Polyunsaturated fats come mostly from plant sources like nuts, seeds, and vegetable oils and include omega-3 and omega-6 fats. These fats are liquid at room temperature and often stay liquid when refrigerated. Fish is also a good source of polyunsaturated omega-3 fats, especially cold water, oily ocean fish. So unless you're a vegan or vegetarian, you should eat at least three servings of fish each week. Most red meat is low in polyunsaturated fats, but animals raised on grass instead of corn-based feeds have meat that has more polyunsaturated fats and lower in fat in general.
Omega-3 fatty acids may help prevent and even treat heart disease and stroke. In addition to reducing blood pressure, raising HDL, and lowering triglycerides, polyunsaturated fats may help prevent lethal heart rhythms from arising. Evidence also suggests they may help reduce the need for corticosteroid medications in people with rheumatoid arthritis. Studies linking omega-3s to a wide range of other health improvements, including reducing risk of dementia, are inconclusive, and some of them have major flaws, according to a systematic review of the evidence by the Agency for Healthcare Research and Quality.
Fats — or triglycerides — are made up of glycerol (an alcohol) and fatty acids, which are long carbon-hydrogen chains that end in a carboxyl group. Triglycerides are either saturated (with hydrogen) or unsaturated. Saturated fatty acids contain carbon atoms that connect with each other in a chain of single bonds . So each carbon atom can bond with two hydrogen atoms, and is said to be "saturated" with hydrogen. Unsaturated fatty acids contain some carbon atoms that bond with each other using double bonds. So these carbon atoms can only bond with one hydrogen atom instead of two, and are said to be "unsaturated".A fatty acid with a single double bond is a monounsaturated fatty acid, while a fatty acid with two or more double bonds is known as a polyunsaturated fat.