Antioxidants are nutrients from food that may protect the body against the damaging effects of free radicals, molecules that can damage cells, and may play a role in heart disease, cancer and other diseases, such as asthma and Alzheimer's. There are many different types of antioxidant compounds which can be broken down into two categories: flavonoids and nonflavonoids.

Flavonoids

Flavonoids are a group of antioxidant compounds found primarily in plants. They are primarily known as pigments for flower coloration, producing yellow or red/blue pigmentation in the flower petals. There have been over 4,000 identified, and can be sub-divided into seven groups:

• Anthocyanidins - This group is commonly found in red and blue colored foods, such as berries, grapes and red wine. They may help to keep blood vessels healthy.
• Flavanols - This group can be further broken down into three classes: catechins, theaflavins, and proanthocyanidins. Catechins and theaflavins are found in teas. Green tea is higher in catechin, while black teas are richer in theaflavins. One compound in particular, epicatechin, has been shown to improve blood flow and may be good for cardiac health. Cocoa, the main ingredient of dark chocolate, contains high amounts of epicatechin. Proanthocyanidins are found in chocolate, apples, berries, red grapes and red wine. These nutrients can increase the vitamin c inside cells and may inhibit the destruction of collagen, the most abundant protein in the body.
• Flavanones - This group is found in citrus fruits and juices, such as oranges, grapefruits and lemons
• Flavonols - The most abundant and commonly known flavonoid in this group is quercetin, found in yellow onions, scallions, kale, broccoli, apples, berries and teas. Red wine is also high in quercetin.
• Flavones - Dietary intake of this group is relatively low, as flavones are primarily found in the skin of citrus fruits. This group also contains foods such as parsley, thyme, celery and hot peppers.
• Isoflavones - This group is the most bioavailable of all flavonoids, and contains the soy flavonoid genistein. Legumes also contain isoflavones. Some studies have found that soy flavonoids can reduce blood cholesterol, prevent osteoporosis, and may ease menopausal symptoms.

Nonflavonoids

Non-flavonoid antioxidants can be broken down into three categories: vitamins, minerals and plant pigments.

• Vitamins C and E are the primary vitamin antioxidants. Vitamin C is found in citrus fruits such as oranges and lime, and in green vegetables like broccoli and greens. Vitamin E is usually found in foods with healthy fats, such as nuts and seeds and oils such as safflower and corn oil. It is also in whole grains.
• Selenium is a mineral that is a component of antioxidant enzymes. It is found in meat, fish, eggs and grains.
• There are three main types of plant pigments with antioxidant activity. Carotenoids are the orange pigments found in foods such as pumpkin, carrot and sweet potato. Beta-carotene is a precursor to Vitamin A. Lutein is found in dark green vegetables such as kale, broccoli, kiwi, Brussels sprouts and spinach. Lutein is best known for being a nutrient that benefits the eyes. Lycopene is the red pigment found in tomatoes, pink grapefruit and watermelon.

Much research has been done on the health benefits of antioxidants, but most experts agree that the nutrients should be consumed as food, and not from dietary supplements.