Explainer: What Are Antioxidants?

Certain chemicals, including many in foods, protect the body from harmful chemical reactions

Here’s a rainbow of carrots that U.S. scientists have developed to be both nutritious and a good source of natural antioxidants. 

Stephen Ausmus/USDA-ARS

Antioxidants are chemicals that may help fight damage due to disease and aging. These powerful compounds work by blocking what’s known as oxidation. That’s a type of natural chemical reaction (often involving oxygen). And this reaction can harm cells.

The molecules that trigger oxidation are called oxidants. Chemists tend to also refer to these as free radicals (or sometimes just “radicals”). They are produced by nearly everything we do that involves oxygen. That includes breathing and digestion.

Free radicals aren’t all bad. They perform important roles in the body. Among those good tasks: killing off old cells and germs. Free radicals become a problem only when we produce too many of them. Cigarette smoke exposes the body to free radicals. So does other types of air pollution. Aging does too.

To keep oxidation from harming healthy cells, many plants and animals (including people) produce antioxidants. But the body tends to make fewer of these helpful chemicals as it gets older. That’s one reason scientists suspect that oxidation is related to the types of chronic diseases seen in senior citizens. These include heart ails, diabetes and more.

Plants make hundreds of thousands of chemicals. These are known as phytochemicals. Many thousands of these work as antioxidants. Scientists now think that eating a wide variety of plant-based foods containing these compounds can boost antioxidant defenses in people. This could keep us healthier and less prone to disease.

In fact, that’s one reason why experts recommend that people eat many different fruits and vegetables. Which foods are richest in these chemicals? One clue is color. Many plant pigments are powerful natural antioxidants. Plant-based foods that are bright yellow, red, orange, purple and blue often contain good sources of these pigments.

Not all antioxidants are pigments, however. So the best policy is to eat plenty of plant-based foods every day. Below are some examples of potent antioxidants that can be found in fruits and vegetables:

vitamin C (or ascorbic acid) — oranges, tangerines, sweet peppers, strawberries, potatoes, broccoli, kiwi fruit

vitamin E— seeds, nuts, peanut butter, wheat germ, avocado

beta carotene(a form of Vitamin A) — carrots, sweet potatoes, broccoli, red peppers, apricots, cantaloupe, mangoes, pumpkin, spinach

anthocyanin— eggplant, grapes, berries

lycopene— tomatoes, pink grapefruit, watermelon

lutein— broccoli, brussels sprouts, spinach, kale, corn

Janet Raloff is the editor of Science News for Students. Prior to this, she was an environmental reporter for Science News, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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