How Much Trans Fat is Produced when you Heat Extra Virgin Olive Oil?

Some Background

All edible fats primarily comprise of fat molecules which in turn are made up of fatty acids. The fatty acids are made up of chains of carbon atoms that are held together mostly by single chemical bonds. But every now and then a double bond appears on the chain. The majority of the fatty acids in olive oil (typically 75%+) contain only one double bond, whilst the fatty acids that dominate most other edible oils contain a higher number of double bonds.

The double bonds in fatty acids allow them to be ‘kinked’. Normally they kink in one particular direction (known as the cis form). Upon heating however, a small proportion of these fatty acids kink in the opposite direction (known as the trans form) as the latter form is the most chemically stable. Our bodies have evolved to be able to use the cis type of fat for normal bodily functions, but not the trans type, the consequence being that consumption of the trans form results in cardiovascular disease.

What’s Been Done

A number of scientific studies have looked at the amount of trans fat formation in edible oils during heating. However, most used either temperatures way above those needed to fry, or the oil was heated for lengths of time that you would only use if you accidentally left oil on the stove before heading out for a vacation. These studies were conducted to replicate the type and length of heating used in commercial deep frying operations.

What’s Been Found

I have included all the studies where the temperature was kept to a recommended frying temperature 180-200C and where there was no possibility of the food that was being fried (if that was the case) contained trans fats themselves. Unfortunately, in all the studies excepting one, the length of time that the oil was heated for far exceeded a typical domestic frying time. However, the data they provided do allow estimates of how much trans fat is formed when cooking for shorter periods of time that are more typical of domestic frying.

Not many of these studies used EVOO as it is an oil that is rarely if ever used for continuous deep fat frying in a commercial environment (comparing how fats perform when heated for long periods of time as occurs in commercial fat frying operations is the purpose of most studies, as the results have big $ implications). However, the same basic chemistry of isomerisation apply to all oils, so I have also summarised the results from these.

Results More here

Source :  Slick Extra Virgin, by Richard Gawel