Are all cooking oils the same, or are some preferred for different kitchen tasks, like frying? And is frying healthy?

Gustavo Bizon, Buenos Aires, Argentina

Dear Gustavo,

Most of us will, from time to time, eat deep-fried foods. We've all heard that too many fried things are not good for our health, and nutritionists warn us that only 10% of our calorie intake should come from fats.

At my cooking classes I usually include a few deep-fried dishes to highlight the versatility of a vegetarian diet. Apart from the question of calories, the two most common questions that I am asked about frying are these: Is frying in oil bad for the health, and do foods cooked in it have a bad effect on the organs?

I explain that all deep-frying is not equal, and that there are three factors to consider when answering these questions - (1) the type and characteristics of the oil used,
(2) the temperature, and (3) the time factor.

(1) The type and characteristics of the oil

• Peanut oil is good if you want to fry every day with the same oil, but only if you want to use it a few hours per day. Peanut oil can be strongly contaminated with aflotoxins, cancer-producing by-products of mold fungi.
  
• Sunflower oil is good if you fry the whole day continuously with the same oil. But then it should be replaced.
  
• Coconut fat is good for frying if it is not hardened. Hardened fats and oils are extremely dangerous to the health and should be avoided.
  
• Ghee or clarified butter is good for frying, but it is not commonly used in the food industry because it is more expensive than plant oils. It is highly recommended in India's classic Ayur Veda. Click here for more on ghee.

The main thing to remember is that none of these frying oils should ever be allowed to smoke. If this happens, the oil should be replaced with fresh oil. The reason for this is explained as follows.

(2) The temperature

There is a smoking point for every type of oil. For most frying oils, this temperature is around 180 - 190 degrees C. Shortly before smoking point, the oil starts to decompose, and the formation of free radicals and metabolites takes place. These substances are highly toxic and have been definitely linked with cancer. Further, this oil is cannot be properly digested by the liver and will lead to liver problems and a reduction of digestive ability if consumed regularly.

Some oils should never be heated at all, like oils containing polyunsaturated fatty acids. This also includes most cold-pressed, unrefined oils, safflower oil, nut oils, wheat germ oil, and linseed oil. Olive oil contains mainly mono-unsaturated fatty acids and it performs better if used for pan-frying rather than deep-frying.

Experienced cooks should be able to keep the temperature of oil at a constant level. If you are having difficulties in this regard, invest in a cooking thermometer, or use a deep-frying device with a thermostat.

(2) The time factor

The hotter an oil gets, the faster oxidation and decomposition takes place. And the longer you use an oil the more it oxidizes. Between two frying sessions, oils should be stored cool and light protected to slow down oxidation. If food particles remain in the oil during frying, they tend to burn and cause a rapid deterioration of the oil.

Test strips to measure oxidation are available at well-stocked kitchen suppliers. Keep all these points in mind for healthy, trouble-free frying.

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