Anna Hartz
Can rancid oil harm your health? Scientists explain
Fat is an large part of our diet. According to Norway’s Directorate of Health, about one-third of the calories we consume come from fat. It can come from animals or plants, and every type of fat can eventually go bad.
Different types of fat
Many people notice spoiled fat right away because it develops an unpleasant smell and taste. Some people compare the smell to paint or turpentine, while others say it reminds them of dry grass.
Astrid Nilsson from the Norwegian research institute Nofima studies fats, food quality and how they affect flavor and shelf life, writes Videnskab.
Fat is made up of different fatty acids. The structure of these fatty acids determines whether the fat is saturated or unsaturated. Saturated fats are commonly found in butter, cheese, milk and meat. Coconut oil and palm oil also contain saturated fat.
Unsaturated fats are found in plant oils, nuts, seeds and oily fish. These fats react more easily with oxygen. When that happens, a chemical process begins. The fat breaks down into smaller compounds that create the familiar rancid smell and taste.
Nilsson says some compounds produced during this process have no smell at all. Some studies suggest that certain odorless compounds may be harmful. She says the unpleasant smell of rancid food may actually help protect us because it warns us not to eat it.
Oxidized fats
Air enters an oil bottle as soon as it is opened. Every time the bottle is used, more oxygen gets inside. Light and heat also speed up the process.
That is why experts recommend storing oils in a cool and dark place. Nilsson says the refrigerator is the best option. Olive oil may become solid when chilled, but it quickly returns to normal at room temperature.
Butter and margarine are better protected because only the surface is exposed to air. If a yellow layer appears, Nilsson simply scrapes it off. She says small amounts are not dangerous.
Research has shown that human cells can handle a certain amount of oxidized fat. In one study, healthy volunteers took rancid fish oil capsules for eight weeks. Blood tests showed no harmful effects.
Nilsson still recommends checking fish oil capsules from time to time. She also advises eating colorful fruits, vegetables and berries because they provide antioxidants that help protect the body.
