The effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomized placebo-controlled trials.

Key findings:

Despite increased research on flaxseed in the last decade, there are inconsistencies between trials examining its effects on body composition indices. Some trials suggest an inverse association between flaxseed consumption and body composition indices. Studies also show no reduction in body composition compared with control. This study performed a comprehensive systematic review and meta-analyses of available randomized controlled trials to assess the overall effects of flaxseed on body composition indices in adults. The key findings indicate that participants ingesting flaxseed products had lower body weight, BMI and waist circumference (WC) as after the intervention than controls. Subgroup analyses showed that body composition indices were reduced with whole flaxseed consumption only, in trials lasting ≥12 weeks, and among participants with BMI ≥ 27 kg/m. These findings may be explained by the subsequent increase in circulating ALA after flaxseed supplementation. It appears that individuals with higher BMI were more likely to be positively affected by the supplementation. The study also showed that the influence of flaxseed on BMI was more striking in women than in men; however, as three articles did not report the sex composition of the participants, the exact sex-specificity effect of flaxseed remains unclear.

Abstract

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.