A free radical is an atom or molecule that has a single unpaired electron in an outer shell. While few free radicals are chemically reactive such as melanin, most biologically-relevant free radicals are highly reactive. For most biological structures, free radical damage is associated with oxidative damage. Antioxidants are reducing agents, and limit the damage to biological structures by passivating free radicals. Just as iron rusts from oxidative processes, your body can rust with age due to free radicals and the oxidation process.

In the 1950s, Denham Harman first proposed the free radical theory on aging, and extended the idea to implicate mitochondrial production of reactive oxygen species in the 1970s.

When the body uses oxygen, by-products cause oxidative damage to cells within the body. Free radicals come from smoking, pollution, poisons, fried foods, chemicals, and even from normal metabolism. The damage caused by free radicals is associated with an increased risk of many chronic diseases. Antioxidant vitamins and minerals help to reduce the damage that free radicals cause.

One of the most critical substances in foods, are antioxidants. One important way to look at the health value of a food is to find its antioxidant level. These substances are found in plants which play a vital role in protecting the plant. Due to the level of sunlight that plants get, antioxidants help to limit the damage to cells. In the human body they can help to reduce skin damage, which could lead to skin cancer. When eating vegatables with high antioxidant levels our bodies use them to repair cell damage within our own human body. Antioxidants are nature's own anti-aging medicine. In various studies they have been shown to help prevent cancer, heart disease, and countless other illnesses.

Below is a list of various foods commonly eaten that carry high yields of antioxidants. This is a limited list and many of the best are green leafy vegetables, also known as cruciferous vegetables.

_Sources:

Xianli Wu, Gary R. Beecher, Joanne M. Holden, David B. Haytowitz, Susan E. Gebhardt, and Ronald L. Prior. "Lipophilic and Hydrophilic Capacities of Common Foods in the United States." J. Agric. Food Chem., 52 (12), 4026-4037, 2004.

Antiodixant Levels of Common Foods

FOOD PORTION ANTIOXIDANT LEVEL

dried red beans 1/2 cup 13727 

wild blueberries 1 cup 13427

dried red kidney bean 1/2 cup 13259

pinto beans 1/2 cup 11864

blueberries 1 cup 9019

whole cranberries 1 cup 8983

cooked artichoke hearts 1 cup 7904

blackberries 1 cup 7701

prunes 1/2 cup 7291

raspberries 1 cup 6085

strawberries 1 cup 5938

red delicious apples 1 apple 5900

granny smith apples 1 apple 5381

pecans 1 ounce 5095

sweet cherries 1 cup 4873

black plum 1 4844

cooked Russet potato 1 4649

dried black beans 1/2 cup 4181

plum 1 4118

gala apple 1 3903

Some free radicals play an important role in a number of processes within biology, some that are necessary for life, such as the ones that perform intracellular killing of bacteria by phagocytic cells like granulocytes and macrophages. There is also redox signaling, a process in which free radicals have been implicated in certain cell signalling processes.

Superoxide and hydroxyl radical are the two most important oxygen-centered radicals. Seeing as they are derived from molecular oxygen under reduction they are highly reactive. The reactivity allows them to participate in unwanted side reactions which lead to cell damage. Cancer in its many forms is thought to be the result of free radical reactions between itself and DNA. These reactions cause mutations that affect the cell cycle and potentially lead to malignancy. Atherosclerosis and other symptoms of aging are also linked to the oxidation caused by free radical reactions in the chemicals of the human body. Alcohol induced liver damage, and emphysema are both thought to be caused more from free radical damage than from the smoke and alcohol themselves, due to the reactions the body induces when taking in these foreign substances.

 Vitamin A and Carotenoids

    Carrots, squash, broccoli, sweet potatoes, tomatoes, kale, collards, cantaloupe, peaches, and bright-colored fruits and vegatables.

Vitamin C

     Citrus fruits like oranges and limes, green peppers, broccoli, green leafy vegetable, strawberries and tomatoes.

Vitamin E

      Nuts and seeds, whole grains, green leafy vegetables, vegetable oil, and liver oil.

Selenium

      Fish & shellfish, red meat, grains, eggs, chicken and garlic  (red meat and seafood should be limited due to other harmful traits.)

Some common phytochemicals

• Flavonoids / polyphenols
  • soy
  • red wine
  • purple grapes or Concord grapes
  • pomegranate
  • cranberries
  • tea
• Lycopene
  • Tomato and tomato products
  • pink grapefruit
  • watermelon
• Lutein
  • dark green vegetables such as kale, broccoli, kiwi, brussels sprout and spinach
• Lignan
  • flax seed
  • oatmeal
  • barley
  • rye

Vitamin-like Antioxidants:

• Coenzyme Q10 (CoQ10)
• Glutathione

Antioxidant enzymes made by the body:

• superoxide dismutase (SOD)
• catalase
• glutathione peroxidase