Flaxseeds are known already for a long time for their positive health effects. The high content of dietary fiber, the advantageous fatty acid composition and the lignans are held responsible for this. Lignans are compounds, which have a similar structure as human estradiol. As a result of that, they are expected to influence hormone metabolism, and (beneficially) influence human health. However, the lignans from flaxseed are not bioactive themselves. They need to be bioactivated by the bacteria in the human intestinal tract. Firstly, it was investigated how lignans are present in flaxseed. Lignans were found to form oligomeric molecules together with other components. These oligomeric molecules are called the lignan macromolecule. Secondly, it was investigated, which microorganisms are involved in the bioconversion reaction and we isolated the formed bioactive lignans. Via this procedure bioactive lignans has been obtained, which can be used as a functional food ingredient.