'Good' versus 'bad' fat: Here's the difference between 5 types of fat found in your diet

In order to understand the benefits of monounsaturated fats, you first need to understand the two types of cholesterol. High-density lipoprotein cholesterol, known as HDL or “good cholesterol,” can protect your heart. It carries low-density lipoprotein cholesterol (LDL or “bad cholesterol”) from your arteries to the liver, where the bad cholesterol can be converted to energy and waste.

Monounsaturated fats promote healthy cholesterol levels and help reduce LDL levels. This fat can be found in plant sources such as avocados; nuts such as almonds, pecans, and cashews; and various oils, including olive, peanut, canola, and sesame oil. It is also present in chicken, pork, and beef.

In addition to aiding in the reduction of LDL, monounsaturated fats are also a source of Vitamin E, which is an antioxidant that contributes to reproductive, tissue, and eye health. Using olive oil instead of butter when cooking is an example of how to reduce unhealthy fats in your diet. Another example is snacking on nuts instead of chips or cookies.

All fat is relatively high in calories at 9 calories per gram, so while making sure monounsaturated fat makes its way into your diet regularly, it is important to consume in moderation.

Polyunsaturated fats have antioxidant and anti-inflammatory properties, which reduce one’s risk for disease. Polyunsaturated fats are essential for brain function and cell growth; blood pressure and blood clotting management; and nervous system response. There are two main types of polyunsaturated fatty acids: omega-3 and omega-6. 

Omega-6 fatty acids help manage blood sugar levels and blood pressure, as well as reduce one’s risk for diabetes and heart disease. While the human body can produce nearly all the fatty acid it requires to function, it cannot naturally produce linolenic acid, which is a key omega-6 fatty acid. A balanced diet that includes whole-grain carbohydrates, seeds and nuts, and plant oils such as sunflower or corn oil is the only way for the body to get the omega-6 it requires.

Omega-3 fatty acids are another form of polyunsaturated fat. They aid overall physical function and the body’s metabolism. Omega-3 fatty acids have been shown to be good for the heart by reducing the buildup of plaque in the arteries and may help reduce the risk of stroke, cancer, the flare-up of arthritis, and inflammation.

There are two categories of omega-3 fats; the first consists of EPA and DHA (eicosapentaenoic acid and docosahexaenoic acid), which are generally found in seafood, notably salmon, tuna, shellfish, and herring.

The other type is alpha-linolenic acid, better known as ALA, which comes from flaxseeds, walnuts, and some vegetable oils. Linseed and canola oils are significant sources of ALA. The USDA’s 2020–2025 Dietary Guidelines for Americans 2015–2020 recommends adults eat at least 8 ounces of seafood per week in order to get the full spectrum of benefits it provides, including lean protein and polyunsaturated fats.

Omega-3s are also available as dietary supplements. Fish oil supplements contain omega-3 in the EPA and DHA form, whereas flaxseed oil supplements contain ALA.

Saturated fats are what’s known as solid fats because they are usually solid at room temperature. When you see a finely marbled steak at the grocery store, the white in the marbling is solid fat. Saturated fats exist naturally in animal-based foods, notably beef and pork. Saturated fat has been shown to increase the risk of heart disease due to the build-up of low-density lipoprotein (LDL) in the arteries. Alongside this risk comes a heightened risk for obesity and stroke.

Saturated fats exist in many processed foods that are widely popular in America, such as pizza, fast food, and fried foods. The USDA’s most recent iteration of its Dietary Guidelines for Americans recommends limiting saturated fat to no more than 10% of total caloric intake per day, whereas the American Heart Association recommends no more than 6%.

Trans fat is a manufactured product created by adding hydrogen molecules to vegetable oil, a process known as hydrogenation. So when you see “hydrogenated” on a food label, what that means is the product contains trans fats.

One reason trans fats became so prevalent in our food system is they are inexpensive, accessible, and have a long shelf life. Restaurants with commercial fryers found value in trans fats since it could be reused to deep-fry foods, such as fries and breaded chicken products. But that’s not all—trans fat can and does exist naturally in food products such as milk, butter, and cheese, as well as meat products sourced from ruminant animals (e.g. deer, sheep, and goats).

Trans fat is generally considered to be the unhealthiest of all dietary fats—it is a prime constituent of foods that generally lead to weight gain, diabetes, and cardiovascular issues. These include battered and fried food, and mixes used for cakes, pies, and other pastries. Trans fat raises LDL (or “bad cholesterol” levels) and lowers HDL (“good cholesterol”).

The world’s leading nutritional and research bodies have taken up the fight against trans fat. The USDA’s Dietary Guidelines for Americans recommends daily trans fat daily intake be as low as possible without compromising overall nutritional value.

As of June 2018, partially hydrogenated oils can no longer be added to foods, per the U.S. Food & Drug Administration. The World Health Organization released a strategic action package called REPLACE to eliminate industrially produced trans fats globally by 2023.