Ground flaxseed increased nitric oxide levels in adults with type 2 diabetes: A randomized comparative effectiveness study of supplemental flaxseed and psyllium fiber

•Psyllium and flaxseeds reduce waist circumference 1-3 cm in subjects with type 2 diabetes.•Ground psyllium and flaxseed reduce MDA in subjects with type 2 diabetes.•Flaxseeds increase the vasodilator and antioxidant nitric oxide in subjects with type 2 diabetes.

Despite reported benefits of flaxseeds and psyllium, to our knowledge no studies have compared their effectiveness in adults with type 2 diabetes (T2D). While both psyllium and flaxseeds are plant-derived fibers, flaxseeds contain additional compounds associated with cardiovascular health including alpha linolenic acid, phytoestrogen lignans, vitamin E and carotenoids. The objectives were to determine primarily whether flaxseeds were more effective than psyllium at improving weight and cardiovascular health (glucose, lipids and blood pressure) and secondarily inflammation and oxidative stress in subjects with T2D. We hypothesized, when matched for fiber mass content, daily supplementation with ground flaxseeds (28 g/d) would be more effective than ground psyllium fiber (9 g/d) for improving adiposity and glycemic regulation, serum lipids, blood pressure and markers of inflammation and oxidative stress in participants with T2D. In this comparative effectiveness parallel-design study, adults (18-75y) with T2D were randomized to consume either supplement for 8 weeks with anthropometrics and blood samples collected at baseline and week 8. Flaxseed and psyllium reduced waist circumference (−2.8 ± 2.0 and −1.2 ± 2.4 cm, respectively; p = 0.002 within groups) and oxidized lipoproteins (−2.8 ± 4.2 and −0.1 ± 1.5 nM/L, respectively; p = 0.037 within groups) without affecting body mass, lipids, or blood pressure. Flaxseeds alone increased nitric oxide (+2.4 ± 3.3 vs −0.9 ± 2.7 nM/L; p = 0.044 between groups) suggesting flaxseeds may offer additional vasoprotection. Thus, fiber supplementation is an effective means to reduce waist circumference and oxidative stress in individuals with T2D. In addition, this study was the first to show that flaxseeds increase nitric oxide bioavailability in the vasculature of subjects with T2D.