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ARS Home » Plains Area » Grand Forks, North Dakota » Grand Forks Human Nutrition Research Center » Healthy Body Weight Research » Research » Publications at this Location » Publication #159105

Title: CONTROLLED SUBSTITUTION OF SOY PROTEIN FOR MEAT PROTEIN: EFFECTS ON CALCIUM RETENTION, BONE, AND CARDIOVASCULAR HEALTH INDICES IN POSTMENOPAUSAL WOMEN

Author
item ROUGHEAD, ZAMZAM
item HUNT, JANET
item JOHNSON, LUANN - UNIV OF ND
item BADGER, THOMAS - UNIV OF ARKANSAS
item LYKKEN, GLENN - UNIV OF ND

Submitted to: Journal of Clinical Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2004
Publication Date: 1/1/2005
Citation: Roughead, Z.K., Hunt, J.R., Johnson, L.K., Badger, T.M., Lykken, G.I. 2005. Controlled substitution of soy protein for meat protein: effects on calcium retention, bone, and cardiovascular health indices in postmenopausal women. Journal of Clinical Endocrinology and Metabolism. 90(1):181-9.

Interpretive Summary: Meat intake is often cited as a risk factor for the development of osteoporosis while intake of plant proteins (such as soy) is thought to protect against bone loss. However, to date, a careful comparison of how these two proteins affect handling of calcium in the body has not been made. In this feeding study, thirteen healthy postmenopausal women ate diets which had similar calcium content (~ 700mg), but in which 25g of soy protein with high amounts of isoflavones were substituted for the same amount of meat protein in random order. Isoflavones are thought to be the component in soy which offers beneficial effects on bone health. After 3 weeks of equilibration on each diet, we monitored the retention of a calcium tracer for 28 days by using a sensitive method called whole body scintillation counting. We also measured indicators of bone metabolism in urine and blood samples from the subjects. We found that the urinary acidity was about 20% lower when the women were eating the soy diet, however, the amount of calcium retained in the body was the same (14% on both diets). Also, these diets did not affect the amount of calcium lost in the urine or any of the indicators of bone metabolism. Additionally, serum cholesterol and homocysteine did not change during either diet. We have concluded that substituting 25g of soy protein for meat protein does not change how the body handles calcium in postmenopausal women.

Technical Abstract: Background: The effect of animal versus plant protein intake on calcium retention and bone metabolism is not known. Objectives: The primary objective was to determine the effects of substituting 25g of soy protein for meat protein on calcium retention and bone biomarkers. The secondary objective was to determine the dietary effects on serum homocysteine and lipid profile. Design: Healthy postmenopausal women (n=13) ate diets with similar calcium content (~700 mg/d), in which 25g of high isoflavone-containing soy protein (SOY) was substituted for an equivalent amount of meat protein (CONTROL) for 7 wk each, separated by 2 wk, in a randomized crossover design. After 4 wk of equilibration, calcium retention was measured by extrinsically labeling the 2-d menu with 47Ca, followed by whole body counting for 28 d. Urinary calcium and indicators of renal acid excretion were measured at wk 3, 5 and 7. Biomarkers of bone and cardiovascular health were measured at the beginning and end of each dietary period. Results: Calcium retention was similar during the CONTROL and SOY diets (d 28, % dose, mean ± pooled SD: 14.1 and 14.0 ± 1.6, respectively). Despite a 15-20% lower renal net acid excretion during the SOY diet, urinary calcium loss was unaffected by diet. Diet did not affect any of the measured indicators of bone or cardiovascular health. Conclusions: A daily consumption of plant protein (as high isoflavone-soy protein) in place of animal protein (as meat) for several wk, in a diet typical for postmenopausal women, reduced renal net acid excretion, but did not affect calcium retention, or indicators of bone and cardiovascular health.