Seven metabolites were isolated after anaerobic incubation of secoisolariciresinol diglucoside (1) with a human fecal suspension. They were identified as (-)-secoisolariciresinol (2), 3-demethyl-(-)-secoisolariciresinol (3), 2-(3-hydroxybenzyl)-3-(4-hydroxy-3-methoxybenzyl)butane-1, 4-diol (4), didemethylsecoisolariciresinol (5), 2-(3-hydroxybenzyl)-3-(3, 4-dihydroxybenzyl)butane-1, 4-diol (6), enterodiol (7) and enterolactone (8).Furthermore, two bacterial strains, Peptostreptococcus sp. SDG-1 and Eubacterium sp. SDG-2, responsible for the transformation of 1 to a mammalian lignan 7, where isolated from a human fecal suspension. The former transformed 2 to 3 and 5, as well as 4 to 6, and the latter transformed 5 to 6 and 7.