Summary
Flaxseed consumption may be inversely associated with obesity; however, findings of available randomized controlled trials (RCTs) are conflicting. The present study aimed to systematically review and analyse RCTs assessing the effects of flaxseed consumption on body weight and body composition. PubMed, Medline via Ovid, SCOPUS, EMBASE and ISI Web of Sciences databases were searched up to November 2016. Mean changes in body composition indices including body weight, body mass index (BMI) and waist circumference were extracted. Effect sizes were expressed as weighted mean difference (WMD) and 95% confidence intervals (CI). Heterogeneity between studies was assessed with the I2 test. Publication bias and subgroup analyses were also performed. The quality of articles was assessed via the Jadad scale. A total of 45 RCTs were included. Meta‐analyses suggested a significant reduction in body weight (WMD: −0.99 kg, 95% CI: −1.67, −0.31, p = 0.004), BMI (WMD: −0.30 kg m−2, 95% CI: −0.53, −0.08, p = 0.008) and waist circumference (WMD: −0.80 cm, 95% CI: −1.40, −0.20, p = 0.008) following flaxseed supplementation. Subgroup analyses showed that using whole flaxseed in doses ≥30 g d−1, longer‐term interventions (≥12 weeks) and studies including participants with higher BMI (≥ 27 kg m−2) had positive effects on body composition. Whole flaxseed is a good choice for weight management particularly for weight reduction in overweight and obese participants.
Whole flaxseed, but not flaxseed oil and lignan extract, has significant effects on improving glycemic control. Further studies are needed to determine the benefits of flaxseed on glycemic parameters.
Promising experimental studies suggest that quercetin has potential anti-inflammatory effects. However, the results of current clinical trials on quercetin's effects on the C-reactive protein (CRP), a sensitive inflammatory biomarker, are ambiguous. We conducted a meta-analysis of available randomized controlled trials (RCTs) to resolve this inconsistency and quantify the net effect of quercetin on circulating CRP concentrations. A systematic search was performed in several databases including SCOPUS, PubMed-Medline and Google Scholar until 16 June 2016. We used a random-effects model in combination with weight mean difference (WMD) and 95% confidence intervals (CI) for data analysis. Standard methods were used for the assessment of heterogeneity, meta-regression, sensitivity analysis and publication bias. The meta-analysis of seven RCTs (10 treatment arms) showed a significant reduction of circulating CRP levels (WMD: -0.33 mg/l; 95% CI: -0.50 to -0.15; P<0.001) following quercetin supplementation. In the subgroup analysis, a significant reducing effect was observed in trials with ⩾500 mg/day dosage (WMD: -0.34 mg/l; 95% CI: -0.52, -0.16; P⩽0.001) and in those with CRP <3 mg/l (WMD: -0.34 mg/l; 95% CI: -0.51, -0.18; P⩽0.001). In meta-regression, there was no association between changes in CRP concentrations, dose of supplementation and CRP baseline values. Our findings showed a significant effect of quercetin supplementation on the C-reactive protein-especially at doses above 500 mg/day and in patients with CRP <3 mg/l.
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