Adults with overweight or obesity who consumed whole flaxseed for at least 12 weeks experienced reductions in body weight, BMI and waist circumference when compared with adults who consumed a placebo for the same period, according to a meta-analysis of 45 randomized controlled trials.
“Despite increased research on flaxseed in the last decade, there are inconsistencies between trials examining its effect on body composition indices,” Mohsen Mohammadi-Sartang, MSc, PhD, of the School of Nutrition and Food Sciences at Shiraz University of Medical Sciences, Iran, and colleagues wrote. “Some trials suggest an inverse association between flaxseed consumption and body composition indices, while others show no or little reduction in body composition compared with control[s] following flaxseed supplementation.”
Mohammadi-Sartang and colleagues analyzed data from 2,789 participants in 45 randomized controlled trials with 49 treatment arms that explored the influence of flaxseed or its products (whole or ground flaxseed, lignin supplement or flaxseed oil) on body weight, BMI and waist circumference. Studies were conducted between 1995 and 2016 and were conducted primarily in the United States, Canada, Iran and Brazil. The mean age of participants ranged from 26 to 67 years; nine trials included only women; nine included only men. Treatment arms used either whole, ground or deffated flaxseed (n = 22); flaxseed oil (n = 18); whole flaxseed and flaxseed oil (n = 1) flaxseed lignin (n = 5) or lifestyle advice with 30 g per day of flaxseed (n = 3). Placebo arms used interventions ranging from sunflower seed, raw rice and wheat germ to corn oil, safflower oil or lifestyle advice only. Supplementation varied from 3 to 48 weeks; many studies focused on specific disease populations, including type 2 diabetes, cardiovascular disease, obesity and hyperlipidemia.
In the 28 studies reporting body weight as an outcome measure, pooled results showed flaxseed consumption resulted in a reduction in body weight vs. placebo (weighted mean difference [WMD], –0.99 kg; 95% CI, –1.67 to –0.31) with heterogeneity (I2 = 50%; P = .001). In the 35 trials reporting BMI as an outcome measure, participants who consumed flaxseed saw a reduction in BMI vs. placebo (WMD, –0.3 kg/m²; 95% CI, –0.53 to –0.08), also with heterogeneity among studies (I2 = 54.93%; P < .001). Thirteen studies assessing waist circumference also showed a reduction after flaxseed consumption vs. placebo (WMD, –0.8 cm; 95% CI, –1.4 to –0.2) with no significant heterogeneity among studies (I2 = 46.94%; P = .027).
In subgroup analyses stratifying results by type of flaxseed intervention, researchers observed a reduction in body weight with whole flaxseed only (WMD, –1.75 kg; 95% CI, –2.87 to –0.63). Results were similar for reductions in BMI (WMD, –0.63 kg/m²; 95% CI, –1.17 to –0.09) and waist circumference (WMD, –1.21 cm; 95% CI, –1.96 to –0.46), according to researchers.
Additional subgroup analyses performed to identify the effective dose and duration of a whole flaxseed intervention on body composition showed that both body weight and BMI were reduced only with whole flaxseed doses of at least 30 g per day and only in trials lasting at least 12 weeks.
The researchers noted that the observed reduction in body composition indices with whole flaxseed may be due to the high fiber content.
“Dietary fiber, particularly soluble fiber, has anti-obesity effects that have been shown to decrease body weight,” the researchers wrote. “Dietary fiber may help prevent weight gain or promote weight loss via delayed gastric emptying, inducing feelings of fullness by absorbing large amounts of water and/or increasing the concentration of short-chain fatty acids that act to enhance satiety by a variety of mechanisms.”
Well-designed trials lasting at least 12 weeks are needed to confirm any beneficial effects, the researchers wrote. – by Regina Schaffer
Disclosures: The authors report no relevant financial disclosures.