Antioxidants have the ability to neutralize and reduce free radical damage. To deeply comprehend the power of antioxidants, you must first understand what free radicals are and how they react in the body. Free radicals are harmful compounds that have an unpaired electron, an aspect of their structure that makes them highly unstable. Their instability causes them to wreak havoc on cells, fatty acids, and other structures in your body. Free radicals also act as catalysts for diseases, many diseases.
Normal metabolic processes in our bodies promote oxidation, a stage of metabolism where free radicals are produced. Eating, breathing, physical activity all play a part in the oxidation process and the formation of free radicals. Cell, organ, bone, joints, and immune system damage results from excessive free radicals. The damage is over the long haul. In fact, free radicals and oxidation are actually what cause the visible signs of aging and contribute to the aging process.
The Best Dietary Antioxidants
Antioxidants are available in many forms and are present in virtually all foods, whether they are of plant or animal origin. Generally, natural plant foods are the best source of antioxidants and also offer many other nutritional benefits. Although antioxidants in supplement form are beneficial, food-based antioxidants are thought to be better absorbed.
Here are 9 of the best dietary antioxidants readily available in natural, whole foods:
Plant pigments are the main source of anthocyanidins. The anthocyanidins in blueberries, for example, may be protective against DNA damage from UV radiation.  One study on the anthocyanidins in the Hibiscus flower suggested antidepressant effects from its naturally-occurring pigments.  Anthocyanidins have also been shown to offer certain benefits against lung and colorectal cancer, cognitive decline, and even gluten intolerance.    
Food sources include: oranges, cherries, berries, eggplant, radishes, red grapes, and even red wine.
2. Beta Carotene
Beta carotene is in many fruits, grains, oils, and vegetables. A member of the carotenoids family, it’s recognized by its orange-red color. It is a precursor to vitamin A, a fat-soluble vitamin that requires the presence of dietary fat for proper absorption. Beta carotene's antioxidant effects are plentiful, with eyesight being its most popular benefit. Data from the Age-Related Disease Study suggests that beta carotene is a key nutrient for preventing age-related macular degeneration. 
Food sources of beta carotene include: carrots, broccoli, spinach, kale, cantaloupe, mangoes, apricots, goji berries, squash, pumpkin greens, and sweet potatoes.
3. Caffeic and Ferulic Acid
Ferulic acid is derived from the biosynthesis of caffeic acid, and both have mighty antioxidant effects. Isolated caffeic acid has been shown to play a role in fighting inflammatory diseases.  Ferulic acid, on the other hand, may be a potential therapy for mood disorders, according to some research. 
Foods containing caffeic and ferulic acids include: apples, pears, oranges, pineapple, artichoke, coffee, peanuts, oregano, turmeric, steel-cut oats, rice, kale, basil, thyme, and rosemary.
Flavonols are found in a range of fruits, vegetables, tea, spices, and herbs. The well-known antioxidants quercetin and kaempferol are a type of flavonols. These flavonol antioxidants show potential for fighting inflammatory conditions. 
Kaempferol, specifically, has been shown to be beneficial for blood sugar and skin health. Studies have also shown that kaempferol positively affects metabolism and thyroid hormone production.  Along with quercetin, kaempferol has also been shown to promote a calm mood. Interestingly enough, these effects occur only when the flavonols are broken down during digestion by intestinal microflora.  That being said, it may be important to maintain a healthy, probiotic-supported digestive tract to see the benefits from these antioxidants!
Foods high in flavonols include: apples, apricots, raspberries, cocoa, chocolate, blackberries, onions, red wine, and green and black teas.
Also in the flavonoid family are flavanones, compounds with potent anti-inflammatory activity. Humans and animal studies indicate neuroprotective effects from this antioxidant. Researchers have discovered that flavanones support the digestion and absorption of carotenoids found in foods like carrots and bell pepper, further improving the nutrient's effect in the body. 
Foods containing flavanones include: oranges, lemons, limes, grapefruit, and milk thistle.
Similar to beta carotene, lutein belongs to the carotenoid plant pigments responsible for promoting retina health. Lutein occurs naturally in green vegetables, fruits, and even some animal products. Lutein may potentially lower your risk for developing cataracts and age-related macular degeneration. 
Foods containing lutein include: spinach, kale, collard greens, broccoli, parsley, green peas, carrots, celery, squash, okra, egg yolks, and pumpkin.
Another member of the carotenoid family, lycopene typically makes up the red pigment in vegetables and fruits. Its best source in the human diet comes from tomatoes, although it can also be found in red bell peppers and various red-colored fruits and vegetables. A highly-potent antioxidant, lycopene may be helpful in the fight against cancer.  Lycopene has also been shown to increase HDL cholesterol levels ("good" cholesterol), possibly reducing the risk for heart disease. 
Foods containing lycopene include: spinach, pumpkin, squash, papaya, watermelon, red bell peppers, red (pink) grapefruit, and sweet potatoes.
It is widely believed that proanthocyanidin, a type of flavanols, may support the blood vessels. It also offers benefits to the cardiovascular system. High amounts of this antioxidant are found in cacao (chocolate) – it's responsible for the food’s health benefits.  Some studies indicate that proanthocyanidins are ten times more powerful than vitamin C and may even act as an internal sunscreen that protects the skin against UV radiation! 
Foods containing proanthocyanidins include: apples, red grapes and red wine, cranberries, strawberries, cinnamon, peanuts, chokeberry, and black and green tea.
Sulforaphane is a sulfur-based antioxidant found in cruciferous vegetables. Some findings suggest it discourages breast cancer tumors.  Another study reported positive effects against colon cancer. Other studies have linked it to normal blood pressure, heart health, and cholesterol. It also appears to activate mechanisms which maintain balanced blood glucose levels. 
Foods containing sulforaphane include: broccoli, cabbage, cauliflower, kale, turnip, brussel sprouts, radish, collard greens, and watercress.
One Final Thought
When it comes to protecting your health, you can never go wrong with incorporating more antioxidants into your diet. Do remember that although antioxidants are good nutrition, they're not pharmaceutical medicine and shouldn't be thought of as such. Vegetables, fruits, nuts, and seeds are an extraordinary source of dietary antioxidants, so a diet comprised of at least half to three quarters of these foods should be a great source of antioxidants.
- Liu W, Lu X, He G, Gao X, Li M, Wu J, Li Z, Wu J, Wang J, Luo C. "Cytosolic protection against ultraviolet induced DNA damage by blueberry anthocyanins and anthocyanidins in hepatocarcinoma HepG2 cells." Biotechnol Lett. 2013 Apr;35(4):491-8. doi: 10.1007/s10529-012-1105-2.
- Shewale PB, Patil RA, Hiray YA. Antidepressant-like activity of anthocyanidins from Hibiscus rosa-sinensis flowers in tail suspension test and forced swim test." Indian J Pharmacol. 2012 Jul-Aug;44(4):454-7. doi: 10.4103/0253-7613.99303.
- Kausar H, Jeyabalan J, Aqil F, Chabba D, Sidana J, Singh IP, Gupta RC. "Berry anthocyanidins synergistically suppress growth and invasive potential of human non-small-cell lung cancer cells." Cancer Letter. 2012 December 1;325(1):54-62. doi: 10.1016/j.canlet.2012.05.029.
- Devore EE, Kang JH, Breteler MM, Grodstein F. "Dietary intakes of berries and flavonoids in relation to cognitive decline." Ann Neurol. 2012 Jul;72(1):135-43. doi: 10.1002/ana.23594.
- Kausar H, Jeyabalan J, Aqil F, Chabba D, Sidana J, Singh IP, Gupta RC. "Berry anthocyanidins synergistically suppress growth and invasive potential of human non-small-cell lung cancer cells." Cancer Lett. 2012 Dec 1;325(1):54-62. doi: 10.1016/j.canlet.2012.05.029. Epub 2012 May 29.
- Tozzi S, Zanna N, Taddei P. "Study on the interaction between gliadins and a coumarin as molecular model system of the gliadins-anthocyanidins complexes. Food Chem. 2013 Dec 15;141(4):3586-97. doi: 10.1016/j.foodchem.2013.05.136.
- Cheung LK, Eaton A. "Age-related macular degeneration." Pharmacotherapy. 2013 Aug;33(8):838-55. doi: 10.1002/phar.1264.
- Figueiredo-Rinhel AS, Kabeya LM, Bueno PC, Jorge-Tiossi RF, Azzolini AE, Bastos JK, Lucisano-Valim YM. "Inhibition of the human neutrophil oxidative metabolism by Baccharis dracunculifolia DC (Asteraceae) is influenced by seasonality and the ratio of caffeic acid to other phenolic compounds." J Ethnopharmacol. 2013 Sep 25. pii: S0378-8741(13)00654-5. doi: 10.1016/j.jep.2013.09.019.
- Pathak L, Agrawal Y, Dhir A. "Natural polyphenols in the management of major depression." Expert Opin Investig Drugs. 2013 Jul;22(7):863-80. doi: 10.1517/13543784.2013.794783.
- Wang L, Tu YC, Lian TW, Hung JT, Yen JH, Wu MJ. "Distinctive antioxidant and antiinflammatory effects of flavonols. Agric Food Chem. 2006 Dec 27;54(26):9798-804.
- da-Silva WS, Harney JW, Kim BW, Li J, Bianco SD, Crescenzi A, Christoffolete MA, Huang SA, Bianco AC. "The small polyphenolic molecule kaempferol increases cellular energy expenditure and thyroid hormone activation." Diabetes. 2007 Mar;56(3):767-76.
- Vissiennon C, Nieber K, Kelber O, Butterweck V. "Route of administration determines the anxiolytic activity of the flavonols kaempferol, quercetin and myricetin--are they prodrugs?." J Nutr Biochem. 2012 Jul;23(7):733-40. doi: 10.1016/j.jnutbio.2011.03.017.
- Claudie DM, Alexandrine D, Bertrand C, Franck T, Marie-Josephe A. "Citrus flavanones enhance carotenoid uptake by intestinal Caco-2 cells." Food Funct. 2013 Oct 24;4(11):1625-31. doi: 10.1039/c3fo60212e.
- Murthy RK, Ravi K, Balaiya S, Brar VS, Chalam KV. "Lutein protects retinal pigment epithelium from cytotoxic oxidative stress." Cutan Ocul Toxicol. 2013 Jul 18.
- Soares ND, Teodoro AJ, Oliveira FL, Santos CA, Takiya CM, Junior OS, Bianco M, Junior AP, Nasciutti LE, Ferreira LB, Gimba ER, Borojevic R. "Influence of Lycopene on Cell Viability, Cell Cycle, and Apoptosis of Human Prostate Cancer and Benign Hyperplastic Cells.." Nutr Cancer. 2013 Sep 20.
- Cuevas-Ramos D, Almeda-Valdés P, Chávez-Manzanera E, Meza-Arana CE, Brito-Córdova G, Mehta R, Pérez-Méndez O, Gómez-Pérez FJ. "Effect of tomato consumption on high-density lipoprotein cholesterol level: a randomized, single-blinded, controlled clinical trial. Diabetes Metab Syndr Obes. 2013 Jul 26;6:263-73. doi: 10.2147/DMSO.S48858.
- Arranz S, Valderas-Martinez P, Chiva-Blanch G, Casas R, Urpi-Sarda M, Lamuela-Raventos RM, Estruch R. "Cardioprotective effects of cocoa: clinical evidence from randomized clinical intervention trials in humans." Mol Nutr Food Res. 2013 Jun;57(6):936-47. doi: 10.1002/mnfr.201200595.
- Vaid M, Prasad R, Singh T, Jones V, Katiyar SK. "Grape seed proanthocyanidins reactivate silenced tumor suppressor genes in human skin cancer cells by targeting epigenetic regulators." Toxicol Appl Pharmacol. 2012 Aug 15;263(1):122-30. doi: 10.1016/j.taap.2012.06.013.
- Li Q, Xia J, Yao Y, Gong DW, Shi H, Zhou Q. "Sulforaphane inhibits mammary adipogenesis by targeting adipose mesenchymal stem cells." Breast Cancer Research and Treatment. 2013 September;141(2):317-24. doi: 10.1007/s10549-013-2672-1.
- Bahadoran Z, Mirmiran P, Azizi F. "Potential efficacy of broccoli sprouts as a unique supplement for management of type 2 diabetes and its complications." J Med Food. 2013 May;16(5):375-82. doi: 10.1089/jmf.2012.2559.
†Results may vary. Information and statements made are for education purposes and are not intended to replace the advice of your doctor. If you have a severe medical condition or health concern, see your physician.