Which Oils Are Best For Cooking?

olive oil

Which fats and oils do you use in the kitchen? You may decide to switch to olive oil, rapeseed oil or coconut oil after learning the latest research findings. When you cook with fats and oils, heat changes their molecular structure to generate toxic chemicals called aldehydes. These are linked with an increased risk of heart disease and cancer so you obviously want to eat as few of them as possible. But when a BBC2 Panorama documentary analysed the cooking residues from a variety of oils and fats, they found some astonishing results. Heating olive oil, cold-pressed rapeseed oil, butter, goose fat and lard produced the fewest aldehydes while the levels generated by cooking with sunflower oil and corn oil were 20 times higher than World Health Organisation recommended limits.

Other researchers have found that safflower oil also produces high levels of aldehydes, as shown the graph below.

In comparison, heating rapeseed/canola oil and coconut oils produce relatively low levels up to 210 degrees. The ‘best’ oil which produces the lowest level of aldehydes even at very high temperatures, appears to be coconut oil whose saturated fat content makes it particularly stable.

Omega-6s versus Omega-3s

Sunflower, safflower and corn oils are rich in omega-6 polyunsaturated fats, whose double bonds are highly reactive and generate other chemicals more easily.  In contrast, olive oil, rapeseed oil and animal fats are rich in monounsaturated and saturated fats which are relatively stable when heated. And, as well as generating lower levels of aldehydes, those that do form are less harmful to health. This is why the Panorama researchers suggested that olive oil was best for cooking and frying. They added that sunflower and corn oil are fine to use in salad dressings as long as you don’t heat them. But, given that olive oil and rapeseed oils are perfectly good for salad dressings, too, my advice is to ditch the sunflower and corn oils altogether, and here’s why…

Sunflower, corn and safflower oils are often promoted as ‘healthy’ because they are rich in polyunsaturates, but these are mainly in the form of omega-6s which promote inflammation in the body, not omega-3s which help to neutralise inflammation.

Humans evolved on a Stone Age, hunter-gatherer diet of green plants, wild animals and fish which provided a low ratio of omega-6s (from natural vegetable oils) and omega-3s (from oily fish) of around 2:1. In a typical Western diet, the ratio of inflammatory omega-6s to non-inflammatory omega-3s is closer to 10:1 and often higher. This is one popular reason to help explain why inflammatory conditions such as asthma, eczema and arthritis are becoming more common.

Because we can’t convert excess omega-6s into omega-3s (or vice versa) it’s important to obtain a balanced dietary intake of both types of polyunsaturated fatty acid to limit the level of inflammatory mediators we produce.

Olive oil is good in this respect as it consists of around 75% healthy monounsaturated fat, 15% saturated fat with only 9% omega 6s (although most of these are omega-6s). Like olive oil, rapeseed oil is high in monounsaturated fat (60%) and its ratio of omega-6s to omega-3s is an optimal 2:1.

The ratio of omega-6s to omega-3s in sunflower oil is 9:1, for safflower oil it’s at least 75:1, and for corn oil the ratio is 56:1. If you are interested, there’s a good diagram showing the composition of various fats and oils HERE.

Although intakes of these oils should be viewed in relation to the diet as a whole, this is another good reason, in addition to the aldehyde story, to limit your intakes of these supposedly ‘healthy’ fats in favour of olive, rapeseed and coconut oils.

Cooking with olive oil

Extra Virgin olive oil from the first pressing of the fruit has the highest antioxidant content and freshest flavour. This is ideal for dips, drizzling on food, salad dressings and for gentle braising (below 180°C). Above this temperature, the green colourants start to smoke so for high temperature cooking I use pure olive oil which is a blend of refined and virgin olive oils. These are more resistant to high temperatures and can be heated to 210°C without generating smoke and off flavours.

Which fats and oils do you use in the kitchen? Is this based on health, taste or just habit? I’m fascinated by how different fats go in and out of fashion – even the butter versus margarine debate has now turned full circle and butter is no longer as demonised. In fact, sugar is the new enemy and for all the right reasons.

Image credits: pixabay;

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Dr Sarah Brewer
QUORA EXPERT - TOP WRITER 2018 Dr Sarah Brewer MSc (Nutr Med), MA (Cantab), MB, BChir, RNutr, MBANT, CNHC Cert IoD qualified from Cambridge University with degrees in Natural Sciences, Medicine and Surgery. After working in general practice, she gained a master's degree in nutritional medicine from the University of Surrey. Sarah is a registered Medical Doctor, a registered Nutritionist and a registered Nutritional Therapist. She is an award winning author of over 70 popular self-help books and a columnist for Prima magazine.

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