World Food Prize Winners: Why Sweet Potato Color Matters


By Tracie McMillan

“The Plate,” National Geographic • June 28, 2016

A handful of scientists have spent the last 15 years convincing Africans to swap white sweet potatoes for their more colorful and vitamin-packed cousins, orange sweet potatoes. But if a tuber associated with holiday excess in the U.S. sounds like a strange focus for science, consider this: Those scientists are receiving the world’s most prestigious prize for agricultural research, the $250,000 World Food Prize, which celebrates agricultural efforts that combat food insecurity.

This year’s award not only recognizes the “biofortification” of starchy white- and yellow-fleshed potatoes with Vitamin A by two African scientists—Maria Andrade of Mozambique and Robert Mwanga of Uganda— but the success of a sophisticated campaign, overseen by American scientist Jan Low, to make the food both accessible and desired. All threes scientists work for the International Potato Center.(The WFP also included a fourth scientist, Howarth Bouis, for his general work developing biofortification practices.)

So why sweet potatoes, and how do you convince a whole continent to change its eating habits? It’s not easy.

When sweet potatoes were first introduced to the African continent in the 1600s, starchy white and yellow varieties took hold in local food cultures, and became commonplace alongside other tubers like cassava. But pale sweet potatoes are significantly lower in vitamins than the damper, bright orange potatoes familiar to Americans, says Low. At the same time, all varieties of sweet potato were generally considered “a crop of the poor,” says Low; some people avoided it as such.

Meanwhile, child malnutrition is a serious problem in the developing world and deficiency in Vitamin A is the leading cause of child blindness. In much of sub-Saharan Africa, more than one-fifth of preschool-age children have a Vitamin A deficiency, and in some countries it nears 50 percent. (In the U.S., by comparison, it is less than 2 percent.)

To combat that problem, researchers began experimenting with high-nutrient foods that were easy to grow—like sweet potatoes. Throughout the 1990s, says Mwanga, researchers studied the use of orange sweet potatoes to improve community nutrition in the Philippines, Mozambique and Uganda. When those studies showed that sweet potatoes could indeed increase the consumption of Vitamin A and beta carotene, and accordingly strengthen immune systems and lower the incidence of blindness, says Mwanga, they faced the next question: What variety of sweet potatoes should they promote?

Few African farmers or consumers were interested in the mushier flesh of American-style orange sweet potatoes. So researchers bred starchy ones that contained more beta carotene—and took on an orange color as a result. That solved the variety question.

But researchers couldn’t get seed companies on board, because sweet potatoes aren’t grown from seed; they’re grown from vine cuttings. So researchers partnered with groups of farmers, helping them launch tiny businesses of growing and selling sweet potato cuttings for other subsistence farmers to grow at home. If the plants are well cared for, says Low, families can get two or three crops each year from the same plants.

The final piece of promoting the potatoes, says Low, was creating public nutrition education campaigns. Rather than market sweet potatoes alone, she says, researchers promoted the idea that foods rich in Vitamin A and beta carotene are orange—like the sweet potato. Advocates drove orange trucks around emblazoned with images of sweet potatoes and community groups staged nutrition-themed theater productions. Whole buildings were painted orange to promote the idea that orange food offers life-saving nutrients, said Low.

By most accounts, it has worked well: Today, near two million households across ten African countries are planting or buying these fortified sweet potatoes, according to the World Food Prize. Researchers are also beginning to work with processors to sell vacuum-packed sweet potato purée in urban markets, where people may no longer be growing their own food.

Still, some observers question whether biofortification is enough. Much of the malnourishment in the developing world, observes Raj Patel—a leading critic of industrial agriculture who was recently named a James Beard Foundation Leadership Awardee—is the result of economic inequality stemming from specific development policies. “[Sweet potatoes] don’t really get us any further in addressing the core issue of why people can’t access or afford to eat healthy food,” says Patel. “Think of them as a signature food for an era of poverty with added vitamins.”

Low emphasizes that her focus on sweet potatoes was specific to her vocation as a researcher: “We’re working with caregivers to empower them with knowledge to make good nutritional choices,” she says. “That doesn’t mean others shouldn’t be advocating for greater change on the policy side.”

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