Food-grade flaxseed oil is cold-pressed, obtained without solvent extraction, and marketed as edible flaxseed oil. Fresh, refrigerated and unprocessed, linseed oil is used as a nutritional supplement. It contains high levels of omega-3 fatty acids, especially alpha-linolenic acid, which has been suggested to be beneficial for reducing inflammation leading to atherosclerosis, preventing heart disease and arrhythmia, and is required for normal infant development. However recent well-controlled placebo studies suggest that regular consumption of flax seed oil may not reduce the risk of stroke, heart disease, or cancer any greater than placebo. Regular flaxseed oil contains between 52 and 63 % alpha linolenic acid . Plant breeders have developed flaxseed with high alpha linoleic acid content (70 %) and very low alpha linolenic acid content (< 3%). Although flax seeds themselves contain lignans, a class of phytoestrogens considered to have antioxidant and cancer preventing properties, the extracted linseed oil does not contain the lignans found in flax seed, and therefore does not have the same antioxidant properties. In fact, flax seed oil is easily oxidized, and rapidly becomes rancid with an unpleasant odor unless refrigerated. Even when kept under cool conditions it has a shelf life of only a few weeks. Oil with an unpleasant or rancid odour should be discarded. Rancid oils contribute to the formation of free radicals and may be carcinogenic. Oxidation of flax seed oil is major commercial concern, and antioxidants may be added to prevent rancidification.