Joy of Soy

SUMMARY

  • Diabetes: Soybeans are low in carbohydrates and have a low glycemic index. Foods with a low glycemic index don’t cause a rapid increase in blood sugar levels when consumed. Thus making soybeans a good source of nutrition for people with diabetes.
  • Heart Disease: Soy has been shown to reduce LDL (bad) cholesterol, which is one of the most important factors in the prevention and treatment of coronary heart disease. Consuming 25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol may help also help to reduce the risk of heart disease.
  • Osteoporosis: Soy isoflavones help to protect against the decrease in bone density associated with age.
  • Cancer: Populations that regularly consume soy have a lower incidence of hormone related cancers such as breast and prostate cancer. This is attributed to the antioxidant characteristics found in soy isoflavones which protects against damage to cells.
  • Hormone Replacement Alternative: Soy phytoestrogens have been shown to reduce the symptoms of menopause.

THE SOYBEAN

Legumes have played an important role in the traditional diets of many regions throughout the world.1 The soybean is of particular interest due to its wide range of application and functionality. Soybeans are valued for their nutritional benefits and are known for their replacement in dairy foods as an alternative for people suffering from a dairy allergy and/or lactose intolerance. Soybeans also have a growing role in other areas, such as pharmaceutical and industrial applications (see Figure 1 for Soy Applications).2 Researchers continue to investigate the influence soy has on health and the role of soy in preventing or treating chronic diseases. The relationship between the dietary intake of soy and the low incidence of disease in Asian cultures compared to the United States, specifically hormone-dependant cancers, coronary heart disease and osteoporosis, suggests that the benefits of soy may extend well beyond the nutritional benefits it offers.3

Soybeans are a nutrient rich food.

  • CARBOHYDRATE: Soybeans are low in carbohydrates. They also have a low-glycemic index. This prevents over secretion of insulin which causes the unwanted effect of storing extra sugar in your blood stream. Stable blood sugar and insulin levels mean fewer hunger cravings and fewer calories being stored as fat.4
  • FAT: Soybeans are cholesterol free and low in fat, primarily comprised of unsaturated fats. This makes the soybean a great alternative in comparison to its counterparts - eggs, meat and dairy- which are high in saturated fat and cholesterol.
  • FIBER: Soybeans are a source of dietary fiber. The dietary guidelines set by the Food and Drug Administration (FDA) recommend consuming 25g of fiber per day (based on a 2,000 calorie diet).5 (Link to Fit With Fiber section.)
  • PROTEIN: Soybeans are high in protein and a source of “essential” amino acids. Amino acids are the building blocks of proteins, but not all amino acids can be produced by our bodies. Those amino acids that cannot be produced by our bodies are termed “essential” amino acids and must be obtained from the diet. While soybeans alone do not have an ideal balance of amino acids like that found in meat, they do provide some amount of each of the “essential” amino acids. Amino acids in whole grains combine well with amino acids in soy and legumes for a more ideal balance of amino acids.6
  • OTHER NUTRIENTS: Soybeans also provide important nutrients such as B-vitamins, folic acid, potassium, zinc and iron. The amount of these nutrients varies depending on the type of soy food.
  • PHYTONUTRIENTS: Phytonutrients are substances produced naturally by plants to protect themselves from disease. Isoflavones are one group of phytonutrients found in soybeans and are classified as phytoestrogens.6 Phytoestrogens are natural estrogens which mimic human estrogen but are 500-1000 times less potent.7 Soybeans are essentially the only natural dietary source of isoflavones available, to include daidzein, glycetein, and genistein. Isoflavones behave like antioxidants helping protect against cell damage and thus helping to protect against disease.8 Researchers continue to study the benefits of isoflavones and how they beneficially effects our health. (See Health Benefits section below for more information.)

HEALTH BENEFITS

Research has shown, aside from the nutritional aspects of soy, it also has a positive effect in helping to prevent and protect against certain diseases, specifically heart disease, osteoporosis, and hormone-dependant cancers such as breast and prostate cancers.

  • HEART DISEASE: Research has shown that soy protein helps to reduce cholesterol by lowering the levels of fat in the blood and reducing LDL (bad) cholesterol while raising the HDL (good) cholesterol.9 While there are many factors associated with coronary heart disease the reduction of elevated LDL cholesterol levels is one of the most important factors in the prevention and treatment of coronary heart disease. The isoflavones found in soy have also been shown to inhibit the growth of cells that form artery clogging plaque and work to escort cholesterol out of the body. The cholesterol reducing effects of soy are the most scientifically proven benefit.9 The amount of soy protein associated with reducing the risk of coronary heart disease is 25 grams or more of soy protein per day. The FDA has approved the health claim stating diets that are low in saturated fat and cholesterol and that include soy protein may reduce the risk of heart disease.2
  • OSTEOPOROSIS: Osteoporosis is a bone disease characterized by a loss in bone density. It is strongly associated with age and the decline in estrogen affecting primarily older, post-menopausal women, although older men are also at risk.10 Isoflavones, genistein and daidzein, not only help to prevent bone loss but have shown to increase bone density as well. Short term studies have shown isoflavones possess powerful bone building characteristics that inhibit the activity of cells (osteoclasts) which are responsible for breaking down bone, while stimulating the activity of cells (osteoplasts) which build up bone.11 Clinical data suggests that 80mg of isoflavones per day are needed to receive the benefits related to bone health.12
  • CANCER: Breast Cancer and Prostate Cancer: Researchers continue to investigate the influence soy has on health and the role of soy in preventing or treating hormone-dependant cancers. The long time presence of soy in Asian diets and the comparatively low rate of disease they experience -including breast and prostate cancers- suggests that soy may help to prevent cancer.3 It appears the phytoestrogens in soy may be responsible for these protective effects in that they inhibit the growth of cancer cells by binding to estrogen receptor sites on cells, blocking potent estrogen from linking up and affecting cell turnover rates. This diminishes the possibility of mutations that can lead to cancer in estrogen responsive tissues by lowering cell turnover rates.7 The most potent isoflavone, genistein, has been shown to inhibit certain enzymes necessary for tumor growth and reduce blood supply to tumors.13
  • HORMONE REPLACEMENT ALTERNATIVE: Isoflavones at the estrogen receptor site produce mild estrogenic effects enough to potentially reduce the symptoms of menopause.7 Studies have shown that traditional hormone replacement therapy (HRT) increases the risk of cancer, mainly breast cancer. The possibility that soy might exert the same advantages of estrogen, especially in regard to coronary heart disease and osteoporosis, but without the disadvantages, has led many to view soy as a natural alternative to conventional HRT.14 While there is growing interest in the role soy might play in treating menopausal symptoms, more research must be done before this relationship is more clearly understood.

So how much soy should an individual consume on a daily basis? The FDA states that 25 grams of soy protein per day, with a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. Products which carry this claim must provide 6.25g of soy protein per serving.2 However, in terms of the amount of soy isoflavones one should consumer there is insufficient evidence as to what form or amount is necessary to have a positive influence on health. Above all, moderation and a balanced diet are most important in maintaining a healthy lifestyle.

REFERENCES:

1. Messina, Mark J., “Legumes and soybeans: overview of their nutritional profiles and health effects.American Journal of Clinical Nutrition. 70.3 (1999): 439S-450S. 14 Mar. 2005.

2. Endres, Joseph G., Soy Protein Products: Characteristics, Nutritional Aspects and Utilization. Illinois: AOCS Press, 2001.

3. Gettingwell.com. PDR Health. 28 Jan. 2005.

4. Tabor, Aaron MD. “Soy Protein Reduces Feelings Of Hunger to Help You Lose Weight”. Theconservativevoice.com. The Conservative Voice. 15 Jan 2005.

5. “Guide to Nutrition Labeling Education Act and Requirements.FDA.gov. U.S. Food and Drug Administration. 15 Feb. 2005.

6. “Benefits of Soy Products.” Soy Info Online. 17 Mar. 2005.

7. Paxton, Suzanne (R.Ph.). “Soy Protein: Your Key To Better Health”. Soybean.com. 28 Jan. 2005.

8. VIPSoybeans.org. Varietal Information Program for Soybeans. 17 Mar. 2005.

9. Askdrsears.com. Ask Dr. Sears. 17 Mar. 2005.

10. Setchell and Lydeking-Olsen. “Dietary phytoestrogens and their effect on bone: evidence from in vitro and in vivo, human observational, and dietary intervention studies.American Journal of Clinical Nutrition. 78.3 (2003): 593S-609S. 18 Mar. 2005.

11. “The Influence of Isoflavones on Osteoporosis.Isoflavones.info. 18 Mar. 2005.

12. Messina M, Ho S, Alekel DL. “Skeletal benefits of soy isoflavones: a review of the clinical trial and epidemiologic data.” Curr Opin Clin Nutr Metab Care. 7.6 (2004): 649-658. National Center for Biotechnology Information. PubMed. 18 Mar. 2005. PMID:15534433

13. “Isoflavones and Cancer.Isoflavones.info. 18 Mar. 2005.

14. Messina and Loprinzi. “Soy for Breast Cancer Survivors: A Critical Review of Literature.The American Society for Nutritional Sciences. J. Nutr. 131.11 (2001): 3095S-3108S. 28 Jan 2005.