If you’re confused about which oils are safe and best for cooking, you’re not alone. Dietitian Paula Norris @movingdietitian helps to dispel some of myths and get you comfortable cooking with the best.
To understand why there is concern and confusion about cooking with oils we first need to understand what happens to oils when we heat them. Factors that affect the stability of an oil during cooking include; fat being broken down into free fatty acids (FFA) as well as oxidation of the fats. Oxidation creates polymers and polar compounds which are toxic and have been linked to cancer and diseases such as Alzheimer’s and Parkinson’s. The levels of polymers and polar compounds do not appear to be an issue in cooking at home but can become problematic in industrial kitchens where the same oil is used repeatedly to cook food, such as that in deep frying for example.
We hear a lot about ‘smoke point’ in relation to the stability of oils, however there are several other factors at play that we need to consider including:
- Anti-oxidant content of cooking oils.
- Degree of unsaturation of the fatty acids.
- Frying time and whether oils are being repeatedly used.
- Smoke point of oils compared to the temperature of the cooking method used.
Let’s break this down a little more:
Anti-oxidant content of cooking oils
Extra virgin olive oil (EVOO) and Avocado oils are the richest in Vitamin E and Polyphenols, also known as phenolic compounds, which have strong anti-oxidant properties. Phenolic compounds also have anti-inflammatory and anti-thrombotic activity. Highly refined oils such as vegetable oils and sunflower oil have minimal anti-oxidants unless they’re added post oil production. Seed oils such as sunflower, canola and sesame are more susceptible to oxidation due to their low levels of phenolic compounds.
Degree of unsaturation of the fatty acids
Poly-unsaturated fats are more susceptible to breaking down to free fatty acids due to their structure. Oils with the highest % of poly-unsaturated fats include soybean, grapeseed, vegetable and sunflower oil. Vitamin E is often added to these oils to prevent oxidation, but it’s anti-oxidant properties are not as strong as that of phenolic compounds. EVOO and Avocado oil are mono-unsaturated dominant they are less likely to be oxidised compared to poly-unsaturated fats. While avocado oil is less studied, it does have a similar nutritional profile to EVOO.
Oils highest in poly-unsaturated fats perform the worst in relation to production of toxic polar (toxic) compounds when heated, but this is usually problematic in industrial settings compared to household cooking.
Frying time and whether or not oils being repeatedly used.
Using oils over and over as in done in a commercial setting will increase the levels of free fatty acids, polymers and polar compounds which as detrimental to health. This is most common in industrial fast food style cooking. Another reason to minimise those deep-fried chips!
Smoke point of oils compared to the temperature of the cooking method used
Smoking point is literally the temperature at which any given oil starts to ‘smoke’ during cooking. We should aim for an oil with a smoke point that is higher than the approximate heat of the cooking method used. When we look at smoke point in isolation, most oils used in a single cooking session for household cooking have a smoking point higher than the cooking method used.
Most oils have a smoke point of over 180°C (350°F) – including extra Virgin olive oil. EVOO with a smoke point of 206°C. Avocado oil has a slightly lower smoke point than EVOO but is still above 180°C (350°F), this should be considered in high temperature oven baking where temps may get to 200°C (390°F) or higher. A few oils fall below 180°C including virgin olive oil at 175°C and macadamia oil at 154°C.
The approximate smoking point of cooking methods are as follows:
- Deep frying – 180° (350°F).
- Oven baking – usually 180-200°C (350-390°F).
- Pan frying (sauteing) – 120°C (250°F).
What about Coconut oil?
A few reasons why Coconut oil is not the best choice for regular use or in cooking include:
- Coconut oil is highly saturated at about 80%. While the saturated fat from coconut oil has been found to not be as bad as other saturated fats on our blood fat profile, it has still been shown to increase both overall total cholesterol and LDL (bad cholesterol).
- Most studies promoting benefits tend to be using coconut products – not extracted coconut oil. Whole coconut products have a better nutritional profile compared to coconut oil.
- Keep cooking temperatures moderate at 180°C (350°F) where possible.
- Avoid repeatedly using the same oil at home, for example if you have a home deep fryer.
- There is no benefit in choosing a higher smoke point oil when the smoke point is already above the cooking temperature.
- Consider more than just smoke point when choosing oils for cooking. In isolation smoke point is a poor predictor of the overall stability of an oil.
- The high production of ‘toxic’ polar compounds is likely to be more of an issue in the commercial setting where higher temperatures, longer cooking times and repeated use of same oil is far more likely. Another reason to limit your consumption of oily take away foods!
- Extra virgin olive oil and avocado oils produce the least polar compounds. Grapeseed oil, canola oil and rice bran oil produced the highest levels.
- Coconut oil exhibits similar effects to those of other saturated fats. Small amounts only of coconut oil or moderate amounts of whole coconut products are preferred to add flavour only.