Flaxseed and flaxseed oil (or linseed oil) are rich sources of the essential fatty acid alpha-linolenic acid (ALA). In the body, some ALA is converted to omega-3 fatty acids.
Lignans are a type of plant hormone similar to estrogen. The lignan components of flaxseed (not flaxseed oil) may possess antioxidant properties and alter estrogen activity.
As a source of fiber, flaxseed (not flaxseed oil) has laxative properties. In large doses, or when taken without enough water, flaxseed may cause bowel obstruction. The effects of flaxseed on blood sugar levels are unclear.
Flaxseed oil contains only the ALA component of flaxseed and not the fiber or lignan components. Therefore, flaxseed oil may share the potential cholesterol-lowering properties of flaxseed, but not the proposed laxative or anticancer abilities.