For heart-healthy eating, we're advised to use plant-based cooking oils. But how do you get the best out of the oils you use in the kitchen?
When it comes to healthy eating, we're told to use plant-based cooking oils rather than butter, lard and animal fats. That's because most plant-based oils are much lower in the saturated fat that's bad for our hearts and richer in the polyunsaturated and monounsaturated fats that can actually do our hearts some good.
But with so many different oils on the market, which ones should you go with? Should you only stock your pantry with extra virgin olive oil because it is a rich source of antioxidants thought to help ward off diseases like cancer? Or are the cheaper, refined olive oils good enough? And what about the myriad other oils on the supermarket shelf?
The choice depends in part on how you intend to use them in the kitchen. That's because different oils are better suited to different culinary uses, and some cooking methods can actually destroy much of the goodness in some oils. So it pays to inform yourself before you buy.
Pick of the crop
In terms of overall health benefits, extra virgin olive oil and canola oil are the best choices, says Associate Professor Catherine Itsiopoulos, head of dietetics at La Trobe University and spokesperson for the Dietitians Association of Australia.
Although extra virgin olive oil does contain saturated fat (around 12 per cent), it is one of the few unrefined oils. This means that the antioxidants present in the original fruit are retained because the oil is extracted by machine only and not "refined" with chemicals or other means that can strip the goodness from the oil.
While most canola oil products are refined and don't contain many antioxidants, they have the advantage of even less saturated fat than olive oil – around eight per cent.
"A daily amount of these oils would be about two to three tablespoons ... which would be perfectly in keeping with a healthy balanced diet, and even a weight-loss regime," says Itsiopoulos.
She adds that flavour and personal preference also need to be factored in because the right oil can improve the satiety we get from our food, preventing us from overeating or snacking after meals.
"Peanut oil, for example, is a monounsaturated fat so in terms of the type of fat content it is similar to olive oil, and because it is an important part of Asian cuisine there is no good reason to remove it from your diet," she says.
She recommends, therefore, using extra virgin olive oil for cold dishes (i.e. with salads and breads) to take advantage of the flavours and antioxidants; refined oils such as canola, sunflower and plain olive oil for cooking (i.e. casseroling, sautéing and stir-frying); and peanut oil and other flavoured oils (i.e. sesame, macadamia) in dishes that demand certain flavours.
Meanwhile, tropical oils, such as palm, cottonseed and coconut, should be limited because they are naturally more saturated.
Getting the best from your oil
Unlike fine wine, oils don't improve with age. If you like to keep your good oils for special occasions, don't.
Rod Mailer, an oils researcher and adjunct professor at Charles Sturt University, explains that light, temperature and air cause oils to oxidise – become rancid or "off" – and break down, changing the flavour and colour of the oil.
"Olive oil is usually good three to 12 months after it has been bottled. After two years you would expect the fruity flavours would be disappearing and some of the bad (i.e. bitter) flavours would be coming in," he says.
"If oil was 100 years old it probably wouldn't kill you, but it would taste pretty bad."
There are numerous factors that affect an oil's stability (i.e. how fast it oxidises), including how refined it is and its proportion of saturated and unsaturated fats.
But the best way to preserve all oils is to buy them as local and fresh as possible, to store them properly and to buy in smaller quantities so they are not sitting in your cupboard for long periods.
"If you want to keep oil in good condition, keep it cool, sealed and out of the light," says Mailer. He suggests buying oil in tins or keeping your glass oil bottles in wine cellar bags (insulated foil-lined cooler bags) as they stop heat, light and air getting in.
Because heat causes oils to oxidise faster, the best ones to cook with are those that are refined, such as plain olive oil, canola and sunflower.
"You wouldn't use an expensive, high quality [unrefined] olive oil if you are going to throw it onto the hotplate of the barbecue because a lot of those flavours go up in the air and you lose them. Also, when you heat oil too much you lose the antioxidants," explains Mailer.
Secondly, refined oils tend to have a higher smoke point, which means they can be heated to a higher temperature before starting to burn and smoke.
Heating oil too much – i.e. until it is smoking – can change its chemical composition and actually be harmful to our health when we digest it, and even inhale the fumes.
Polycyclic aromatic hydrocarbons (PAHs), chemicals believed to be carcinogenic, may be formed when you heat fats and certain foods such as fatty meats at very high temperatures (i.e. deep-frying, or barbecuing and stir-frying on very hot surfaces.)
Itsiopoulos adds that Advanced Glycation End Products (AGEs) are also produced when foods (particularly meat and potato chips) are browned. These are believed to be associated with an increased risk of age-related diseases such as Alzheimer's, heart disease, stroke and cataracts.
"The barbecuing and frying process [often using oil] will brown the food, producing these chemicals called AGEs," she says.
But with the jury still out on the safe level of exposure of these impurities and the long-term effect on health, Itsiopoulos stresses we don't have to panic about cooking with oils or eating browned or fried foods occasionally.
"The occasional or irregular fried meal will not cause any harm when the rest of your diet is fairly healthy," she says.