Food "Farmacy": The Case for Carrots
by Erica Renaud

No press release marks the exact date of the birth of agriculture, but for about 10,000 years farmers have enjoyed a unique position of power in human society. By selecting for certain desirable crop traits, they have literally shaped the food we eat: the size of our tomatoes, the number of peas in a pod, the number of rows on an ear of corn, and the size of the kernels, and even the color of carrots, are all characteristics for which we can thank both ancient and modern farmers/breeders.

This selection process has not always been, nor is it now, completely seamless: it is frequently a baffling game of give-and-take with a plant and its "deck of cards," referring to the genome or germplasm of a particular crop. It is common, for example, that selecting for one resource-demanding trait (high yields) is achieved only at the expense of another equally desirable trait (disease resistance, stalk strength, vitamin content, etc.). It is as if the plant is saying, "Look, you can't have it all." But we do want it all—flavor and nutrition, not to mention vigorous growth and high yields. As research into the health benefits of various plant compounds advances, scientists have identified cues that are indicators of that most elusive of traits, a fully loaded nutritional package. One of those cues is color.

Filling your garden and plate with a variety of colors is not just visually pleasing, but vitally and vibrantly health inducing. Studies examining the health benefits of fruits and vegetables are revealing the disease-preventive powers of the phytochemicals (bioactive chemical compounds that occur naturally in plants) that give plants their distinctive colors. Foods that are deep-blue, purple, red, green, or orange contain high levels of these phytochemicals (in this case, certain pigments), which can protect the body from numerous diseases, as well as enhance immunity and overall health.

Take carrots, a vegetable common to all of our plates and palates and an excellent case study for the topic at hand. The average American consumes 5 lbs. of carrots a year, according to the USDA's Economic Research Service. Carrots are our primary source of vitamin A, with a single full-size carrot more than fulfilling an adult's daily quotient. Two decades ago, the University of Wisconsin streamlined their carrot breeding program to focus on an orange carrot packed with beta-carotene, the orange pigment used by the body to create vitamin A. The result is a carrot with 75% more beta-carotene than the historical carrot.

In more recent years, however, US breeders Phil Simon (U. of Wisconsin), John Navazio (Evergreen State College), and Leonard Pike (Texas A&M), have been rediscovering the merits of colors other than orange. Going back to historical germ plasm (carrots originated in Afghanistan and were historically white or purple), these breeders have challenged the "orange only" convention of carrot breeding and set the stage for a colored-carrot comeback by focusing on pigments such as lycopene, anthocyanin, xanthophyll, and lutein. Together with beta-carotene, these pigments are all categorized as carotenoids.

Different strains of carrots contain varying types and amounts of these pigments; Dr. Phil Simon is working to map all the genes that play a part in synthesizing carotenoids in major carrot lines. Simon now knows of twenty genes that are involved. However, determining a particular gene's role in generating carotenoids is not that straightforward because the plant's expression of a given gene can change in different stages of its life cycle.

The Color Map: What do we know about the nutritional value of colored carrots?

• Xanthophylls, similar to beta-carotene, give yellow carrots their golden colors; they are linked to eye health and may reduce the incidence of lung and other cancers.
• Lycopene, found in red carrots, is a type of carotene also found in tomatoes. It is believed to help prevent heart disease and, in conjunction with other phytochemicals, reduce the risk of certain cancers, including prostate cancer.
• Anthocyanins and pigments of the flavonoid (as opposed to carotenoid) class are found in purple carrots. In the human body these pigments act as powerful antioxidants, immobilizing harmful free radicals. Anthocyanins can also help reduce the risk of heart disease by slowing blood clotting.
• White carrots lack pigment but may contain other beneficial phytochemicals. More research is needed.
• Lutein is one of the hydroxy carotenoids found in yellow and orange carrots and makes up the macular pigment of human retinas. Consuming foods high in lutein may increase the density of this pigment and decrease the risk for developing macular degeneration and other age-related diseases.