Flaxseed Lignans (Secoisolariciresinol Diglucoside)

Secoisolariciresinol diglucoside (SDG) is the main lignan of flaxseed; gut bacteria convert it to the enterolignans enterodiol and enterolactone, which have weak oestrogenic/anti-oestrogenic and antioxidant activity. Human evidence is small-trial and mixed: an 8-week RCT (Zhang 2008, n=55) found 300–600 mg/day lowered total/LDL cholesterol and glucose in hypercholesterolaemic adults; a 2024 Japanese RCT found 60 mg/day lowered LDL in men with borderline LDL only; a 4-month RCT (Zhang 2008, n=87) reported improved IPSS symptom scores in benign prostatic hyperplasia at 300–600 mg/day; a 12-week trial in type 2 diabetes found mainly increased bleeding time and a smaller waist gain after correction for multiple comparisons; a rye+SDG crossover (Eriksen 2020) found no glucose effect. There are NO clinical trials supporting flax lignans for hair growth or hair loss, despite their inclusion in hair-supplement formulas on a 5-alpha-reductase rationale. Generally well tolerated; mild GI effects; because of oestrogenic activity, caution in hormone-sensitive conditions and pregnancy is customary. Do not confuse with sesame lignans (sesamin) or HMR lignan (7-hydroxymatairesinol from spruce), which have separate entries.

Limited clinical evidence. Handful of small RCTs (n=55–87) at 60–600 mg/day with modest, inconsistent lipid/BPH effects; no hair-loss trials exist