Why is it bad to use the same cooking oil more than once?

There are a few reasons why it is not recommended to reuse cooking oil more than once.

1. Thermal Oxidation: When oil is heated to high temperatures, it undergoes a process called thermal oxidation. This causes the oil to break down and form harmful compounds, including aldehydes and ketones. These compounds can damage cells in the body and have been linked to an increased risk of chronic diseases such as cancer, heart disease, and diabetes.

2. Polymerization: Over time, oil can undergo polymerization, which is a process where individual molecules join together to form larger molecules. This can cause the oil to become thicker and more viscous, which can affect the taste and texture of food.

3. Free Radicals: When oil is heated, it produces free radicals, which are unstable molecules that can damage cells in the body. Free radicals are linked to an increased risk of chronic diseases such as cancer, heart disease, and aging.

4. Nutrient Loss: Reusing cooking oil can also lead to a loss of nutrients. This is because the nutrients in oil can be destroyed by heat and oxidation.

5. Smoke Point: The smoke point is the temperature at which oil begins to produce smoke. When oil is heated beyond its smoke point, it starts to break down and produce harmful compounds. Reusing oil can increase the risk of reaching the smoke point and producing these harmful compounds.

For these reasons, it is recommended to discard used cooking oil after each use.