Should you eat foods prepared in previously heated cooking oil

It is not recommend to reuse the cooking oils or eat foods that are cooked in oils that have been reheated, whether you’re dining at home or in restaurants….and here’s why.

Researchers from the University of the Basque Country (UPV/EHU, Spain) were the first to discover the presence of certain aldehydes in food, which are believed to cause some nerve-related diseases and cancer.

Aldehydes can be found in some oils, such as sunflower oil, when heated at a suitable temperature for frying.

‘It was known that at frying temperature, oil releases aldehydes that pollute the atmosphere and can be inhaled, so we decided to research into whether these remain in the oil after they are heated, and they do’, María Dolores Guillén, a lecturer in the Pharmacy and Food Technology Department at the UPV, said.

‘It is not intended to alarm the population, but this data is what it is, and it should be taken into account,’ Guillén highlights, who points out the need to continue researching to establish clear limits regarding the risk of these compounds.

‘On some occasions the dose makes the poison,’ Guillén reminds us.

In another study it was found that a toxin called 4-hydroxy-trans-2-nonenal (HNE) forms when oils such as canola, corn, soybean and sunflower oils are reheated.

Foods that contain HNE from cooking oils have been associated with increased risks of cardiovascular disease, stroke, Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, liver disorders, and cancer.

HNE after being absorbed in the body reacts with DNA, RNA and proteins affecting basic cellular processes.

A study presented at the American Oil Chemists Society meeting in May 2005 found that HNE is seen in oils that are reheated in homes for cooking a day or two after they were originally used.

The researchers at the University of Minnesota recommend avoiding foods fried made in polyunsaturated vegetable oils (sunflower, soybean, canola, corn oil) at home and in restaurants.

It is worrisome to know about reheated cooking oils used in restaurants rather than at home because foods cooked at home generally don’t use as much oil as restaurants do and probably don’t reuse the oil as much.

Restaurants, on the other hand, do not follow industry standards that specify what kinds of cooking oils are best to use or how many times the oils can be reheated. Cooking oils are also expensive and so it is economical for restaurants to reuse them.

Corporations providing meals to employees should take efforts to find out how the caterer who is supplying the meals is cooking – especially any deep-fried food items that are in the menu.

Ideally, never eat anything deep-fried in a restaurant, unless the restaurant guys are kind enough to show the oil they are using, that it is new and the cooking utensil is clean too….and that is very unlikely.

As aldehydes remain in the oil after they are heated, using a previously heated oil will have an increased concentration of the aldehyde – never reheat the leftover oil to make your meal…you are inviting some serious diseases.

Lastly, whether to reuse oil for cooking and if yes, how many times, is still a controversial subject and an individual decision as well. Initial research, however, suggests to avoid it. However, if planning to reuse the oil, strain it properly to remove the crumbs or food pieces floating in it, and store it in a tightly-sealed separate container in a dark, cool place. This is because the big enemies of oil are humidity, heat and light. Also before or while cooking or frying check if the oil is foamy or smelling rancid – if yes, discard it.