Systematic review and meta-analysis support flaxseed consumption for weight loss

Over the last decade there has been an increased interest in the role of flaxseed and body weight. Flaxseed contains lignans, a-linolenic acid (ALA) and is a rich source of dietary fibre, including both insoluble and soluble fibre. These compounds have been associated with weight reduction (1). However, there are inconsistencies between trials examining the effects of flaxseed on body composition indices. Some trials suggest an inverse association between flaxseed consumption and weight reduction. Studies also show no changes compared with control. A new publication performed a comprehensive systematic review and meta-analyses of available randomized controlled trials (RCTs) to assess the overall effects of flaxseed on body composition indices in adults (2). 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 (WC) were assessed. Following application of the exclusion criteria, 45 eligible RCTs with 49 treatment arms were included in the meta-analysis. Of these, 28 articles reported effects of flaxseed on weight, 35 articles on BMI, and 13 articles on WC.

The key findings indicate that participants ingesting flaxseed (>30g/day) had lower body weight, BMI and WC 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.

The authors indicate that the findings may be explained by the subsequent increase in circulating ALA after flaxseed supplementation. Obesity is recognized as a state of low-grade, chronic inflammation. ALA may protect against inflammation through its effects on eicosanoid metabolism. Eicosanoids are hormone-like substances that affect inflammation and can be produced from both ALA (anti-inflammatory) and LA (mostly pro-inflammatory). The typical Western diet is high in LA and low in ALA. This ratio can be shifted to guard against inflammation by increasing dietary ALA intake from flaxseed (3).

Flaxseed provides 16% of the recommended daily intake for fibre in a 2 tablespoon serving. Fibre, particularly soluble fibre, may help to promote weight loss or prevent weight gain by absorbing large quantities of water to induce a feeling of fullness and delay gastric emptying (4). Supplements providing 2.5 g of flaxseed soluble fibre in a beverage or tablet form significantly reduced energy intake compared to control (702 vs. 768 kcal). Subjective measures of satiety and fullness increased, while hunger and prospective food intake decreased (5). Together these studies provide support for the role of flaxseed fibre in appetite and weight reduction.

This meta-analysis suggests 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 profound 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. Whole flaxseed is a good choice for weight management particularly for weight reduction in overweight and obese participants. This study plus others can be reviewed in the ‘weight’ category of flaxresearch.com.

References

  1. https://www.healthyflax.org/quadrant/media/files/pdf/HEAL.factsheet_DIABETES.pdf
  2. Mohammadi-Sartang M, Mazloom Z, Raeisi-Dehkordi H, et al. The effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomized placebo-controlled trials. Obes Rev. 2017 Jun 21. doi: 10.1111/obr.12550.
  3. Caligiuri SP, Aukema HM, Ravandi A, Pierce GN. Elevated levels of pro-inflammatory oxylipins in older subjects are normalized by flaxseed consumption. Exp Gerontol. 2014 Nov;59:51-7. doi: 10.1016/j.exger.2014.04.005.
  4. Kristensen M, Jensen MG. Dietary fibres in the regulation of appetite and food intake. Importance of viscosity. Appetite. 2011 Feb;56(1):65-70. doi: 10.1016/j.appet.2010.11.147.
  5. Ibrügger S, Kristensen M, Mikkelsen MS, Astrup A. Flaxseed dietary fiber supplements for suppression of appetite and food intake. Appetite. 2012 Apr;58(2):490-5. doi: 10.1016/j.appet.2011.12.024.