The purpose of this study is to test the effect of 1 year of added dietary soy protein
and/or soy isoflavones on bone mineral density in late postmenopausal women.
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:
1. Does soy protein alone affect bone metabolism?
2. Do isoflavones, given with soy protein, affect bone metabolism?
3. 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.
- Postmenopausal women 65 years old or older
- Able to travel to the clinical sites for follow-up visits
- History of disease that may affect bone metabolism (including Paget's disease,
primary hyperparathyroidism, osteomalacia, untreated hyperthyroidism, or multiple
- 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
Jane Kerstetter, PhD
Department of Allied Health Sciences, University of Connecticut