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United States Department of Agriculture

Agricultural Research Service

Soybean - A versatile plant food worth splurging on
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Lin Yan

Soy is an annual plant that has been a major source of dietary protein in Asian countries for thousands of years. Soybeans are high in nutritional value as a nonanimal source of eight essential amino acids, which makes them a complete plant protein.

Soy is an annual plant that has been a major source of dietary protein in Asian countries for thousands of years. Soybeans are high in nutritional value as a nonanimal source of eight essential amino acids, which makes them a complete plant protein. Soybeans contain approximately 38 percent protein, 18 percent oil, 30 percent carbohydrates and 14 percent moisture. In addition, soybean are a good source of phosphorus, potassium, B vitamins, zinc, iron and the antioxidant vitamin E.

In history, soybeans first were cultivated in China and spread to other countries. Soybeans first were grown in the United States in early the 1800s as a coffee substitute during the Civil War. During World War II, soybeans became an important source of dietary protein and edible oil in both North America and Europe.

Today, soy is one of the major agricultural crops in the United States, and America is the leading producer in the world followed by Brazil, Argentina and China. North Dakota is one of the soy-producing states in the U.S.

Scientific research in recent decades reveals that consumption of soy foods may be beneficial to human health, beyond its nutritional value as a source of plant protein. A substantial body of research has been conducted in investigating the effects of soy on heart health, which show that soy protein can help lower LDL (bad) cholesterol from 3 percent to 5 percent. This modest reduction has considerable relevance as each 1 percent reduction in LDL cholesterol is associated with a 2 percent to 4 percent reduction in heart disease risk. In 1999, the U.S. Food and Drug Administration authorized a health claim that consuming 25 grams of soy protein, as a part of a diet that is low in saturated fat and cholesterol, may reduce the risk of heart disease.

Recent studies reveal that soy may help reduce the risk of obesity and diabetes, although the number of studies is limited. Maintaining optimal control of glucose and insulin levels is essential for overall good health, especially for obesity and diabetes. Soy foods may be valuable in this regard. Soy protein intake reduces fasting serum glucose levels in postmenopausal women who are moderately high in fasting glucose levels.

Soy foods have a low glycemic index. The glycemic index refers to the relative blood glucose response to sugar-containing foods. Some evidence indicates that foods with a high glycemic index — which may cause greater rises in serum glucose and insulin levels — increase risk for chronic diseases including obesity and diabetes. Thus, the low glycemic index of soy foods suggests that they have a role to play in helping control obesity and diabetes. Furthermore, there have been studies showing that soy-based meal as a dietary replacement promotes weight loss and reduces blood cholesterols in obese subjects.

Menopause is the permanent ending of menstruation, which coincides with osteoporosis and hot flash. Osteoporosis is a disease of bone with chronic loss of bone minerals, which leads to an increased risk of fracture. A hot flash produces a sudden sensation of warmth or even intense heat that spreads over various parts of the body, especially the chest, face and head.

There is considerable interest in the skeletal benefits of soy. This is because soy intake is associated with higher bone mineral density in Asians. Results from human clinical trials generally support this observation.

More than 25 clinical trials have been conducted regarding soy and hot flash. It is recommended that women with frequent hot flashes (more than five times per day) try soy foods for the relief of menopausal symptoms. While results are not consistent across the studies because of differences in study design, number of participants and the duration of the intervention, improvements generally are seen within three to four weeks in studies showing a reduction in hot flash.

There has been much focus the past 20 years on the cancer-preventive effects of soy foods. Cancer is a group of diseases characterized by the uncontrolled growth and spread of abnormal cells. Population studies show that consumption of soy foods is associated with about 14 percent reduction in breast cancer risk in women and about 30 percent reduction in prostate cancer in men. Most of these studies were conducted in Asian countries, where the soy consumption is higher than that in Western countries.

We have a variety of soy foods in grocery stores and food markets. These foods generally can be assigned into two categories, traditional and nontraditional. Soy milk and tofu (bean curd) are the most commonly consumed traditional soy foods. Soy milk is directly processed from water-soaked soybeans, and tofu is curdled from soy milk with mineral salts. Miso is another popular traditional soy food in Japan. It is a fermented soybean paste that is used as a soup base.

Soy flour, soy protein concentrate and soy protein isolate are the three most popular nontraditional soy foods.

It is easy to incorporate soy into a daily diet. Green soybeans, sometimes called edamame, are found in the frozen vegetable section in supermarket. They can be used in recipes the same way beans are used. Soy milk is available in plain or flavored, for example, vanilla and chocolate. Drink it plain, add it to breakfast cereals, make oatmeal with it or add it to coffee, shakes and smoothies.

Plain tofu comes firm or soft. Add the firm to stir fries, casseroles and other entrees to replace meat, and add the soft ones to soup, sauces, dips or spreads. Soy flour works well to replace wheat flour in bread and muffin recipes. Furthermore, soy burgers and other ready-to-eat meat-alternatives made with soy protein are widely available in marketplaces.

The options for adding soy to the diet have never been better — even creamy frozen desserts are made with soy.

So splurge!

Last Modified: 3/4/2009
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