Soy and Isoflavones Effect on Bone

Although soy foods contain several components (isoflavones and amino acids) that could potentially have positive effects on bone health, there are few long term, large, clinical trials using soy as a means of improving bone mineral density. The objective of this study is to provide daily soy protein and isoflavones to healthy older women in order to answer three major questions:

• Does soy protein alone affect bone metabolism?
• Do isoflavones, given with soy protein, affect bone metabolism?
• What dose of isoflavones affects bone in older women?

We hypothesize that soy protein will have a beneficial effect on bone in older women compared to control protein. Further, we hypothesize that there will be an additional benefit to bone in women who receive soy protein plus isoflavones (at both doses) compared to soy protein alone.

Both control and soy proteins used in the study were isolates, meaning they were the highest concentration of protein (85-90% by weight) in order to minimize the volume of protein supplement that each woman was asked to ingest on a daily basis. The soy protein was an alcohol-washed, soy protein isolate containing 90% protein and negligible isoflavone (0.2 mg/g product). The control protein was a mix consisting of 50% protein from sodium caseinate, 25% protein from whey protein and 25% from egg white protein. The use of a mix of proteins as a control provides a more balanced level of amino acids, mimics the real life mix of proteins that humans typically consume, and avoids the unique characteristics of one source of protein. In order to maintain the dietary protein intake constant, the participant was counseled to decrease her intake of other sources of protein from primarily animal sources by approximately 3 ounces per day (the approximate equivalent of the protein powders). The isoflavones tablets each contained 57 mg of total isoflavone from primarily genistein, glycitein, and daidzein and their beta-glycosides.

Inclusion criteria

• Postmenopausal women 65 years old or older
• Able to travel to the clinical sites for follow-up visits

Exclusion criteria

• History of disease that may affect bone metabolism (including Paget's disease, primary hyperparathyroidism, osteomalacia, untreated hyperthyroidism, or multiple myeloma)
• Cancer of any kind (except basal or squamous cell of skin) in past 5 years
• Use of any of the following medications within the past 2 years: calcitonin, calcitriol, heparin, phenytoin, phenobarbital
• Use at any time of bisphosphonates, long-term corticosteroids (over 6 months), methotrexate, or fluoride
• Estimated creatinine clearance less than 50 ml/min
• History of chronic liver disease or evidence of liver disease on screening
• History of hip fracture
• Known vertebral fracture within the past year
• Vegans