Flaxseed contains several different biological compounds that are responsible for its effect on cholesterol, blood pressure, high blood glucose, and several other positive effects.
Flaxseed contains both soluble and insoluble fiber. Soluble fiber helps to modulate glucose levels, particularly just after eating. Insoluble fiber can increase insulin sensitivity. Fiber also increases satiety, reduces the rate of glucose absorption through the intestine, and increases the excretion of cholesterol.[1][2]
Alpha-linolenic acid (ALA) is the omega-3 fatty acid found in flaxseed. ALA is used by the body in several cellular processes, and ALA can also be converted into eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), although this process is not efficient. EPA and DHA are the omega-3 fatty acids that are found predominantly in seafood sources. Flaxseed can therefore be a useful way to supplement omega-3 fatty acids, especially in people who do not regularly eat seafood or choose to follow a vegetarian or vegan diet. ALA may have some benefits for cardiovascular disease[3] and might have anti-inflammatory properties.[4] These effects could occur through the reduction of inflammatory markers like C-reactive protein (CRP) and interleukin 6 (IL-6),[5] but the evidence for this is not consistent.[1]
Lignans are phenolic compounds that are found in flaxseed, and they are converted from plant lignans to biologically active mammalian lignans by the intestinal microbiota. They are thought to have several positive effects, including antioxidant, anti-inflammatory, and weak estrogenic effects.[1]
Flaxseed also contains several minerals, such as calcium, magnesium, and phosphorus, all of which are important in blood pressure regulation, muscle contraction and relaxation, and several cellular functions. Along with the small amount of vitamin E found in flaxseed, these may also contribute to the anti-inflammatory and antioxidant effects.[1]
Phytoestrogens (e.g., lignans) and vitamin E play an important role in cellular regulation, in particular in angiogenesis (the growth of new blood vessels) and cell apoptosis (natural cell death). This could result in flaxseed having an anticancer effect. These effects have been observed in animal models and have not yet been confirmed in human studies.[1]