By Becky C. Williamson and Deepa Handu, PhD, RD, LDN

Antioxidants are a hot topic of interest as researchers continue to demonstrate the disease fighting potential within these substances. Because kidney patients need to analyze their diets in many different aspects, it’s important to determine whether or not including antioxidants in the diet is beneficial, or even feasible.

What are antioxidants anyway?
First of all, let’s take a closer look at what antioxidants are. As the word implies, “antioxidant” translates to “against oxidation.” Oxidation is a normal chemical process that occurs in our body when molecules are broken down along with oxygen to produce energy, such as converting the food we eat into fuel for our bodies to burn. Excessive oxidation of some nutrients, such as fat and cholesterol can release unstable molecules, called “free-radicals.” Disproportionate levels of free-radicals can cause a cascade of damage to otherwise healthy cells leading to a myriad of chronic conditions, such as cardiovascular disease, nerve degeneration, cancer and impaired DNA. Antioxidants serve to stabilize free-radicals, by maintaining a healthy oxidant-antioxidant balance, protecting the body from such ailments.

Where are antioxidants found?
Some antioxidants are made in the body, but many are available in the abundance of fruits and vegetables we eat every day. The brilliant colors and delicate flavors of fruits and vegetables are produced by plant chemicals, or “phytochemicals,” which have been shown to contain potent antioxidant properties. Purple, blue, and deep red-colored fruits and vegetables contain the phytochemical “flavinoids” which accounts for the rich color. Flavanoids help protect against cellular oxidation and reduce the risk of heart disease. Green, yellow, orange and red fruits and vegetables are chock full of vitamin A and C, among other phytochemicals, which also help bolster antioxidant defenses. Oils extracted from some plants, such as olive and canola, contain vitamin E, a fat soluble vitamin and healthful antioxidant. Incidentally, the combination of vitamin C and E has been shown to increase their free-radical fighting potential.

All this is great news for kidney patients because most fruits and vegetables tend to be high in fiber, low in phosphorus and sodium. Potassium levels can vary, but there are no forbidden fruits or vegetables. Talk to your registered dietitian to determine the appropriate daily amount of potassium to aim for, and which fruit and vegetable combinations work best for your stage of CKD. A combination of bright colors and flavors found in fruits and vegetables can make a kidney-friendly meal appetizing and healthful.

Here’s an easy color-coded table with some fruits and vegetables containing specific antioxidants. 

Color	Food Sources	Potential Benefit
Purple	Purple & Red Grapes; Eggplant	Flavonoids - protect against oxidation, hear disease; reduces inflammation
Blue	Blueberries	Anthocyanidins, a form of flavonoid - boost cellular antioxidant defense & may help maintain normal brain function. High vitamin C
Green	Green Peppers, Cabbage	Green Peppers - High vitamin C; Cabbage - "Sulforaphane" which may prevent some cancers, High vitamin C
Yellow	Onions, Garlic, Summer Squash, Olive Oil	Onions & garlic contain sulfur compounds, to help flavor food; Onions - "Quercetin" aids in detoxification of undesirable compounds & reduces heart disease; Garlic reduces inflammation, prevents plaque formation on teeth, lowers cholesterol; Summer squash - High vitamin A; Olive oil - Vitamin E; can help with immune function and DNA repair
Orange	Carrots	Beta-carotene; High vitamin A
Red	Apple, Raspberries, Cherries, Strawberries, Cranberries, Red Peppers	Apples - Quercetin; reduces inflammation; Raspberries, strawberries, cherries and cranberries - Anthocyanidins & high vitamin C; Cranberries - protects both digestive & urinary tract, defends against some cancers; Red peppers - "lycopene", protect against some cancers, High in vitamin A & C

Becky C. Williamson holds a bachelor’s degree in Nutrition and Food Science from San Jose State University in California (1992). She is currently a M.S. Nutrition and Wellness candidate at Benedictine University in Chicago. Although Becky’s concentration is in sports nutrition, she has a special interest in renal dietetics.

Deepa Handu, PhD, RD, holds a doctorate degree in Human Nutrition (Michigan State University, 2005) and a master degree in Food Science and Human Nutrition from India. Before joining Benedictine University, Dr. Handu taught nutrition and research courses at Loyola University Chicago.

This article originally appeared in the September 2009 issue of Kidney Beginnings: The Magazine.

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