A research published in Food Chemistry, observes that frying in extra virgin olive oil is healthier than other cooking methods and can help to prevent cancer, diabetes or macular degeneration. Numerous studies have already proven the virtues of the Mediterranean diet. There is evidence that it leads to a lower risk of heart disease, stroke and other cardiovascular problems, improves gut health, slows the process of brain aging and reduces the risk of various chronic, degenerative conditions.

The Spanish Mediterranean diet features a high volume of vegetables and Extra Virgin Olive Oil (EVOO), both of which are good sources of phenols, the antioxidant effect of which is believed to contribute to the reduction of health risks. Concentrations of antioxidants can be either increased or decreased, depending on how the food is processed.

Researchers from the University of Granada in Spain wanted to compare cooking methods to find out which one would give the best antioxidant capacity, and maximize the amount of phenolic compounds provided by vegetables used in the Mediterranean diet, including potato, pumpkin, tomato and eggplant. Under controlled conditions, the team cooked 120 g of potato, pumpkin, tomato and eggplant without seeds or skin. They compared three methods: frying, boiling and cooking with a mixture of EVOO and water. The ratio of vegetable to water followed traditional Spanish cooking methods.

They also used high-performance liquid chromatography (HPLC) to measure the levels of phenolic compound in each vegetable. Frying in EVOO was found to increase fat content and reduce moisture; other methods did not have this effect. Cooking in oil increased the levels of phenolic compounds, but cooking in water did not. This is thought to be due to phenols being transferred from the EVOO to the vegetables, adding to the vegetables some beneficial compounds not normally found there.

Results showed that frying in EVOO is the most effective way to increase the antioxidant capacity and levels of phenolic compounds in raw potato, pumpkin, tomato and eggplant. In other words, the cooking process improves the quality of the raw foods. Any raw vegetable that started with a high level of phenols had its phenolic content boosted further by the use of EVOO in cooking, suggesting that frying and sautéing should be used not only to conserve the goodness, but also to enhance it.

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