health benefits, soyfoods are very nutritious. They are low in saturated fat, free of cholesterol, high in fiber, and rich in many vitamins and minerals. Soyfoods are high in protein.
Soy protein is the only plant protein that is considered complete. In fact, it is equivalent in quality to animal protein. Soy protein causes less calcium to be excreted from the body than animal protein does. This may protect kidney function. Soyfoods are also a good source of calcium, helping to protect the bones Soyfoods are also high in iron.
The benefits of adding phytoestrogens to the diet appear very promising. But researchers caution against adding large amounts. Too much of them may cause problems with development and fertility. No one suggests that they replace regular treatment for osteoporosis, heart disease, or high cholesterol. Plant estrogens should be avoided by people who take certain medications. These include tamoxifen, which is used to treat breast cancer.
The US Food and Drug Administration (FDA) has recently approved a food label health claim for foods that contain soy. The health claim states that soy protein may reduce the risk of coronary artery disease. For a food to qualify for the health claim, each serving must contain 6.25 grams of soy protein. It must also meet other criteria for fat, cholesterol, and sodium content. The FDA has based this on studies that show 25 grams of soy protein per day have a cholesterol-lowering effect.
Making soyfoods part of a healthy diet can be easy, nutritious, and delicious. The following foods are excellent sources of isoflavones. They provide from 30 to 50 mg per serving:
The only two soy products that do not contain isoflavones are soy oil and soy sauce.
Here are some tips for adding soy to a healthy diet:
Here's how to replace ingredients in favorite recipes with soy products:
Soy is found in numerous foods. Soyfoods include:
Research is uncovering more and more about the health benefits of eating soyfoods. Soy isoflavones may decrease the risk for heart disease. They may reduce the risk of breast cancer, cancer of the uterus, prostate cancer, and colon cancer. They seem to help prevent osteoporosis, or bone thinning. They also help control diabetes, and ease the symptoms of menopause.
During menopause, women have fluctuations in estrogen levels. These hormonal changes may increase the risk of heart disease and osteoporosis. These changes also cause hot flashes, night sweats, insomnia, and headaches. The ability of plant estrogens to reduce these symptoms is now being studied.
Author:Kimberly Tessmer, RD, LD
Editor:Duff, Ellen, BA
Reviewer:Jane Hemminger, RD, LD
Applegate, "Soy Wonder," Runner's World, 1998. Patterson, "Isoflavones: New Frontier in Nutrition," The Soy Connection Newsletter, 1998. US Soyfoods Directory, www.soyfoods.com. United Soybean Board, www.soytalk.com. Messina and Messina, Soyfood for Thought. Barret, "Phytoestrogens: Friends or foes?," Environmental Health Perspectives, 1996. Environmental Estrogens and Other Hormones: Phytoestrogens, Tulane and Xavier Universities website. Nutrition During Cancer Treatment, Flax Seed and Tamoxifen, Oncolink website. Soy and Human Health, University of Illinois website. Phytoestrogens: Hormones from Plants, Mayo Clinic website. Anderson and Deskins, The Nutrition Bible, 1995.