Soy and Human Health

• The Astonishing Functional Food: Soy Protein and Soy Constituents
• Soy Protein and Coronary Heart Disease
• Soy and Digestive Tract Health
• Soy Foods in Chronic Renal Disease
• How Can Soy Help Diabetes?
• Soy Protein Enhances Energy, Stamina and Sport Performance
• Soy and Cancers
• Soy and Breast Cancer
• Soy and Menopausal Symptoms
• Soy and Pre-Menstrual Syndromes
• Soy and Bone Health
• Losing Weight Healthily with Soy
• Soy and Urological Cancer
• Soy Lecithin and Human Health
• Clinical Abstracts on Soy
• Soy Clinical Reviews in Reputable Medical Journals: 1995-2002

Soy and Bone Health

Human studies showed a bone-sparing effect of soy protein with isoflavones at 80-90 mg/d. In a recent study conducted was to evaluate the effect of 2 y of consumption of isoflavone-rich soymilk (100 mg/d), natural transdermal progesterone (25 mg/d), or both on bone mineral density in the lumbar spine and hip. Postmenopausal Caucasian women, mean age 58 y (range 41-75 y), were randomly assigned, double-blind, to one of four treatment-groups: isoflavone-rich soymilk (soy+, n = 23), transdermal progesterone (TPD+, n = 22), both (soy+, TDP+, n = 22), or placebo (isoflavone-poor soymilk, soy-) and progesterone-free cream (TDP-, n = 22). At baseline, 1 y, and 2 y bone mineral content (BMC) and density (BMD) were measured in lumbar spine and hip by using dualenergy x-ray absorptiometry. All participants received a broad-spectrum food supplement (Osforte®) containing 680 mg calcium (citrate and carbonate), 300 mg magnesium (aminochelate), 20 mg silicium (sodium metasilicate), 15 mg zinc (aminochelate), 6 mg manganese (aminochelate), 3 mg boron (proteinate), 2 mg copper (aminochelate), 200 mg vitamin C, 40 mg pyridoxine, 200 IU vitamin D3, and 1 mg vitamin K1. The soymilk was enriched with calcium to 120 mg/100 mL; with a daily intake of 400-500 mL, total calcium intake from diet, soymilk, and food supplement was 1200-1500 mg/d. Of 107 women entering the study, 7 withdrew early, 6 developed intolerance to soy, and 2 developed intolerance to the skin cream. Three were excluded from analysis because of self-reported poor compliance, leaving 89 for analysis, 22-23 per group. The percentage change in lumbar spine BMD and BMC respectively, did not differ from zero in the soy+ group (+1.1%, +2.0%) and TDP+ group (-1.1%, +0.4%) but loss occurred in the soy- group (+4.2%, P = <0.01; +4.3%, P = <0.01) and the soy+, TDP+ group (+2.8%, P = 0.01; +2.4%, P = 0.05). No significant changes occurred in any group for femoral neck BMD or BMC, indicating that the food supplement, soy protein, or both had a stabilizing effect across the groups. It was concluded that Isoflavone-rich soymilk prevented bone loss in the lumbar spine and transdermal progesterone had a bone-sparing effect in postmenopausal women. The combined treatment however, showed a negative interaction, resulting in bone loss to a greater extent than with either treatment alone but less pronounced than placebo.

Several lines of evidence suggest that soy isoflavones and related compounds act as estrogen agonists and have beneficial skeletal effects. However, little is known about the metabolic effects of isoflavones and, specifically, about their effects on calcium handling by the body. Fifteen postmenopausal women were studied under three different 1-mo controlled dietary interventions in a randomized, crossover design: soy protein enriched with isoflavones (SP), soy protein void of isoflavones (SM), and a casein-whey (CW) control. Dietary calcium was 1106 mg/d and dietary isoflavones were ±65 mg/d. A combination of metabolic balance methodology and radioisotopic tracer techniques were used to measure calcium absorption, calcium excretion, and net calcium retention. Fractional calcium absorption of 0.20 ± 0.05 (SP), 0.20 ± 0.04 (SM), and 0.19 ± 0.06 (CW) was not affected by dietary treatment. Urinary calcium excretion was significantly reduced (P <0.05) with the consumption of soy compared with casein whey: SP, 81 ± 32 mg (2.0 ± 0.8 mmol); SM, 81 ± 42 mg (2.0 ± 1.1 mmol); and CW, 121 ± 69 mg (3.0 ± 1.7 mmol). Net calcium retention was significantly increased (P <0.01) with the consumption of soy compared with casein whey: SP, 3 ± 50 mg (0.08 ± 1.3 mmol); SM, 16 ± 61 mg (0.4 ± 1.5 mmol); and CW, -50 ± 89 mg (-1.3 ± 2.2 mmol). Thus, soy protein, but not isoflavones, reduced urinary calcium excretion and enhanced net calcium retention compared with milk protein. However, neither soy protein nor isoflavones influenced fractional calcium absorption.