Soy isoflavones (diadzein, genistein, glycitein) are a family of plant-derived polyphenolic compounds with similar structure and properties to mammalian estrogen and possess weak estrogenic activity (phytoestrogens). Once ingested, gut microbiota biotransform the β -glucosides to their aglycone form (active form), which in turn could be further biotransformed to various metabolites, including equol. Interestingly, it has been observed that only approximately 30-40% of adults in Western populations have the ability to produce equol. We therefore propose that the inconsistencies in the current literature examining the effectiveness of soy as a lipid-lowering food may be explained by inter-individual variation in microbial biotransformation of soy isoflavones. Current literature examining the role of equol status on serum lipid reductions is inconclusive and has not yet been systematically reviewed.
To determine the effect of soy consumption on serum lipids based on equol status. Christina Paul proposes:
- To conduct a meta-analysis of randomized controlled trials to assess effect modification of the lipid-lowering effect of soy foods by equol status.
- To investigate heterogeneity in the pooled data with planned subgroup analyses and meta-regression techniques across patient catagories (healthy, type 1 and 2 diabetes, obese, hyperlipidemia, primary CVD, secondary CVD), isoflavone dose (diadzein, genistein, glycitein), food form (soy foods, soy protein supplements), and duration of follow-up.
- To undertake further subgroup analyses (gender, age, background, diet, BMI, etc.) and sensitivity analyses to explore heterogeneity identified during the primary pooled analysis.
- To disseminate the results of this meta-analysis at local, national, and international meetings and to promote the results among scientific, clinical, and industrial opinion leaders in nutrition.
- To use the results of this meta-analysis to inform general and heart healthy nutrition recommendations in dietetic practice and determine the direction of future clinical nutrition research.