What Is Polyunsaturated Fat?

Polyunsaturated fats are dietary fats found in certain fish, nuts, seeds, and vegetable oils. A healthy fat, polyunsaturated fats can help reduce LDL cholesterol levels and lower your risk of heart disease and stroke. 

In addition to heart health, some polyunsaturated fats have been shown to promote brain health, improve mental-health conditions such as depression, prevent Alzheimer's disease, and even aid in weight loss.

Like all fat, polyunsaturated fat is calorie dense, with nine calories per gram, compared with four calories per gram of carbohydrate or protein. If you are counting calories or watching your weight, be mindful to not overindulge.

Saturated Versus Unsaturated Fats

There are two main types of dietary fat: saturated fat and unsaturated fat. Unsaturated fats include monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs). What distinguishes these fats from one another is their chemical structure.

Saturated fats have no double carbon bonds in their molecular structure and are "saturated" with hydrogen atoms. These are fats that are solid at room temperature, such as butter and lard. High intake of saturated fat has been linked to high levels of LDL cholesterol and heart disease.

Unsaturated fats, on the other hand, have double carbon bonds. Those double bonds make unsaturated fat bendable, which is why they remain liquid, even in the refrigerator.

Monounsaturated fats have one double carbon bond while polyunsaturated fats have multiple double bonds. According the American Heart Association, swapping out saturated fat for monounsaturated or polyunsaturated fat can reduce LDL cholesterol levels and improve heart health.

PUFAs: Omega-3 and Omega-6

Polyunsaturated fats take on different forms, but the two most notable are the essential fatty acids omega-3 and omega-6. They are essential because the body cannot manufacture them, so they must be taken in through diet.

Omega-3 fatty acids are found in oily fish (such as salmon and trout), nuts, and seeds. Omega-3 fatty acids may protect against heart disease, inflammation, certain types of cancer, diabetes, Alzheimer’s disease, and macular degeneration (a leading cause of vision loss). Many people take omega-3 fish oil supplements to ensure they get enough of these beneficial essential fats in their diet.

Omega-6 fatty acids are found in nuts, seeds, and vegetable oils, such as soybean, cottonseed, corn, sunflower, and safflower oil. While still considered healthier than saturated fat, research suggests that too much omega-6 in relation to omega-3 may lead to inflammatory diseases, including cardiovascular disease, diabetes, obesity and rheumatoid arthritis.

What's more, the amount of omega-6 fat that we tend to consume has increased dramatically in recent decades, while in general the amount of omega-3 fat we consume is lower.

Health Benefits of Polyunsaturated Fats

In addition to essential fatty acids, polyunsaturated fats are rich in vitamin E, an important antioxidant with many health benefits. Replacing saturated dietary fats with polyunsaturated fats can help reduce LDL-cholesterol levels, which in turn can lower your risk for heart disease.

Ways you can swap saturated fat for healthier polyunsaturated fats include sautéing vegetables in vegetable oil instead of butter, replacing one-third to one-half of the butter in baked goods with a vegetable oil such as canola oil, and adding nuts to salad instead of cheese.

Problems with Polyunsaturated Oils

While most vegetable oils are healthy, they can sometimes go bad. Polyunsaturated cooking oils turn rancid more quickly than other fats and some evidence suggests that, in excess, polyunsaturated fat may increase your cancer risk.

Rancid Oils

To prevent cooking oils from going rancid, store in a cool, dark place before opening, and refrigerate after opening. Before using an open bottle, check for rancidity by smelling and touching the oil. If it smells metallic, bitter, or soapy, or is sticky to the touch, don't use it.

Hydrogenated Oils

Another issue with polyunsaturated oils is they are used to create trans fats, which raise LDL cholesterol levels and lead to heart disease and diabetes. Trans fats are made in an industrial process that adds hydrogen to vegetable oil creating a more shelf-stable product.

Prior to the 1990s, trans fats were considered a healthier alternative to saturated fats. Margarine, for example, is often made of trans fats and was promoted as a heart-healthy option to butter. Since the discovery that trans fats are bad, many margarine companies have reformulated their product to eliminate trans fats.

You can know if a food contains trans fats by reading the nutrition labels. Trans fats are separated under the total fat heading. In ingredient lists, the term "partially hydrogenated" before an oil indicates it is a trans fat.

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