Heated cooking oils and cancer

 

Web based sites see a deluge of mail from persons concerned about developing cancer from frying with olive oil. It is unknown where this common food myth comes from but this sort of misinformation seems to spread like a computer virus. Perhaps it was the finding of contaminants in Spanish refined olive oil (fraudulent oil) in early 2001 which prompted the concerns. Or perhaps it is based on the production of certain chemicals in oils either in the natural state or when they are severely heat abused. If we review the chemical basis for these myths we often see a kernel of rationality but the facts get blown out of all proportion by people who cannot apply logic or scientific inspection to chemical analyses.

 

 

Polycyclic aromatic hydrocarbons are a group of chemicals which are formed when petroleum, petroleum products, coal, wood, cellulose, corn, or oil are burned. There are over 100 PAHs which have been studied. During oxidation and detoxification in the liver they are thought to form substances which damage DNA, starting a chain of events which could lead to cancer. A few of them have been classified by the EPA and The Department of Health and Human Services as carcinogenic to animals in studies and probably carcinogenic to humans.

A person's exposure at home to PAHs would likely be through tobacco smoke, wood smoke, vehicle exhausts, asphalt roads, coal, coal tar, wildfires, agricultural burning, waste incineration, creosote-treated wood products, cereals, grains, flour, bread, vegetables, fruits, meat, processed or pickled foods.

 

Twenty years ago there was a food scare when PAHs were first being researched. They were found in meat and other foods which had been cooked at high temperatures, such as grilling and charring. The American Institute for Cancer Research recommends avoiding charring meat when grilling, pre-marinade, which somehow minimizes PAH formation, and minimizing the amount of grilled meats consumed. (Grilled vegetables or fruit do not form PAHs).

 

Many foods naturally contain small quantities of PAHs. Olive oil, like other vegetable cooking oils, has been found to contain minute amounts of up to 17 PAHs such as benzanthracene and chrysene. Unripe olives tended to have more than ripe olives.

 

Burning any cooking oil can increase the amounts of PAHs. Oil of any kind which has been repeatedly heated to its smoking point will lose its natural antioxidants and begin to accumulate free radicals and other cancer causing substances. Whether this has actually caused cancer in humans has never been proven. Commercial industrial kitchens which fry foods repeatedly would be where this sort of thing might happen. It is unlikely that you would repeatedly fry at continuous high temperatures with the same oil at home. In commercial operations the oil is examined regularly with a rancidity test and discarded before it gets to a dangerous stage. Olive oil is typically not used in commercial kitchens as it is much too expensive. Cheaper oils like canola, corn or peanut oil are used instead. Extra virgin olive oil has more natural antioxidants which soak up free radicals. So heating it would produce fewer free radicals than a lower grade olive oil. It is most unlikely that in home use olive oil or other cooking oils would be a significant source of PAHs.