You may have heard about soy foods in the news, including claims that soy prevents diseases such as cancer and heart disease. So what is the story on soy? Read on for some facts.

What Is Soy?

Soy, a versatile bean used mostly in Asia, is found in foods like soy milk, soy sauce, miso (soybean paste), tempeh (which is kind of like a soy cake), and tofu. Soy is also sometimes added to foods like breads, cereals, and meat products, and used as a meat substitute in products such as soy burgers and soy hot dogs.

Foods that contain whole soy are a good source of protein for vegetarians and vegans because they provide all the amino acids - a type of nutrient - that people need to stay healthy. (People who eat meat get all their essential amino acids from meat products.)

What Are the Benefits?

Americans have started adding more soy to their diets in recent years because scientific studies have shown that some soy products offer health benefits. These include lowering cholesterol and reducing a person's risk of heart disease. But be aware that the health claims you see made about soy are not necessarily for all soy foods - they just apply to soy protein. This means that only foods identified as being "whole soy," or foods that specify they contain soy protein, will offer these health benefits.

Whole soy foods are a great source of protein and contain other nutrients, such as fiber, B vitamins, and omega-3 fatty acids. Foods containing soy protein are also a healthy alternative to meats and other animal products that contain cholesterol and saturated fat.

Studies have produced varying results regarding certain health benefits of soy, particularly whether soy helps to prevent diseases such as cancer. Groups such as the American Dietetic Association (ADA) and the Food and Drug Administration (FDA) do agree, though, that diets that include 25 to 50 grams of soy protein a day can help to lower levels of LDL cholesterol. LDL cholesterol - which is sometimes referred to as "bad cholesterol" - is the type of cholesterol that is known to build up in and to clog blood vessels, leading to an increased risk of heart disease.

Soy in Your Diet

In addition to the important soy protein factor mentioned above, some soy foods may not offer the other benefits you think. For example, soy milks may not be as good a source of calcium as regular cow's milk: Soy milks need to be fortified with calcium. And even with calcium added, experts believe they are less effective sources of this mineral than cow's milk.

If you're concerned about the amount of fat in your diet, keep in mind that soy foods do contain some fat. For example, a serving of tofu (about 1/2 cup, or 118 milliliters) contains 5.5 to 6.5 grams of fat. However, most of this fat is unsaturated, meaning it won't clog arteries. If you're still worried about fat, though, you can opt for a low-fat version. A serving of low-fat tofu has about 1.5 to 2.5 grams of fat.

If you're interested in eating more soy, the ADA recommends gradually introducing soy into your diet - for example, by mixing soy flour with regular flour. The key to good health is to eat a wide variety of nutritious foods without focusing too much on any one food.

Soy foods that pack the highest protein punch include soy flour, tempeh, and tofu. When selecting soy foods, the FDA recommends checking food labels to ensure that the food is an adequate source of soy protein and is low in saturated fat and cholesterol.

Reviewed by: Mary Frances Picciano, PhD
Date reviewed: September 2004