Soy Protein and Quality of Life in Postmenopausal Women

  • Hormone Replacement Therapy (HRT)
  • Menopause
  • Soy (Glycine max)
  • Soy Protein
  • Date: May 31, 2005 HC# 050556-281

    Re: Soy Protein and Quality of Life in Postmenopausal Women

    Kok L, Kreijkamp-Kaspers S, Grobbee DE, Lampe JW, van der Schouw YT. A randomized, placebo-controlled trial on the effects of soy protein containing isoflavones on quality of life in postmenopausal women. Menopause. 2005;12(1):56-62.

    Women experience many age-related physical and psychological changes after menopause, many of which have been linked to declining estrogen levels.
    Examples of these changes include increased risk of bone fractures, a higher incidence of cardiovascular disease, sleep problems, mood changes, vasomotor symptoms, and overall decline in perceived quality of life. Hormone replacement therapy (HRT) has shown beneficial effects on quality of life parameters in clinical trials. However, there is growing concern about the possible harmful side effects of this intervention, including breast and endometrial cancer and venous thromboembolism (the blocking of a blood vessel by a particle that has broken away from a blood clot at its site of formation).

    Supplementation with plant-derived phytoestrogens provides women with an alternative to conventional HRT. The three main classes of phytoestrogen molecules, isoflavones, lignans, and coumestans, have a non-steroidal structure that resembles the hormone estradiol. Several studies have already shown beneficial effects on cardiovascular disease risk factors, bone mineral density and hot flashes when women receive phytoestrogen supplementation. Furthermore, these trials have shown no indication of an increased risk of breast or endometrial cancer. The current study endeavors to provide additional data about soy (Glycine max) protein supplementation by investigating its effects on quality of life (health status, life satisfaction and depression) in older postmenopausal women (60-75 years) on a long-term basis (one year).

    This double blind, randomized, placebo-controlled trial included 202 women and was conducted at the Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, The Netherlands. Subjects were screened and excluded if they had a history of liver disease, thromboembolism, carcinoma, used HRT within 6 months of enrollment, or an allergy to soy or milk protein. In addition, all subjects had an endometrial thickness of less then 4 mm and a normal mammogram within the year prior to commencement of the trial. Mammograms and endometrial thickness were monitored during the trial as safety precautions. The dropout rate was 24% (49 subjects) during the intervention period. Thirty-five of these 49 subjects stayed in the study for at least 1 month and participated in a final visit.
    The intervention supplement consisted of 25.6 g of a soy protein powder with a naturally occurring isoflavone content of 52 mg genistein, 41 mg daidzein, and 6 mg of glycitein (aglycone weights) (Solae brand soy protein, The Solae Company, St. Louis, MO). The authors state that the "total serving size of the product was 36.5 g." However, they do not mention what ingredients constituted the additional 10.9 g. The control group received 36.5 g per day of a milk protein powder that looked and tasted identical to the intervention supplement (DuPont Protein Technologies, St. Louis, MO). The subjects were required to take the supplements daily for 12 months, and they were permitted to mix the powders with food or beverages.

    Quality of life (health status, life satisfaction and depression) was evaluated at baseline and at the end of the intervention period through the use of three assessment tools:
    1) The SF-36 consists of a questionnaire (self-administered) containing 36 items that measure the subject's own perception of their health status in 8 categories, including physical problems, mental health, pain, and vitality.
    2) The QLSM consists of 3 modules that evaluate health and life satisfaction.
    3) The GDS is a screening instrument (self-rated) especially designed to assess depression in the elderly.

    There were no statistically significant effects observed between the intervention group and the placebo group in this study. The authors conclude, "The present study did not demonstrate an overall beneficial effect of a 1-year supplementation of soy protein containing naturally occurring isoflavones on quality of life in postmenopausal women."
    They point out 2 primary limitations of the study, which may have contributed to the negative result. The study population consisted of healthy women who rated their health status as "high" at baseline; expecting further improvement in such subjects may be unrealistic. In addition, the study population was older than the age group that typically suffers from climacteric symptoms. Studies that enroll women who are suffering from such symptoms are more likely to show an improvement in quality of life through symptom relief.

    Two other aspects of the study design bear mentioning. First, compliance was assured only through assessment of plasma genistein levels at the time of the final visit. Although there was a significant difference in blood levels between the two groups, it seems entirely possible that compliance may have been irregular in a study of this length. The second point regards the authors' stated intention "to assess the effects of soy protein…on bone, vascular aging, cognitive function, quality of life (Qol), and physical performance." There was, in fact, no testing performed or objective data collected for any of these parameters. Such data might have shown physiological changes that were not revealed on the subjective questionnaires.

    -Cathleen Rapp, N.D.

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