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Evidence-Based Complementary and Alternative Medicine
Volume 2011, Article ID 350697, 6 pages
Original Article

Dietary Soy Supplement on Fibromyalgia Symptoms: A Randomized, Double-Blind, Placebo-Controlled, Early Phase Trial

1Division of General Internal Medicine, Mayo Clinic, Rochester, MN, USA
2The Fibromyalgia Treatment Program, Mayo Clinic, Rochester, MN, USA
3The Fibromyalgia Treatment/Rehabilitation Center, Mayo Clinic, Rochester, MN, USA
4The Division of Biostatistics, Mayo Clinic, Rochester, MN, USA
5The Division of Tertiary Psychiatry and Psychology, Mayo Clinic, Rochester, MN, USA

Received 25 November 2008; Accepted 28 May 2009

Copyright © 2011 Dietlind L. Wahner-Roedler et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Most patients with fibromyalgia use complementary and alternative medicine (CAM). Properly designed controlled trials are necessary to assess the effectiveness of these practices. This study was a randomized, double-blind, placebo-controlled, early phase trial. Fifty patients seen at a fibromyalgia outpatient treatment program were randomly assigned to a daily soy or placebo (casein) shake. Outcome measures were scores of the Fibromyalgia Impact Questionnaire (FIQ) and the Center for Epidemiologic Studies Depression Scale (CES-D) at baseline and after 6 weeks of intervention. Analysis was with standard statistics based on the null hypothesis, and separation test for early phase CAM comparative trials. Twenty-eight patients completed the study. Use of standard statistics with intent-to-treat analysis showed that total FIQ scores decreased by 14% in the soy group (P = .02) and by 18% in the placebo group (P < .001). The difference in change in scores between the groups was not significant (P = .16). With the same analysis, CES-D scores decreased in the soy group by 16% (P = .004) and in the placebo group by 15% (P = .05). The change in scores was similar in the groups (P = .83). Results of statistical analysis using the separation test and intent-to-treat analysis revealed no benefit of soy compared with placebo. Shakes that contain soy and shakes that contain casein, when combined with a multidisciplinary fibromyalgia treatment program, provide a decrease in fibromyalgia symptoms. Separation between the effects of soy and casein (control) shakes did not favor the intervention. Therefore, large-sample studies using soy for patients with fibromyalgia are probably not indicated.