Choosing cooking oils

Published: 11 April 2024

How do you choose the right oil for your cooking and which oils are best for our hearts? Here you’ll find everything you need to know about vegetable oils to help you make the best choice from olive though to rice bran oil.

No matter what style of food you cook you're bound to have a bottle of cooking oil lurking in the cupboard. Whether it's used to roast a tray of vegetables or make a tasty salad dressing, vegetable oil is a kitchen staple.

The reason there are so many different types of oils is because they can be extracted from a wide range of seeds, nuts, legumes, plant fruits and grains. E.g. sunflower seeds, walnuts, soybeans, olives and grains like rice can all be used to produce vegetable oils.

What are the healthiest oils?

Not all oils are created equal. Importantly, each oil can vary in the type and ratio of different fats that they contain. 

The healthiest oils are those which mostly contain heart-healthy poly- and mono-unsaturated fats.  Foods which are rich in these heart-healthy fats like nuts, seeds, avocado, olives and vegetable oils help to reduce levels of harmful cholesterol (low density lipoprotein - LDL) in the blood.  

In comparison, palm oil and coconut oil are high in saturated fat which increases LDL cholesterol and risk of heart disease. In recent years, coconut oil has become more popular and although using small amounts to add flavour is ok, it's a good idea to choose another oil like olive oil as a main cooking oil.

How are oils produced?

'Cold-pressing' is when the oil is extracted without any heat and is used to produce oils like extra virgin olive oil and avocado oil. 'Hot-pressing' is similar but the oil is extracted with heat and pressure. These processing techniques result in a less-processed oil which is higher in antioxidants with most of the flavour and colour retained. Although these oils are nutritionally better, they are also more expensive because they are costly to produce.

‘Refined oils’ are extracted using a solvent which is then followed by a refining, bleaching and deodorising process₁. These steps reduce the flavour, odour and colour of the original oil and also partially remove some of the antioxidants. These oils are usually cheaper and are often more stable at higher temperatures. Many of the oils on supermarket shelves are refined oils like soya bean, canola, rice bran and grapeseed oils.

What are the best oils to cook with?

High temperature cooking methods (like frying and deep-frying) can cause the oil to break down and produce chemicals like peroxides and aldehydes which are potentially harmful to our health.

Oils that are rich in polyunsaturated fats like flaxseed oil and sunflower oil (see table above) are particularly unstable when heated at high temperatures. Therefore, when shallow frying, barbequing or stir-frying at home, it is best to use an oil that is lower in polyunsaturated fat and saturated fat. The best choices from a nutrition, affordability and availability perspective are olive, rice bran and canola oils.

You can be a lot more flexible with the type of oil you use for salad dressings, sauces or for drizzling over pasta because the oil isn't being heated. Good choices include olive oil, flaxseed oil, sesame oil and avocado oil – choose an oil that you can afford and like the taste of, for these dishes.

Look after your oils

All oils will deteriorate over time with exposure to light, heat and air. The good news is there are lots of ways you can prevent and minimise damage to your oil₂.

Seven ways to get the most out of your vegetable oil:

1. Avoid stock-piling oil. Keep an eye on the 'use by' date and ideally use within 12 months.

2. Oils prefer cool, dark places. Where possible choose oil in a dark glass bottle or tin and store it away from direct light.

3. Use the right oil for higher heat cooking. Olive, canola and rice bran oils are all good choices.

4. Avoid overheating oil when cooking. When an oil is over-heated it produces unwanted chemicals. An oil's smoke point is the point at which the oil starts burning and smoking, which signals that damage to the oil has started.

5. Avoid reusing heated oils. As the oil darkens it develops off-flavours and becomes rancid.

6. Avoid deep-fried foods. If you do need to deep fry, corn and sunflower oils are unstable at high temperatures. Refined olive oil (light olive oil) and rice bran oils are better choices.

Take home points

The best sources of heart-healthy poly- and mono-unsaturated fats are from whole foods that are close to how they are found in nature like nuts, seeds, avocado, olives and oily fish.

When vegetable oils are used sparingly, they can be included as part of a heart-healthy diet alongside plenty of vegetables, fruit, nuts, seeds, legumes and whole grains. We recommend choosing the right oil for your budget and taking good care of it to prevent damage.

1. O’Brien R. Edible Fats and Oils Processing and Applications. In: Handbook of Food Science, Technology, and Engineering, Volume Four. ; 2005. doi:doi:10.1201/9781420026337.ch155

2. Choe E, Min DB. Mechanisms and factors for edible oil oxidation. Crit Rev Food Sci Food Saf. 2006;5:169-186.

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Dave Monro, NZRD

Chief Advisor Food & Nutrition

I completed chef training while studying nutrition/ dietetics and enjoy combining both of these elements to develop practical solutions for families to eat healthier.