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The Ultimate Guide to Cooking Oils

Oils prevent food from sticking to pans, allow roasted vegetables to become crispy, add moisture to baked goods, and provide salad dressings with their creamy mouthfeel. But not all oils are created equally. With so many options to choose from, how can you be sure you’re selecting the best one? Which oil should you use for high cooking temperatures? Is canola oil really inflammatory? And what exactly does “extra virgin” mean? Keep reading to learn everything you need to know about oils, from a dietitian’s perspective.

 

First, let’s go over some oil basics.

Characteristics of oils

Smoke point

Smoke point is the temperature at which an oil begins to produce smoke and oxidize, or react with oxygen and deteriorate. We want to avoid reaching the smoke point, because burnt oils produce inflammatory free radicals and create unpleasant, toxic fumes which may set off your smoke alarm. Since each oil has a different smoke point, certain varieties are better for high cooking temperatures, and others best to reserve for low heat cooking or dressing.

Degree of saturation

The degree of saturation refers an oil’s chemical structure. It influences both its health effects and tendency to oxidize. Oils are comprised of monounsaturated fats, polyunsaturated fats, and saturated fats. Each oil contains a different mixture of the three, but one type of fat will usually predominate.

Saturated fats are solid at room temperature and most stable due to their chemical structure. Unfortunately, they tend to raise LDL cholesterol (also referred to as “bad cholesterol”). Monounsaturated fats are thought to lower LDL when they replace saturated fats in our diet, but are slightly less stable. Polyunsaturated fats are most prone to oxidation, but may also lower LDL and increase HDL cholesterol (the “good cholesterol”) when they replace saturated fats in our diet, thereby lowering our risk for developing heart disease.  

Refined vs unrefined

If an oil is refined, it has been treated with chemical solvents and heated as part of the extraction process. While this method is economical, it also results in a highly processed product with fewer beneficial polyphenols and antioxidants. Oils like canola, soy, corn, vegetable, and sunflower are commonly refined. Unrefined oils, on the other hand, are extracted via a mechanical process such as pressing.

Partially hydrogenated oils

Trans fats have clearly been demonstrated to increase heart disease risk. They have largely been removed from our food supply, but still exist in some foods, and food companies aren’t always upfront about it. While small quantities of trans fats exist naturally in certain foods like dairy products, most of the trans fats we consume come from partially hydrogenated oils.

Partially hydrogenated oils are produced when oil is chemically engineered to be solid at room temperature, by adding extra hydrogen. Even if a food is labeled as “free from trans fats,” it may contain up to 0.5 grams of trans fats per serving. This is because the Food and Drug Administration (FDA) allows companies to round down to 0 grams if their product contains 0.5 grams or less of trans fat per serving. If you’re like most people and consume more than the recommended serving size, or more than one serving of that food each day, before you know it, you will have eaten a few grams of harmful trans fat without realizing it. This may not sound like much, but trans fats can increase atherogenic LDL cholesterol and lower cardio-protective HDL cholesterol even when small quantities are consumed. Fortunately, you can still determine whether or not a food contains trans fat by scanning the ingredient list for “partially hydrogenated oils.” Fig’s browser extension and mobile app (still in beta) can help you do this easily!

A Breakdown of Common Cooking Oils

Avocado oil

Just as avocados are filled with heart-healthy monounsaturated fats, their oil is, too. Avocado oil is often produced in a similar manner to olive oil, through mechanical extraction, although refined versions exist as well. It is an excellent choice for cooking under moderate to high temperatures, since it has a relatively high smoke point compared to other plant oils. For unrefined versions, you can roast, grill, and pan fry at temperatures up to 375° F without worry. If you use refined avocado oil, this increases to an impressive 480° F. Avocado oil has a neutral flavor, so you can add it to anything from baked goods to salad dressing without altering taste.

Canola oil

Canola oil is derived from the rapeseed plant and contains predominantly monounsaturated and polyunsaturated fats. It is inexpensive due to governmental subsidies of the canola industry, and is useful for cooking and baking at temperatures up to 400° F. Historically, canola oil was considered a healthy oil because it is very low in saturated fat. More recently, however, it’s been labeled by mainstream media as inflammatory.

The truth is that while canola oil is low in saturated fat, it’s also heavily processed. Most canola oil is extracted using hexane, a chemical solvent, in addition to high heat. Exposing oils to high temperatures “deodorizes” them, to create a neutral-tasting end product. The high temperatures used for deodorization impact the stability of the oil, causing it to go rancid. Studies suggest that such high temperatures may also create small amounts of trans fats within the oil. Additionally, concerns have been raised about hexane residues lingering in canola oil and their potential impact on human health. Canola is also one of the most common genetically modified (GMO) crops in the U.S., so most canola oil is made from GMO rapeseed. GMO crops are often bred to withstand pesticides like glyphosate, raising concern that canola oil may contain glyphosate residues.

Coconut oil

Coconut oil has been subject to great controversy over the years. It was once demonized as an artery-clogging oil due to its high saturated fat content, but in more recent years, has been touted as a cure-all for a variety of ailments. Coconut oil is unique because it’s one of the few plant oils comprised of over 90% saturated fat. While this is generally not ideal from a cardiovascular health standpoint, its high level of saturation makes coconut oil more heat stable and less likely to oxidize. It’s solid at room temperature, making it useful for baking as a plant-based butter replacement. It also lends a subtle coconut flavor to foods.

Coconut oil is available in refined and unrefined, “virgin” varieties. Virgin coconut oil has a stronger flavor but a lower smoke point of 350° F, whereas refined coconut oil has a milder flavor and higher smoke point of 400° F. Research on coconut oil’s cardiovascular effects yield mixed results. Some studies demonstrate coconut oil raises HDL but does not raise LDL as significantly as other saturated fats like butter. Other studies demonstrate that coconut oil significantly raises LDL when it replaces unsaturated plant oils in the diet. It is likely that different individuals may have varying responses to coconut oil based on genetics and other factors. Generally speaking, it’s probably best to consume coconut oil in moderation.

Corn oil

Corn oil consists of mostly polyunsaturated fat and is commonly used for its low cost, neutral flavor, and high smoke point of 450° F. It is often used for frying and other high-heat cooking methods. Corn oil is always refined, as it’s not possible to extract much oil from corn without heavy processing. Corn oil does contain some vitamin E, a fat-soluble vitamin with antioxidant properties. Nevertheless, it has a high omega-6 to omega-3 ratio, which is not ideal. Most of us don’t consume nearly enough omega-3 fatty acids, but far too many omega-6 fatty acids. This can promote inflammation in the body, since omega-3 fatty acids oppose inflammatory processes.

Similar to canola oil, corn oil is commonly treated with hexane solvents and nearly 90% of U.S. corn is genetically modified, raising concerns for potential glyphosate contamination.

Grapeseed oil

While grapeseed oil has a moderately high smoke point of 420° F, it consists of mostly polyunsaturated fats, making it more prone to oxidation. It is most commonly produced through chemical extraction unless otherwise specified, and like corn oil, contains vitamin E. Similar to other vegetable oils like canola and sunflower, it has a high in omega-6 to omega-3 fatty acid ratio, so it’s best to consume in moderation.  

 

Olive oil

Olive oil is one of the healthiest oils out there. It’s high in antioxidants and has been linked to heart disease prevention and longevity. Olive oil contains a high percentage of monounsaturated fat and is produced by grinding olives into a paste, then pressing them to extract their oil. While many types of olive oil exist, extra virgin is the cream of the crop. “Extra virgin” means the oil hasn’t been treated with chemical solvents or high temperatures, and it must meet certain specifications like having a particular acidity. Extra virgin olive oil also retains much of its olive flavor and aroma since it’s unrefined.

One downside of extra virgin olive oil is that compared to other oils, it has a slightly lower smoke point, between 350° F and 375° F, so if you use it for cooking under very high temperatures, it’ll oxidize and burn. Interestingly, despite its lower smoke point, studies suggest olive oil produces fewer toxic compounds when heated to frying temperatures compared to other vegetable oils like canola and sunflower.

Palm oil

Similar to coconut oil, palm oil is predominantly saturated fat. It has a high smoke point of 450° F and is semi-solid at room temperature. It comes from the fruit of oil palm trees, found in parts of Asia and Africa. While unrefined versions are available, pam oil is often refined. Due to its high saturated fat content, it raises cardiovascular health concerns, but the sustainability concerns associated with palm oil production are even more worrisome. Palm oil production is linked to rainforest destruction, habitat degradation, and loss of rainforest biodiversity. In the U.S., it isn’t as commonly used for cooking, but is often found in packaged foods, like peanut butter, chocolate, and baked goods.

Vegetable oil

When you hear the word “vegetable,” you may automatically think healthy, but when it comes to oil, this is not always the case. Vegetable oil can technically come from any plant, but most commonly is a blend of one or more of the following oils: soybean, corn, canola, sunflower, safflower, and cottonseed.

Vegetable oil is highly refined through high heat and chemical solvent extraction methods to produce a large volume of odorless, flavorless, multipurpose oil with a high smoke point. Studies demonstrate that when vegetable oils are heated, toxic compounds called aldehydes are produced, which increase chronic disease risk. According to recent research, this phenomenon is most pronounced in sunflower oil, a common constituent of vegetable oil. This doesn’t bode well for fried foods, which are commonly cooked in vegetable oil at high temperatures.

The bottom line

When selecting a cooking oil, there are many factors to take into consideration. Based on the  available scientific evidence, I generally recommend olive oil for cooking at low to moderate temperatures and dressing, and avocado oil for cooking at higher temperatures. These two oils tend to be the least refined and have more favorable omega-6 to omega-3 fatty acid ratios.

That being said, based on your specific dietary needs, financial constraints, access, and intended use, other oils may be preferred and there is no right or wrong. While some oils are healthier than others, at the end of the day, it’s important to remember that ingesting small quantities of less healthful oils from time to time will not make or break your health. That said, being selective with which oils you purchase and paying attention to oils listed on ingredient labels of foods you consume, is a beneficial health practice to adopt.

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Rachel Dyckman, MS, RDN, CDN

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