For years now, we have all been told that certain fats are bad for us and should be minimalized. At the same time, we have been told that certain oils are a far better alternative and should be used for cooking. But the scientific opinion on this is changing and one study by the TV show Trust Me, I’m A Doctor has shown that cooking with so-called healthy oils may actually be less beneficial than the fats of old.
Study
The program conducted a study where they gave families a range of fats and oils and asked them to use them in their daily cooking. They also collected the leftovers for analysis. The products used included sunflower and vegetable oils, corn oil, cold pressed rapeseed oil, olive oil both refined and extra virgin, butter and goose fat. Samples were sent to the University of Leicester and provided some surprising results.
When you fry or cook at a high temperature, around 180 C or 350 F, the molecular structure of these substances undergoes a change called oxidation. This means they react with the oxygen in the air and form something called aldehydes and lipid peroxides. This does happen when they are kept at room temperature but at a much slower rate.
Aldehydes have been shown that when consumed or inhaled, even in small amounts, they have a connection with an increased risk of heart disease and cancer. What the study found was that the oils rich in polyunsaturated – namely the corn and sunflower oils – generated high levels of aldehydes. This is in contrast to the view of sunflower oil as being a ‘healthy’ option.
Heat issues
Both sunflower and corn oil are fine to use as long they aren’t heated such as when frying or cooking. When heated, a formerly healthy oil becomes unhealthy due to the chemical conversion that takes place.
Olive oil and rapeseed oil produced far less aldehydes as did both the goose fat and the butter. The reason for this is that they are higher in monounsaturated and saturated fatty acids, both of which are more stable when heated. Saturated fats show barely any reaction at all when used for frying or cooking.
Prof Martin Grootveld, who studied the results for the show, said that he would recommend olive oil for cooking. This is for two reasons – one because of the lower levels of toxic compounds generated and two because the ones that are formed are less dangerous to the human body. Despite its bad reputation, lard is actually rich in monounsaturated fats.
Compromise
So the overall advice based on the findings included do less frying, particularly at high temperature. If you need to fry at a high level, then minimalize the amount of oil used and remove it from the outside after cooking with kitchen towel.
To reduce aldehyde production, go for products high in monounsaturated or saturated fats and low in polyunsaturated fats. This leads to olive oil coming out as the ideal compromise as it is 76% monounsaturated, 14% saturates and just 10% polyunsaturated. Finally, always keep oils in the cupboard and don’t reuse them after cooking as these increases the nasty side effects.
