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 oxidation. That’s a type of natural chemical reaction (often involving oxygen) that can harm cells.

The molecules that trigger oxidation are called, not surprisingly, oxidants. Chemists tend to also refer to these chemicals as free radicals (or sometimes just “radicals”). They are produced by nearly everything we do that involves oxygen, including breathing and digestion.

Free radicals aren’t all bad. In fact, they perform important functions 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. Breathing in cigarette smoke and other types of air pollution often increases the body’s exposure to free radicals. So does aging.

To keep oxidation from harming healthy cells, many plants and animals (including people) produce antioxidants. However, organisms tend to make fewer of these helpful chemicals as they get old. That’s one reason scientists suspect that oxidation is related to the types of chronic disease (heart ails, diabetes and more) seen in senior citizens. With fewer antioxidants to defend their bodies, oxidation can damage more and more of their cells.

Plants make hundreds of thousands of chemicals, also known as phytochemicals. Many thousands of these work as antioxidants in the human body. Scientists now think that eating a wide variety of plant-based foods containing these compounds can boost our own antioxidant defenses. This could keep people healthier and less likely to develop disease.

In fact, that’s one reason why experts recommend that people eat many different kinds of fruits and vegetables. Which foods are richest in these chemicals? One easy clue is color. A number of the plant pigments are powerful natural antioxidants. And 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 various fruits and vegetables:

vitamin C(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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