Dietary soy supplement on fibromyalgia symptoms: a randomized, double-blind, placebo-controlled, early phase trial

Abstract

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.

Figure 1

Flow chart of patients in the placebo-controlled soy supplement trial.

Figure 2

Total FIQ scores of patients in soy supplement trial, with intent-to-treat analysis (A–D) and per–protocol analysis (E–H). Score of patients randomly assigned to receive soy at study entry (A) and score of patients after 6 weeks of soy treatment (B). Score of patients randomly assigned to receive placebo at study entry (C) and score of patients after 6 weeks of placebo (D). Score of patients randomly assigned to receive soy at study entry (E) and score of patients after 6 weeks of soy treatment (F). Score of patients randomly assigned to receive placebo at study entry (G) and score of patients after 6 weeks of placebo (H).

Figure 3

CES-D scores of patients in soy supplement trial, with intent-to-treat analysis (A–D) and per-protocol analysis (E–H). Score of patients randomly assigned to receive soy at study entry (A) and score of patients after 6 weeks of soy treatment (B). Score of patients randomly assigned to receive placebo at study entry (C) and score of patients after 6 weeks of placebo (D). Score of patients randomly assigned to receive soy at study entry (E) and score of patients after 6 weeks of soy treatment (F). Score of patients randomly assigned to receive placebo at study entry (G) and score of patients after 6 weeks of placebo (H).