Oxidized oils in food may be harmful to health

Judy Thalheimer, RD, LDN
Environmental Nutrition

You've probably heard that mono- and polyunsaturated fats, like those in olive oil, nuts, and fish, are a heart-healthy choice, but concern is rising that, if not stored and used properly, these foods and oils actually could be bad for your body.

When one molecule gives up an electron to another, scientists say it is "oxidized." Oxidation happens through chemical reactions in our bodies all the time. The process creates "free radicals," which can cause damage that raises our risk for heart attack, stroke, cancer and other problems. But oxidation happens outside of our bodies as well. That rust on your car is oxidized metal. And that telltale paint-like odor wafting from an old box of crackers or the bottle of cooking oil you keep by the stove is oxidized fat. Can oxidized fats we eat cause the same damage as free radicals formed inside our bodies?

Some researchers believe that certain end-products of oxidation are not absorbed by the body, and that we likely don't eat enough to cause a significant problem. But a number of experiments that fed oxidized vegetable oils to animals showed they can cause damage to brain cells, lead to inflammation, and increase the risk of diabetes and cardiovascular disease. If these results hold true in humans, regularly eating oxidized oils could be a threat to our health.

What to do? There's plenty you can do to protect yourself from the possible ill effects of consuming oxidized fats. The simplest approach is to limit deep-fried foods and avoid eating any food that has an unpleasant rancid smell or taste. Foods at risk for becoming rancid include vegetable or fish oils, whole grain products, nuts and nut oils, seeds, and anything made with these ingredients. If you use and store these healthy, nutrient-rich foods properly, there is no need to worry about oxidative damage. For added insurance, eat plenty of fruits and vegetables, which have loads of antioxidants to neutralize those oxidized fats.

Slow Down Oxidation

Air, heat and light speed up oxidation. Here are some tips for slowing it down.

■Limit deep-fried foods and don't reuse cooking oil.

■Store cooking oil, whole-grain flours and nuts in cool, dark places.

■Refrigerate polyunsaturated oils, especially fish, nut and flaxseed oils.

■Choose oils packed in tinted glass containers, or wrap clear bottles in foil.

■Pick oil bottles from the back of the market shelves where it's darker.

■Re-cap oils right after pouring, and don't store by the stove.

■Check expiration dates carefully. Since most shelf-stable trans fats have been replaced with healthier but more oxidation-prone fats, don't expect processed foods to last as long as they used to.

■Try whole, raw nuts (naturally rich in oils), which maintain freshness longer than roasted, chopped and ground nuts.

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