Cooking with oil: what you need to know

One of the most confusing aspects of healthy eating is knowing which oils are best to cook with. Many commercial diet plans advocate ‘low fat’, but what does that mean in terms of which oils to use in which dishes, and when? In this post I set the record straight in terms of why some oils should be used in hot cooking and some should be avoided, and only used cold.

The science bit

In simple terms, every oil has a ‘smoke point’ when heated, each oil reaching this point at a different temperature. It’s using oil at it’s individual  smoke point or even hotter which runs the risk of creating heat-induced damage. The oils you choose to cook with must be stable enough to resist chemical changes when heated to high temperatures, or you run the risk of damaging your health.

The health risks of heating vegetable and seed oils

Heating up vegetable oils leads to the release of high concentrations of aldehydes, which can cause inflammation – and increasingly, inflammation is being linked to our modern world diseases of cancer, arthritis, Parkinson’s and Alzheimer’s.

Another way vegetable oils can inflict damage is by converting your good cholesterol into bad cholesterol—by oxidising it. When you cook with polyunsaturated vegetable oils (e.g. corn, soy or seed oils such as sunflower or rapeseed), oxidised cholesterol is introduced into your system, because as the oil is heated and mixes with oxygen, it becomes oxidised and goes rancid, creating free radicals.

Another important factor is that most vegetable oils are high in omega-6 fats and it is the ratio of omega-3 to omega-6 fats that plays a powerful role in determining many illnesses. So if you are consuming large amounts of Omega 6-rich seed oils you will seriously distort this vital ratio and increase your risk of many degenerative diseases.

Changing attitudes to cooking with oil

The field of nutrition is an evolving science. As ‘a person in charge of a body’, we need to keep ourselves updated with regards to what’s the best way to nourish ourselves.

Yes, nutritionists have been recommending that we use vegetable or sunflower oil for cooking over the last decades but the latest research shows oils such as sunflower oil and corn oil produce aldehydes at levels 20 times higher than recommended by the World Health Organisation.

Increasingly, people are beginning to understand that the food scientists who scared us away from cooking with certain fats got it wrong. Just cook as our grandparents generation did using animal fat, butter, ghee or coconut oil – look at any countries’ traditional diet and follow what they did before the chemical extraction of seed oils was even possible.

Which oils to heat

Contrary to the dietary advice we’ve been given for the last few decades, it is now recommended that people use coconut oil or ghee for frying or cooking because lower levels of toxic chemicals are generated, and secondly the chemicals which are formed are less threatening to the human body.

Oils such as Olive oil, butter and goose fat produce far fewer harmful chemicals.


Seed oils contain many nutritional benefits but those deteriorate when subjected to heat.

Keeping A Range of Oils

The best strategy for cooking with oil is to stock a range in your larder:

  • Keep coconut or a similar saturated fat for heavy frying,
  • Light olive oil and ghee for light frying,
  • Pumpkin, avocado and extra-virgin olive oil for dressings, dips and salads.
  • Flax seed oil is an excellent choice for a cold oil as it is full of Omega 3 fatty acids.