Cooking oil is a basic and essential ingredient in every kitchen, and whether you’re baking, sautéing, frying, or drizzling, choosing the right one can be confusing. Then of course there are health concerns, particularly around the type of fats they contain. This article takes a close look at the common culinary oils and the proper use of each one.
Cooking Oils 101
Cooking oils are fats derived from plants, nuts or seeds. All oils have a similar energy content (roughly 650–700kJ per tablespoon), however they differ in both the types and ratio of fats they contain; how they are made; and how they react to heat. Not only do these differences make some oils healthier than others, but more suitable for certain cooking methods.
Smoke point controversy
The smoke point of an oil is the temperature at which an oil starts to smoke constantly. At this point, it is widely believed that the oil’s physical and chemical makeup can start to change, producing toxic by-products which may be harmful to our health, despite limited evidence to support this. So, when information about the smoke point of various cooking oils began to surface, Extra Virgin Olive Oil (EVOO) got a bad rap – deemed unfit for cooking due to a relatively lower smoke point. This meant people thought that EVOO was best suited for drizzling and bread dipping.
However, recent research debunks this myth. In the study, EVOO and other common cooking oils were heated up to 240°C (464°F) over 20 minutes and exposed to 180°C (356°F) for 6 hours, with samples assessed at various times. Various parameters including smoke point and oxidative stability were measured along the way, and how well they correlated with the oil breaking down and forming harmful by-products called ‘polar’ compounds. Of all the oils tested, EVOO was the most stable when heated, producing the lowest level of polar compounds. Results also showed that oxidative stability – not smoke point – is a major factor when assessing how stable an oil is when exposed to high temperatures.
In fact, smoke point correlated quite poorly with how likely an oil was to breakdown and form harmful polar compounds.
Contrary to popular belief, Canola Oil and other seed (vegetable) oils were least stable when heated and more readily broke down and formed polar compounds, despite a higher smoke point. This is because they are refined oils, higher in polyunsaturated fats which more readily break down, and are low in natural antioxidants.
Key message: When it comes to health, the priority is to choose a cooking oil that produces the lowest amount of harmful polar compounds after heating. Despite the widespread belief of being healthy, oils with a high smoke point, such as Canola Oil, Sunflower Oil and Grapeseed Oil produced the highest levels of harmful compounds.
The more an oil can resist reacting with oxygen and breaking down, the safer and more stable the oil is to cook with. EVOO is both safe and stable for cooking, and far healthier than the other oils tested.
How the different cooking oils stack up
Choosing the right oil for your cooking
- Extra Virgin Olive oil (EVOO) is the highest grade of olive oil, naturally extracted from the fruit of the olive tree. This process is done via mechanical pressing without heat or chemicals. As a result, it retains maximal levels of naturally occurring antioxidants from the olive fruit to fight against oxidation and improve heat stability.
EVOO contains a high proportion of monounsaturated fats (70%) in the form of oleic acid, with small amounts of polyunsaturated fats (10%), which are less stable when heated.
Common uses: EVOO is a safe, stable and desirable oil to cook with and is an excellent multi-purpose oil for high temperature cooking including baking, frying and sautéing. Rich in flavour, it’s also great for salad dressings, dipping, drizzling and marinades.
- Olive oil is a blend of refined olive oil and natural olive oils. The refining process involves high heat, chemicals and processes such as bleaching and deodorizing. Similar to EVOO, it contains high levels of monounsaturated fats, but the refining process strips the oil of most naturally-occurring antioxidants found in unrefined oils that contribute to its health benefits and taste and may produce trans (unhealthy) fats.
Common uses: Less versatile than EVOO due to breaking down more readily under heat, and not as flavorsome for drizzling due to its neutral flavour.
- Canola Oil (rapeseed) is extracted from rapeseed plants. This requires refining processes such as high heat, high pressure and/or chemicals to bleach, deodorize and neutralize the oil. Relatively high in monounsaturated fats (63%) and polyunsaturated fats (32%), it also has the lowest amount of saturated fat (8%) and the most omega-3 fats of any of the common cooking oils, although plant sources of omega 3 fatty acids are linolenic acid and are not readily converted in humans to the form of omega 3 (EPA, SHA) that provide health benefits. However, as it is a refined oil, it is low in natural antioxidants. It is also naturally higher in polyunsaturated fat, and it’s the least stable when heated, producing the most harmful polar compounds. This raises questions about the healthiness of the canola oil for cooking.
Common uses: Canola Oil is typically used for home cooking and in food service due to its low cost.
- Rice Bran Oil is extracted from the germ of rice grains using refining methods similar to what are used to make Canola Oil. An antioxidant has been identified in Rice Bran Oil called oryzanol – shown to block the absorption of cholesterol into the body. With a good balance of both mono and polyunsaturated fats, it does contain slightly higher amounts of saturated fats (20%) compared to Canola Oil. However, despite Rice Bran Oil being marketed for its high smoke point and suitability for cooking, like Canola Oil, it has been shown to be the least stable and produces high level of harmful by-products. This is due to the refining methods used to extract it/ along with the higher polyunsaturated fat content and low levels of natural antioxidants
Common uses: Rice Bran Oil is typically used in home cooking for stir-frying due to marketing of its smoke point, despite this being a poor predictor of suitability for cooking.
- Coconut Oil is extracted from the flesh of the matured coconut. Despite its very high saturated fat content (92%), the jury is still out on just how healthy it is. Unlike fats from animal sources, coconut oil is composed largely of lauric acid, a type of saturated fat, which tends to mimic healthy unsaturated fats by boosting HDL (good) cholesterol. However research shows that it also raises LDL (bad) cholesterol just like other saturated fats, such as butter.
Similar to EVOO, Coconut Oil is stable and safe for cooking, however it has only trace amounts of antioxidants that protect against heat damage and is predominantly saturated fat. Granted it may be a better choice than oils such as Canola Oil, Coconut Oil is still not recommended as a suitable alternative to unsaturated oils, such as EVOO.
Common uses: Often used in sautéing dishes that benefit from the strong coconut flavour, such as curries or stir-fries. It is also suitable for high temperature cooking due to its high oxidative stability. Often used in baking and sweet dishes that require a stabilizing element.
- Sunflower Oil is extracted from the seeds of sunflowers, again using refining methods. Sunflower oil contains only 13% saturated fat and has a high proportion of omega-6 polyunsaturated (66%), which has been shown to lower cholesterol, particularly the “bad” LDL cholesterol. However, as with most oils rich in polyunsaturated fats (e.g. Canola, Sunflower and Rice Bran), it is more prone to oxidising at high temperatures, forming harmful by products.
Common uses: Similar to Canola Oil, Sunflower Oil is typically used for stir-fries and sautéing despite being less stable to cook with and more prone to breaking down and forming harmful compounds.
- Avocado Oil is extracted from ripe avocados, after the skin and seed are removed, by pressing the pulp of the fruit and separating the natural oil in a centrifuge. With its high monounsaturated fats (68%), it has a similar fatty acid profile to Olive Oil, however its naturally lower in antioxidants making it less suitable for high temperature cooking.
Common uses: With a hint of avocado flavour, this oil works well in a salad dressing.
EVOO, followed by Coconut Oil, is the most resistant to heat and therefore the most suitable for all home cooking. However, on the health balance scales, EVOO is still the standout choice. Seed (vegetable) oils produce the most harmful compounds and are a poor choice. In addition, oils with a high smoke point, such as Canola Oil, Rice Bran Oil and Grapeseed Oil produce the most harmful compounds when heated at standard cooking temperatures (for all home cooking, including high-heat cooking e.g. oven baking, pan frying and even deep-frying). This demonstrates that smoke point is a poor indicator of oil’s cooking qualities.
Although the generation of polar compounds with temperature and time was more pronounced for refined seed (vegetable) oils, it is important to note that experiments were carried out without food being cooked. The absence of food in these experiments may have allowed for a greater impact of oil oxidation when compared with deteriorations reactions. To date, limited evidence is available and further research is required to test the generation of polar compounds with high temperatures with food being cooked.
In addition, for many cooking oils, such as Canola Oil, there is limited high-quality published research to assess the safety and suitability when cooking/heating. This is an emerging area, and presents an opportunity for future research in the field.