Numerous studies have indicated that low levels of serum adiponectin are linked with the development of various chronic diseases. While some recent research has suggested that soy has a positive impact on serum adiponectin levels, the results are inconsistent. Therefore, we aim to conduct a thorough systematic review and meta-analysis of randomized controlled trials (RCTs) that investigate the effects of soy on serum adiponectin levels in adults. The search was conducted until March 2024 on PubMed, Scopus, Web of Science, and Cochrane Library databases to identify RCTs that studied the effects of soy supplementation on serum adiponectin levels. A random-effects model was used to pool the weighted mean differences (WMDs). Ten and nine RCTs were selected for the systematic review and meta-analysis, respectively. After analyzing data from 9 eligible RCTs, it was found that soy supplementation did not significantly impact the concentrations of adiponectin (WMD = −0.24 μg/mL; 95% confidence interval, −1.56 to 1.09; p = 0.72). However, there was significant heterogeneity between the studies (I2 = 89.8%, p < 0.001). Sensitivity analysis showed that overall estimates were not affected by the elimination of any study. We did not observe any evidence regarding publication bias. In conclusion, soy supplementation did not have a significant effect on adiponectin levels in adults. However, further RCTs are needed with longer intervention duration, higher doses, and studies conducted in different countries.
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Rheumatoid arthritis (RA) is a systemic inflammatory autoimmune disorder with widespread synovitis. Isoflavones, the main active component of soy, have been reported to have potent anti-inflammatory effects; the previous RA animal models showed the promising effect of soy supplementation. We aimed to evaluate the effect of soy bread on inflammatory markers and lipid profiles in RA patients. The present study was designed as a randomized controlled trial. RA patients were randomly allocated to obtain soy bread (n = 22) or placebo bread (n = 22) for 8 weeks. Fasting serum levels of lipid profile, total antioxidant capacity (TAC), tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), and DAS28 were checked. Findings showed that there were no significant differences between the two groups in physical activity and dietary intake at the beginning of the study and the end of the study. There were no significant differences between the two groups in measured lipid profile markers, including high-density lipoprotein, low-density lipoprotein, total cholesterol, triglyceride, and very low-density lipoprotein, at the end of the trial. In addition, TAC and CRP also were not significant at the end of the trial between the 2 groups (0.66 and 0.12, respectively). However, the serum levels of TNF-α reduced significantly in the soy bread group at the end of the intervention (p < 0.000) and compared with the control group (p < 0.019). Soy bread consumption only decreased circulating TNF-α serum concentration. Other outcome measures were not changed following supplementation. Future long-term, well-designed studies are needed to confirm these findings.
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