Effects of a Flaxseed-Derived Lignan Supplement in Type 2 Diabetic Patients: A Randomized, Double-Blind, Cross-Over Trial

Randomized, double-blind, placebo-controlled cross-over trial in adults with type 2 diabetes and mild hypercholesterolemia in Shanghai, China. Participants were not using exogenous insulin and were asked to maintain their habitual diet during the study; 34 participants completed/analyzed the lignan phase and 34 completed/analyzed the placebo phase.

Adults in the active arm received 360 mg/day of flaxseed-derived lignan, specifically secoisolariciresinol diglucoside (SDG), taken orally as three capsules per day for 12 weeks. The placebo arm received three rice flour capsules per day. The lignan capsules were reported to contain 20% SDG, with the remaining composition including fat, protein, fiber, and carbohydrate.

Daily flaxseed-derived lignan supplementation modestly improved glycemic control by lowering HbA1c versus placebo, but it did not improve fasting glucose, insulin concentrations, insulin resistance, or lipid profiles. HbA1c changed by -0.1060.65% with lignan versus 0.0960.52% with placebo (P = 0.001). Fasting glucose, insulin, HOMA-IR, and blood lipid profiles showed no significant between-treatment differences, although HOMA-IR was reported to decrease by 3.3% from baseline during lignan treatment. Adherence was high (96% during lignan, 94% during placebo), and reported adverse events included diarrhea (23%), flatulence (32%), and nausea (4%), which were not attributed to the capsules.

The completed sample was small, with only 34 participants analyzed in each treatment phase, which limits power and precision. The intervention lasted only 12 weeks and was conducted in a single city, so longer-term effects and generalizability are uncertain. Outcomes were limited, and the cross-over design plus self-reported diet and activity monitoring may introduce residual variability.