Historic And Current Use Of Soy Beans

For centuries, soybeans and soybean products have been the chief source of protein for millions of people in the Orient. The soybean is native to Eastern Asia, playing a significant nutritional role in that region as does wheat in the United States.

Although the food use of soybeans in the Orient goes back to ancient times, their history in the Western World dates from the 20th century, with demand increasing as markets developed for the oil and later for the high-quality soybean meal used as a protein source for animal feeds. The industry that produces soy protein products for human consumption has grown enormously since the late 1950s. Current population is about one billion pounds of protein products for human consumption per year in the United States - or about four to five pounds per person.

Human and animal studies have shown soy products to be excellent sources of protein. In most food applications, soy protein products are not used as the sole source of protein, but in combination with other proteins. Many studies have shown soy protein products effectively improve the nutritional value of the food, especially when combined with proteins of cereal origin.

Some have suggested that, when used as the sole source of protein, soy protein products could be limiting in methionine. However, methionine supplementation of soy protein products in an adult diet is not usually necessary because, at levels normally consumed, soy protein products supply more than an adequate amount of essential amino acids, including methionine.

Both human clinical studies and animal research have demonstrated that soy protein products are comparable in digestibility to other high-quality protein sources, such as meat, milk, fish and egg.

The significance for human nutrition of the sulfur-containing amino acid content of soy protein products has also been examined. It has been concluded that, for young children and adults, methionine supplementation of products containing soy protein products is not necessary; nor is methionine supplementation of the soy protein products themselves necessary for an adult diet, as was previously mentioned.

More specifically, in studies with children in the critical age period of 2 to 4 years, commercial soy protein isolates were shown to have 80% to 100% of the protein nutritional value of milk protein. The studies also indicated that these isolates were of high nutritional quality when they were the sole source of dietary protein (without amino acid fortification), using whole milk and whole egg as reference proteins. This was so even at levels lower than those recommended for this age group by FAO/WHO.

Amino acid, vitamin and mineral fortification of soy protein products is both feasible and nutritionally sound. Special fortification offers an opportunity to provide highly nutritional meals that would otherwise not be available for reasons of cost, stability, ease of preparation, or medical consideration (e.g., hypoallergenic infant formulations). Therefore, soy protein products offer opportunities for special formulas for geriatric, infant, hospital and postoperative feeding.

Some investigators have focused on the specific impact of increased soy consumption on human nutrition. They have concluded that, while phytic acid content appears to inhibit zinc availability, the situation is more complex and may involve other components. The combination of dietary phytate and a high calcium intake may have a greater impact on the availability of trace minerals, such as iron and zinc, than phytate in combination with lower dietary calcium levels. Hence, the total diet must be considered in assessing the nutritional significance of phytate content of food and its relationship to mineral availability.

In human studies, ingestion of soy concentrate at a level equivalent to about 23 grams of protein a day did not result in any unfavorable trends in calcium, magnesium, zinc or iron assimilation.

There is ample evidence that soy protein products have a positive influence on health. Recent studies have considered the total diet as a basis for explaining, at least in part, the differences in mortality rates from coronary artery disease, stroke, and several types of cancer in various countries.

Increasing evidence suggests that soy consumption and/or soy isoflavones might protect against various cancers and against other chronic diseases such as osteoporosis and cardiovascular disorders. Recent studies on animal models of mammary carcinogenesis identified the soybean isoflavone genistein as a chemopreventive agent.

Breast cancer, the second most common form of cancer in the West, occurs significantly less often in Asia and the Third World. Among women 60 to 65 years old, the rates of breast cancer are 199.4 per 100,000 in England and Wales, but only 52.3 per 100,000 in Japan. Epidemiologically, susceptibility to breast cancer is probably the result of environmental factors rather than genetic factors, with diet playing a major role. There are many vegetable sources of dietary estrogen, and several plants contain high levels of isoflavones (nonsteroidal estrogen), which have partial estrogen agonist-antagonist effects. Animal studies have shown dose-dependent reductions in chemically induced mammary tumor growth. All soy-derived foods contain isoflavones, which the Japanese consume at the rate of 150 to 200 mg/day. The most common forms of soy protein are beans, miso (a fermented soy product), tofu, and soy milk.

Daily ingestion of soy protein produces significant biological changes in women. Since the mitotic rate for breast tissue is four times as great during the luteal phase as during the follicular phase, a significant lengthening of the menstrual cycle, especially the follicular phase, may protect against breast cancer. (It should be noted that Asian women have longer menstrual cycles than western women.) Dietary soy protein may, in the future, provide an alternative approach to breast cancer prevention.

When estrogen production stops with menopause, women can experience high cholesterol and blood pressure, and they lose more bone at a faster rate. Estrogen replacement therapy addresses these problems but increases the risk of cancer. Soy protein, which contains isoflavones, has been shown to lower blood fats. We wanted to know whether soy isoflavones, which are weak estrogens, could combat these problems. We gave six postmenopausal women soy isoflavones for 6 weeks and found that the isoflavones appeared to alleviate those three problems. We intend to do larger studies to confirm these positive indications.

Soy protein products are also an excellent source of dietary fiber. Since dietary fiber seems to play a role in controlling blood cholesterol, and may have an effect in preventing colon cancer and improving glucose tolerance, studies with diets containing soy flour, soy concentrate or soy fiber merit special attention.

Diets low in dietary fiber have been correlated with increased incidence of colon cancer, coronary heart disease, diabetes, diverticular disease of the colon, and various other maladies of the lower gastrointestinal tract in man.

Few studies have dealt directly with the nutritional effects of soybean fiber in man. However, there is little argument that dietary fibers have a much greater effect on human nutrition than was previously realized.

Obesity is a genuine health concern in the minds of an informed populace. Soy protein products can make a significant contribution in weight reduction, mainly by providing essential high-quality protein in a concentrated form for specially designed, low-calorie/high-nutrient density meals.

Numerous dietary factors may favor an increased incidence of coronary heart disease (CHD). Animal fat is the most widely recognized atherogenic factor in the diet. A direct correlation has been established between saturated fatty acids, cholesterol levels, hypercholesterolemia, and the development of CHD.

On October 26, 1999, the FDA authorized use of health claims about the role of soy protein in reducing the risk of coronary heart disease on labeling of foods containing soy protein. This final rule is based on the FDA's conclusion that foods containing soy protein included in a diet low in saturated fat and cholesterol may reduce the risk of CHD by lowering blood cholesterol levels.

Coronary heart disease, one of the most common and serious forms of cardiovascular disease, is a major public health concern because it causes more deaths in the U.S. than any other disease. Risk factors for CHD include high total cholesterol levels and high levels of low density lipoprotein (LDL) cholesterol.

This new health claim is based on evidence that including soy protein in a diet low in saturated fat and cholesterol may also help to reduce the risk of CHD. Recent clinical trials have shown that consumption of soy protein compared to other proteins such as those from milk or meat, can lower total and LDL-cholesterol levels.

Foods that may be eligible for the health claim include soy beverages, tofu, tempeh, soy-based meat alternatives, and possibly some baked goods. Foods that carry the claim must also meet the requirements for low fat, low saturated fat, and low cholesterol content except the foods made with the whole soybean may also qualify for the health claim if they contain no fat in addition to that present in the whole soybean.

Until recent years, there have been few experimental and clinical studies on proteins from vegetable sources. This is due possibly to the higher interest in the 'dietary lipids' theory of atherosclerosis, and to the difficulties in selectively analyzing the role of dietary proteins, excluding such factors as fat and carbohydrates. Lately, however, substitution of animal proteins with soy proteins in the diets of some animals and humans has been studied with interest, primarily for its effect on blood lipids.

Epidemiological data on the effects of various diets on atherosclerosis and CHD development show, in fact, that vegetable protein intake is negatively correlated with plasma cholesterol and CHD development.

More recent clinical studies, in which soy protein isolate was substituted for animal proteins in the diet, have confirmed these findings. The value of soy protein isolate for producing significant reduction in total serum cholesterol, LDL- cholesterol, VLDL-cholesterol, and total serum triglycerides was well demonstrated, especially in hyperlipidemic subjects.

The effects of dietary protein on plasma cholesterol concentrations are well documented: animal proteins (casein) are hypercholesterolemic compared with plant proteins (soy protein). Although this effect of protein source on plasma cholesterol has been shown in many species, the mechanism is not completely understood. Some suggest that when soy protein is fed, cholesterol absorption and/or bile acid reabsorption is impaired. Others propose that changes in endocrine status, such as alteration in insulin:glucagon ratio and thyroid hormone concentrations, are responsible. The metabolic changes that have been observed on soy protein feeding in a variety of animal models, and in some cases humans, include increased cholesterol synthesis, increased bile acid synthesis (or fecal bile acid excretion), increased apolipoprotein B or E receptor activity and decreased hepatic lipoprotein secretion and cholesterol content, which are associated with an increased clearance of cholesterol from the blood. One hypothesis suggests amino acid composition or proportionality of soy causes changes in cholesterol metabolism (possibly via the endocrine system). Others have proposed that nonprotein components (such as saponins, fiber, phytic acid, minerals and the isoflavones) associated with soy protein affect cholesterol metabolism either directly or indirectly.

Projections indicate that the area of diet and health will continue to increase in importance. In this climate of public interest in nutrition, soy protein will receive attention as a highly nutritious, functional, and economical food ingredient.

See also: Soy

  • Soy Protein Council, 1255 Twenty-Third Street, NW, Washington, DC 20037
  • Scrimshaw, N.S., and Young, V.R., in "Soy Protein and Human Nutrition," p. 121, ed. by Wilcke, H.L., Hopkins, D.T., and Waggle, D.H. New York: Academic Press, 1979.
  • Torun, B., Pineda, O., Viteri, F.E., and Arroyave, G., in "Protein Quality in Humans: Assessment and In-Vitro Estimation," p. 374, ed. by Bodwell, C.E., Adkins, J.S., and Hopkins D.T. Westport: AVI Publ. Co., 1981.
  • Seely, S., Freed, D.L.J., Silverstone, G.A., Rippere, V., "Diet-Related Diseases: The Modern Epidemic" Westport: AVI Publ. Co., 1985.
  • Constantinou, A.l., Krygier, A., Mehta, R.R., and Murley, J.S., Induction of maturation of breast cancer cells by genistein. Universityof Illinois at Chicago, College of Medicine, Department of Surgical Oncology
  • Cassidy A et al. Soy Protein May Protect Against Breast Cancer. Am J Clin Nutr. 1994; 60: 333-40.
  • Wong William W. Effects Of Soy Protein And Soy Isoflavones On Blood Lipids, Blood Pressure, And Biochemical Markers Of Bone Metabolism In Postmenopausal Women. USDA/ARS Children's Nutr
  • Gibney, M.J., and Kritchevsky, D., "Animal and Vegetable Proteins in Lipid Metabolism and Atherosclerosis: Current Topics in Nutrition and Disease" New York: Alan R. Liss, Inc., 1983.
  • FDA APPROVES NEW HEALTH CLAIM FOR SOY PROTEIN AND CORONARY HEART DISEASE. FDA TALK PAPER. T99-48. Oct 20 1999
  • Ralston Purina Company, Protein Div., " A Review of Animal and Clinical Studies on the Effects of Isolated Soy Protein on Blood Lipids," 1985.
  • Forsythe WA. Overview of proposed mechanisms for the hypocholesterolemic effect of soy. Journal of Nutrition (USA), 1995, 125/3 SUPPL.

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