Soyfoods and Nutrition

Soybeans and the foods made from them (soyfoods) are members of the legume family. Like other legumes, soyfoods are packed with vitamins and minerals. However, they also have a unique nutrient profile. Although they are a carbohydrate-rich food, they are lower in carbohydrates than other legumes. It is the protein content of soyfoods that makes their nutritional profile remarkable.

Protein

Soybeans are higher in protein than other legumes and most other plant foods. About 35 percent of the calories in soy are from protein. The protein in soy is also high quality, which means it is well suited to human physiological needs. When protein from different foods including beans, meat and dairy foods are ranked, soy gets the highest possible rating and is as good a source of protein as meat and milk.

A special advantage of soy protein is that it may help to lower blood cholesterol levels. When soy protein replaces protein from animal foods in the diet, cholesterol levels are reduced. The effect is best in people who already have high cholesterol levels. It may also help to raise the levels of HDL-cholesterol (the "good cholesterol") in the blood. Over the past 30 years, more than 40 studies have shown the effects of soy protein on cholesterol levels.

Fat

The fat in soybeans is mostly polyunsaturated. Soybeans are low in saturated fat and, like all plant foods, contains no cholesterol. Soybeans also contain a special type of polyunsaturated fat called omega-3 fatty acid. This type of fat is essential in the diet and may help to reduce risk for cancer and heart disease. Soybeans are one of the few plant foods that provide significant amounts of this fat.

Many soyfoods are lower in fat than the whole soybean. Textured soy protein is essentially fat-free and so is defatted soy flour. Some brands of soymilk and tofu are also reduced in fat.

Although many soyfoods are higher in fat than other legumes, they are sometimes lower in fat than the foods they replace. Using textured soy protein in place of ground beef - or to replace half of the ground beef - in chili or spaghetti sauce can reduce fat content of a serving by 10 to 20 grams. It also reduces saturated fat and cholesterol. Tofu can be mixed with ricotta cheese for use in stuffed shells or lasagna to reduce saturated fat and cholesterol.

Fiber

Soybeans are rich in fiber. Diets high in fiber can help reduce the risk of some cancers and heart disease. Americans consume only one-half the recommended amount of fiber. One-half cup of soybeans contains 8 grams of fiber, which is more than one-third the minimum amount recommended. Soyfoods made from the whole soybean - tempeh, textured soy protein, and soy flour - are rich in fiber. Others like tofu and soymilk have the fiber removed.

Vitamins and Minerals

Soyfoods are rich in several B-vitamins. Some soyfoods are good sources of the B-vitamin folacin. Many people may not get enough folacin in their diets, which may be one risk factor for heart disease. Soyfoods are also good sources of the B-vitamin niacin and vitamin B6.

Although many soyfoods are rich in iron, the iron may not be very well absorbed by the body. The iron in soyfoods that are fermented - tempeh and miso - may be better absorbed than the iron in other soyfoods. Also, the iron in soy-meat blends appears to be well absorbed.

Calcium is another nutritional characteristic of soy. One-half cup of soybeans contains almost 90 milligrams of calcium, which is about 10 percent of the RDA for this nutrient. Roasted soynuts, textured soy protein and tempeh are also good calcium sources. Processing increases the calcium content of some soyfoods. For example, some tofu is made using a calcium salt, making this type of tofu rich in calcium. Soymilk is sometimes fortified with calcium.

Soyfoods and Disease Prevention

In addition to being nutritious, soyfoods may play a role in supporting better health. Soybeans and the foods made from them are rich in special compounds called isoflavones. Soyfoods are the only foods that contain significant amounts of these compounds. The isoflavones may help to reduce risk for heart disease and may also support better bone health.