Fruits and vegetables that can protect against cancer

Originally Published: June 28, 2002 - Last Updated / Reviewed On: January 31, 2013
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Dear Alice,

As a cancer survivor, I am looking for ways to keep my body healthy. What fruits and vegetables are high in antioxidants?

—Jill

Dear Jill,

You're right in thinking that some foods could help improve health or protect against disease. Some of these disease-fighting substances in food are vitamins and minerals, but another diverse group of plant chemicals are called phytochemicals. Phytochemicals, many of which are antioxidants, impart distinct flavors, aromas, and pigments to foods. For example, one enormous class of antioxidants, flavonoids, includes a group called allyl sulfides, which are found in garlic, onions, and shallots. It's believed that allyl sulfides may help produce a detoxification enzyme that protects against carcinogens. Other antioxidants are detectable by their colors — vividly colored fruits and veggies are rich sources of beneficial plant chemicals. For example, anthocyanins are antioxidants that lend the deep red, blue, and purple hues to raspberries, blueberries, eggplant, and red cabbage.

So how do antioxidants work? They are believed to protect cells from "free radicals," which are harmful oxygen molecules. Free radicals may cause damage to cells, possibly resulting in cancer. Smoking, air pollution, infection, and excessive sunlight can all increase production of free radicals, although they are also formed from normal bodily functions. Antioxidants may help prevent the formation of carcinogens (cancer causing substances), block the actions of carcinogens, and/or suppress cancer development. Most of these actions have yet to be proven in humans; however, foods containing antioxidants (mostly plants) contain many other healthy components.

The following table lists various classes of antioxidants and other phytochemicals, some of their rich food sources, and how they are believed to work:

Substance

Food Sources

Possible Action(s)

Vitamin C

citrus fruits, tomatoes, peppers, broccoli, leafy vegetables, strawberries, potatoes

Inhibits nitrosamine formation, a potentially dangerous carcinogen

Carotenoids

apricots, papaya, sweet potatoes, tomatoes, mangoes, carrots, pumpkin, red peppers, spinach, corn, cantaloupe

Numerous anti-cancer functions

D-limonene

citrus fruits

May detoxify cancer promoters

Lycopene

cooked tomato products, watermelon, pink grapefruit

A class of carotenoids that's protective against prostate and possibly other cancers

Anthocyanins

blueberries, strawberries, raspberries, blackberries, grapes, cherries, red peppers, eggplant, red cabbage

Antioxidant cell protection; may help prevent binding of carcinogens to DNA

Allyl sulfides

garlic, onions, shallots, leeks, chives, scallions

Various anti-carcinogen functions

Monoterpenes

parsley, carrots, broccoli, cabbage, cucumbers, squash, eggplant, peppers, mint, basil, citrus fruits

Aid protective enzyme activity

Flavonoids

parsley, carrots, citrus fruits, broccoli, cabbage, cucumbers, squash, tomatoes, eggplant, peppers, soybeans, berries

Block receptor sites for hormones that promote cancer

Indoles

cabbage, Brussels sprouts, kale

Stimulate production of enzymes that break down cancer causing agents

Phenolic acids

parsley, carrots, broccoli, cabbage, tomatoes, eggplant, peppers, citrus fruits, whole grains, berries

Antioxidant properties; inhibit nitrosamine formation and help form protective enzymes

Catechins

green tea, berries

Antioxidants linked to lower rates of gastrointestinal cancer

As you can see, a wide variety of fruits and veggies fall into one or more of the categories named above. Of note, the benefit from phytochemicals comes from eating the food, not in taking pills or supplements. Fruits and veggies contain a variety of phytochemicals, vitamins, and minerals, as well as fiber — these cannot be replicated in a pill form. In addition, excessive amounts of certain vitamins or other compounds found in some supplements have the potential to cause harm.

For tips on how to pack plenty of fruits and vegetables into your diet, check out The Get Balanced! Guide to Healthier Eating. This tool that has been developed specifically for Columbia students. You may also want to check out the Optimal Nutrition section of the Go Ask Alice! archives.

To optimize your antioxidant intake, you can include at least five servings of fruits and veggies a day. If you're already doing this, why not aim for even more? Researchers have found that five to nine servings per day are most beneficial. Set your sights on variety, too. To obtain the benefits of these plant compounds, try to vary your selections from day to day, and from week to week. Include red, yellow, green, orange, blue, purple, brown, and white fruits and veggies, and enjoy a colorful (and healthful) eating plan!

Alice