Food
Cooking oils
Introduction
When you’re buying oil you need to consider what you’ll use it for, how healthy it is and what it tastes like.
No single oil will meet most people’s needs – you need to find a range of oils that suit your culinary needs and lifestyle. So how do you choose the right oil?
We explain which oils are best for cooking tasks, compare the fat content of common cooking oils, and explain the facts about fats and cholesterol.
Choosing the right oil
Should you use olive or canola oil, or just plain vegetable oil to stir-fry your veges? What about for drizzling on your salad?
- For everyday cooking you’ll usually want a neutral-tasting oil which doesn’t mask the flavour of your food. Regular olive oil and canola oil are good choices. Cold-pressed oils may be too strong in flavour, and are usually more expensive.
- For frying, you’ll need oil with a high smoke point. The smoke point is the temperature to which oil can be heated before it smokes and discolours. Blended vegetable oils and canola, grapeseed and peanut oil have high smoke points. Butter and table spreads have low smoke points, so they suit light sautéing rather than frying.
- For salads and stir-fries you may want an oil with a distinctive flavour – extra-virgin olive oil and avocado oil are good choices.
As a general rule nut oils are best used in cold dishes because cooking heat can destroy their delicate flavours.
Flaxseed oil (sometimes called linseed oil) shouldn’t be heated either … but it’s delicious added to smoothies or salad dressings.
Fat facts
We all love the flavour that oil brings to food. Gram for gram, however, fat contributes more kilojoules than carbohydrates or protein. All oil is 100 percent fat; cutting back can help you stay in shape.
But for the health of your heart and arteries, it’s the type of fat that matters (see “What is cholesterol?”, below).
Fats and oils are made up of fatty acids – saturated, trans, monounsaturated and polyunsaturated. All fats are made up of a mixture of these fatty acids, with one type usually predominating in each oil or fat.
Types of fat
Saturated fat
Saturated fat raises the total amount of cholesterol – and the amount of “bad” low-density lipid (LDL) cholesterol – in your blood. Saturated fats can also promote blood clotting, which can lead to a heart attack or stroke. Certain cancers (breast and bowel cancer) have been linked with high intakes of saturated fat.
Tip: Fats high in saturates are usually solid at room temperature. You’ll find saturated fat in meat, full-fat dairy products, butter, spreads, cakes and biscuits. Palm and coconut oil are high in saturated fat too.
Trans fat
This has the same effect as saturated fat because it raises both total and LDL cholesterol. Trans fat also decreases “good” high-density lipid (HDL) cholesterol levels.
Small amounts of certain trans fats occur naturally in butter, milk, cheese and meat. But the problematic trans fats are mostly formed when liquid oils are hydrogenated. This is the process of adding hydrogen, which hardens fats and makes them more stable and convenient to use.
Tip: You’ll find trans fats in some table spreads, cakes, biscuits and other processed foods. Liquid vegetable oils have negligible amounts of trans fats.
Monounsaturated fats
These are “good” fats. They lower total and LDL cholesterol and appear to have little adverse effect on HDL cholesterol. Avocado, canola, macadamia nut and olive oil are good sources of monounsaturates.
Polyunsaturated fats
These are also “good” fats that have been found to lower total and LDL cholesterol. High intakes may lower HDL cholesterol. Sunflower, safflower, soya bean and grapeseed oils are good sources of polyunsaturates.
Omega fatty acids
Omega fatty acids are polyunsaturates that are essential for health – our body can’t make them so we need them in our diet. Omega-6 fatty acids are more prevalent in the oils of seeds and grains, like sunflower and corn oil. Flaxseed and fish oils are good sources of omega-3 fatty acids. The omega-3s found in fish oils are beneficial for many conditions including heart disease, joint mobility, and brain and eye development.
What is cholesterol?
Cholesterol is a fatty substance that is essential to help build the hormones and nerve cells your body needs. But too much cholesterol may thicken the walls of your blood vessels, increasing your risk of heart disease and stroke.
Cholesterol mainly gets around in the blood attached to LDLs and HDLs as carriers.
LDLs are the “bad” form. If you have high levels of them in your blood, it’s likely some will be deposited as fatty streaks on your artery walls – which increases your risk of heart disease. In contrast, HDLs help slow this process by carrying cholesterol out of the tissues and back to the liver for processing.
The liver makes most of the cholesterol your body needs. We also get cholesterol from eating animal products such as meat, eggs and dairy products.
However, LDL-cholesterol levels are linked more strongly to your intake of saturated and trans fats than to your intake of cholesterol-containing foods. So watch out for “low” or “no” cholesterol foods that are high in saturated or trans fats.
Monos or polys?
Health experts advise replacing saturated and trans fats with monounsaturated and polyunsaturated fats. But which is better: mono or poly?
There’s no definitive answer. They both lower total and LDL cholesterol. But some studies suggest that very high levels of polyunsaturated fats can, in addition to lowering the LDL cholesterol, also lower the “good” HDL cholesterol. It’s unlikely you’d eat such high levels in a normal diet.
Polyunsaturated fats appear to be more susceptible to oxidation than monounsaturates. There’s concern that oxidised oils may have bad health effects.
On the other hand … the omega-3 polyunsaturates found in fish oils appear to decrease blood clotting, which can reduce your risk of heart disease. Monounsaturates don’t have this effect.
Tip: The best advice is to replace some of the saturated fat with a mix of monounsaturated and polyunsaturated fats, and to focus on monounsaturates and omega-3s. Many vegetable oils are low in saturated fats and either high in monounsaturated or polyunsaturated fat.
Oils compared
Guide to the table
- Oils within each category are ranked according to monounsaturated-fat content (from highest to lowest).
- A = avocado, olive and flaxseed.
- B = linseed, sunflower and almond.
Oil lingo
- Cold-pressed: The oil is extracted from the seed, fruit or nut by mechanical pressing only. There’s little or no heat to extract more oil. After it’s pressed the oil just needs to be filtered and so it tends to keep its natural flavour. You can usually tell a cold-pressed oil by its deep colour, stronger flavour and higher price.
- Expeller-expressed: These oils are obtained by squeezing the seed, fruit or nut at high pressure. Most oils are extracted by this method but don’t qualify as cold-pressed because the high-pressure squeezing generates heat. Expeller-pressed oils still retain most of their flavour, aroma, and colour.
- Refined: Most oils produced on a large scale, such as canola and sunflower, are refined. Refining involves a number of processes that include using heat and chemicals. Bleaching gives the oils a light colour, deodorising removes any aromatic oils or free fatty acids that might be left in the oil to affect flavour, and distilling removes any final material that could cause unwanted aromas. As a general rule, more refining means less flavour and colour.
- Light: It’s light – but in colour and taste only. Like every other oil, light oil is 100 percent fat. (If you want to cut kilojoules, use less.)
- “No cholesterol”: Don’t be impressed by no-cholesterol claims on oils. Cholesterol comes from animal products, so vegetable oils will contain virtually none anyway.
Olive oil
Olive oil has a reputation for being a healthy oil. The health benefits are related primarily to the oil's high levels of monounsaturated fatty acids, and to the presence of natural antioxidants. Antioxidants have been shown to protect against heart disease and cancer.
The higher cost of extra-virgin may mean you keep it for dressings or special dishes where flavour is important. In baking and stir-frying, you may prefer to use milder tasting pure or "light" oil.
- Extra-virgin: The highest grade of olive oil: it's usual to pay a premium for it. Extra-virgin's made from the first pressing of olives, and has minimal processing to maintain the flavour and aroma. As a result, it's the olive oil with the highest levels of antioxidants. Extra-virgin can't have more than 0.8% acidity and must be assessed as fault-free by an expert panel.
- Virgin: Olive oil with minor imperfections and a higher acidity level.
- Pure: A mix of refined and virgin oil, resulting in a milder olive taste.
- Light or extra-light: Refined oil with small amounts of virgin oil added. These oils are "light" in colour and taste, but they're not "light" in fat or kilojoules.
Our advice
- Choose an oil that’s low in saturated and trans fat. But remember that all oil is 100 percent fat, so use as little as possible.
- If you’re heavy-handed with your oil, measure it with a spoon. Or try a non-stick oil spray – the amount that comes out in a spray is small, and so it’s easier to use less.
- Heat and light can affect oil quality. Try to avoid oils that have been displayed in a shop window or under fluorescent lights. Green or dark bottles – or tins – provide better protection from the light. Store your oil in a cool dark place.
- Oils don’t improve with age. So buy the freshest oil possible. Look for a pressed-on date if there is one: best-before dates aren’t always a good indicator of quality because you don’t know how old the oil is.
What about takeaways?
You can choose your oil at home but not when you eat out.
Some fast-food companies are using healthier cooking oil. When we tested hot chips in 2008 we found Domino’s Pizza, Burger Wisconsin and Nando’s used canola oil. McDonald’s used high-oleic vegetable oil and Burger Fuel used a vegetable blend.
But fast-food giants KFC, Pizza Hut and Burger King were still using “unhealthy” palm oil or beef tallow – both of these are high in saturated fat. We’d like all takeaway outlets to use healthier oils.
Tip: Check that your takeaway outlet uses one of the healthier oils for frying. If it doesn’t, get your takeaways from somewhere that does.
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Report by Belinda Allan.