Budding chefs eager to cook up healthy meals for friends and family face a barrage of conflicting advice.
There are advocates of the raw food diet, who abhor the thought of cooking.
And then there are those who believe black pudding to be the latest superfood.
But, now a team of Spanish scientists have added a new theory to the mix.
They suggest frying vegetables is a healthier alternative to boiling – as long as the cook is using extra virgin olive oil.
Their study found the cooking method increases the antioxidant capacity and phenolic fraction present in raw vegetables typical of a Mediterranean diet.
These compounds, the researchers said, help prevent chronic diseases including cancer, diabetes and macular degeneration.
A new study, by scientists in Spain, has found frying vegetables in extra virgin olive oil is healthier than boiling them. Researchers found the oil increases the levels of cancer-fighting antioxidants, and phenols, also linked to preventing chronic diseases, including cancer, diabetes and macular degeneration
Professor Cristina Samaniego Sánchez from the University of Granada, said: ‘Oil increases the amount of phenolic compounds in vegetables, which is the opposite to boiling.
‘Therefore, we must stress that frying and sautéing conserve and enhance the phenolic composition.’
The Mediterranean diet is characterized by a high intake of vegetables and extra virgin olive oil.
These are both an important source of dietary phenols – compounds linked to the prevention of chronic diseases.
This kind of antioxidants can be modified during the cooking process, increasing or decreasing their concentrations.
The researchers set out to discover whether the choice of cooking medium – olive oil, water, or a mixture of both – had any effect on the amount of these helpful compounds in the cooked food.
They conducted an experiment, cooking 120 grams of potato cubes, pumpkin, tomato and eggplant – all without seeds or skin.
They used three cooking methods – frying, boiling and cooking with a mix of extra virgin olive oil and water.
In the laboratory, the samples were tested by high-performance liquid chromatography to measure levels of moisture, fat, dry matter and the total number of phenols, as well as the measurement of antioxidant capacity.
Their results revealed that using extra virgin olive oil for frying vegetables increases their fat content and reduces their moisture, while this was not observed in other cooking methods.
The scientists said the extra virgin olive oil increases the level of phenols in the vegetables, because they are transferred from the oil to the vegetables during the cooking process. They did warn the cooking process does increase the vegetables’ ‘energy density’ – or calorie content
Professor Samaniego said: ‘Comparing the content of phenols with that of raw vegetables we found increases and reductions alike, depending on the chosen method.
‘Oil as a mean of heat transfer increases the amount of phenolic compounds in vegetables, opposite to other cooking methods such as boiling, where heat transfer is done through water.’
She said the extra virgin olive oil transfers phenols to the vegetables, adding those which are not present in raw vegetables.
‘Therefore, we can confirm that frying is the method that produces the greatest associated increases in the phenolic fraction, which means an improvement in the cooking process although it increases the energy density by means of the absorbed oil,’ Professor Samaniego said.
In other words, Professor Samaniego warned, frying increased the number of calories in the food, as well.
All the cooking methods increased the antioxidant capacity of all four vegetables, but boiling is only recommended when both the vegetables and the cooking water are to be consumed, Professor Sánchez adds.
The article was published in the journal Food Chemistry.