Effects of extracted soy isoflavones alone on blood total and LDL cholesterol: Meta-analysis of randomized controlled trials

Abstract

When provided concurrently with soy protein for 1-3 months, soy isoflavones exert synergistic or additive cholesterol-lowering effects. This meta-analysis was performed to evaluate the effects of extracted soy isoflavones alone (not ingested concurrently with soy protein) on total and low density lipoprotein (LDL) cholesterol. MEDLINE (1966-2007), EMBASE (1966-2007), CENTRAL (1966-2007), ICHUSHI (1983-2008), and CNKI (1979-2007) were searched for randomized placebo-controlled trials published in English, Japanese, and Chinese, describing the changes in lipid profiles in adult humans resulting from ingestion of extracted soy isoflavones for 1-3 months. Reference lists of relevant systematic reviews and meta-analyses were hand-searched. Meta-analysis of 10 and 9 trials with usable information using REVMAN found that an average of 70 mg soy isoflavones/day (27-132 mg, as the aglycone form) alone had a nonsignificant effect on total (0.01 mmol/L [95% CI: -0.12, 0.14]; P = 0.86) and LDL (0.03 mmol/L [95% CI: -0.11, 0.16]; P = 0.71) cholesterol in menopausal women, respectively. It is concluded that ingestion of about 70 mg extracted soy isoflavones/day alone for 1-3 months does not improve total and LDL cholesterol levels in normocholesterolemic menopausal women; further studies are needed to verify the effects of extracted soy isoflavones.

Keywords: LDL cholesterol; extracted soy isoflavones; lipid; total cholesterol.

Figure 1

The QUOROM statement flow diagram. Notes: Potentially relevant randomized controlled trials (RCTs) were identified from database PubMed (n = 837), CENTRAL (n = 386), EMBASE (382), ICHUSHI (n = 62) and CNKI (n = 236). Abbreviations: QUOROM, quality of reports of meta-analyses of randomized controlled trials; RCTs, randomized controlled trials; TC, total cholesterol; LDL-C, low density lipoprotein cholesterol.

Figure 2

Effect of extracted soy isoflavones (ESI) alone on blood LDL cholesterol. Notes: Weight assigned by REVMAN software based on N and SD. WMD, Weighted mean difference in endpoint values between the ESI alone (not ingested concurrently with soy protein) and placebo groups; fixed, fixed effect model. Horizontal lines denote the 95% CI. ▪, point estimate (size of the square corresponds to its weight); ♦, combined overall effect of ESI treatment.