Niki Bezzant: Drill deep for truth on cooking oils

According to NZ's top expert in edible oils, polyunsaturated oils oxidise at high temperatures and release aldehydes chemicals that are not good for us. Photo / Getty Images

This week's alarming health headlines are about new research showing vegetable oils release toxic chemicals when heated, which cause cancer.

A Daily Telegraph story asserted this "threatens to turn on its head official advice that oils rich in polyunsaturated fats - such as corn oil and sunflower oil - are better for the health than the saturated fats in animal products".

Once again we have the "everything you have been told before is wrong" angle.

That is about as far as most of us will have gone in reading this story: the headline plus the few lines that show up in our Facebook feed.

However, unpacking this a bit - which took calls to oils experts, dietitians and the Heart Foundation - proved interesting.

First: this is not new. It has been known for more than 30 years, according to New Zealand's top expert in edible oils, Laurence Eyres, that polyunsaturated oils oxidise at high temperatures and release aldehydes - chemicals that are not good for us.

For this reason, it's not recommended to fry with highly unsaturated oils. In the New Zealand fast-food industry, sunflower or maize oils are not used for frying. Our fish and chips are probably not killing us with aldehydes.

They may, however, be killing us in other ways, and here is where we need to look at the bigger picture. No one should be eating lots of deep-fried food, no matter what it is fried in.

The fat in deep-fried foods tends to come with salt, sugar and refined carbohydrates in a high-kilojoule package that is probably worse, long term, than the toxic chemicals that may be in the oil.

If you eat lots of fried food, you have bigger worries.

When it comes to nutrition, it has also been known for some time that we need to get the balance of polyunsaturated fats in our diets right: a mix of omega-3 fats and omega-6 fats.

For most of us that means getting more omega-3s (found in oily fish, walnuts and flaxseeds).

What does this mean in our kitchens? A diet based on plants - full of colourful vegetables and fruit - and including nuts, seeds, avocados, olives and fish, provides a good range of nutrients and healthy fats from these whole-food sources.

On top of a good base like this, the oil you cook with - in moderate amounts - is up to your taste, recipe and budget. Eyres recommends fresh New Zealand-produced olive oil, which has low acidity and a high smoke point - for frying.

Canola oil is economical and useful for high-heat cooking. The Heart Foundation recommends rice bran oil and refined olive oil for stir-frying or shallow frying.

Avocado and macadamia oils are healthy and great for cooking and dressing.

A little bit of butter or coconut oil won't kill you, but don't believe the hype: butter is not suddenly a health food, and coconut oil doesn't cure Alzheimer's.

Niki Bezzant is editor-in-chief of Healthy Food Guide