antioxidants.

With the increase in product labels claiming to contain antioxidants, have a high ORAC score, fight aging, and prevent cancer -- I thought it was definitely time to clarify what exactly an antioxidant is and does.
Antioxidants are defined as any substance that prevents damage that is caused by oxygen (such as free radicals).  This oxidative damage can occur when a molecule becomes unstable after a bond is broken and electrons become unpaired forming free radicals.  Once free radicals are formed, they remain very reactive as they search for an electron to steal from other molecules.   As they continue to react with other molecules, such as DNA and cellular membranes, free radicals cause cellular damage which can contribute to the development of certain conditions and diseases (cardiovascular disease, cancer, cognitive impairment).  This free radical process can occur from natural cellular factors and/or from environmental activities (i.e. smoking, pollution, sun-bathing). 
Antioxidants are helpful by providing a calming effect on free radicals by donating an electron to these overactive molecules.  With the electron donation from antioxidants, free radicals will not cause oxidative damage to other cellular molecules, making them vitally important.   Antioxidant compounds consist of vitamins, minerals, polyphenols, and carotenoids. 
So now that the biology is out of the way, where are these compounds naturally found?  Below is a list of the antioxidant compounds and some natural food sources.

Vitamins
Vitamin A: Dairy products and fish
Vitamin C: Berries, citrus fruits, and bell peppers
Vitamin E: Seeds and nuts

Minerals
Selenium: Tuna, meat, nuts, and seeds

Polyphenols
Resveratrol: Grapes and red wine
Flavonoids: Green tea, cocoa, berries, broccoli, apples, pears, flaxseed, red beans, and lentils
Phenolic Acids: Whole grains and coffee

Carotenoids
Beta-Carotene: Pumpkin, carrots, and cantaloupe
Lutein: Leafy green vegetables
Lycopene: Tomato and watermelon

Antioxidants in food are measured through a test tube analysis called Oxygen Radical Absorbance Capacity (ORAC) score.  A higher ORAC score = higher antioxidant activity = higher protection from free radical damage.  Some of the highest antioxidant foods are plant foods.  So the moral of the story: have a ton variety in your diet that includes plenty of fruits, vegetables, legumes, nuts, and whole grains to help prevent the numerous health conditions that result from oxidative stress!