A feeding study finds that wheat bred for high zinc content raises the intake of this vital micronutrient, promising to improve nutrition security for the staple-dependent poor.

Wheat was prominent in the Green Revolution, which improved food security for millions of people. Today, wheat is central to enhancing nutrition security for millions more who rely on it for their daily bread. Through a new strategy called biofortification, scientists are breeding higher amounts of critical micronutrients into staple food crops. One nutrient being bred into wheat is essential for survival - zinc.

Zinc deficiency kills more than 400,000 children every year and stunts millions more. Most poor people who subsist on a staple food such as wheat and little else suffer from zinc deficiency. While a diverse diet that includes foods such as leafy vegetables and fruits, is ideal, poor people who live in rural areas may not be able to grow these foods or afford them even if they are available in local markets. But, by growing biofortified staple crops, they will be able to meet some of their micronutrient requirement with foods they already eat daily.

However, there is a catch. Wheat, like many cereals, contains phytate, a phosphorus compound that inhibits the digestive system's absorption of minerals such as zinc. Phytate may contribute to the high rates of zinc deficiency found in South Asian communities that rely upon unrefined wheat products for sustenance. But phytate also plays an important role in seed viability, plant growth and crop yield. Therefore, instead of reducing phytate content in the edible portions of staple food crops to enhance human nutrition, scientists are breeding in more zinc to compensate for their inhibitory effect.

Last year, sufficient quantities of conventionally bred high-zinc wheat were available from the International Maize and Wheat Improvement Center to investigate for the first time whether more zinc can actually be absorbed from biofortified wheat than from ordinary wheat and the extent to which phytate inhibits zinc uptake. A team of researchers with the HarvestPlus Challenge Program fed, as part of a controlled feeding trial, a group of Mexican women, whose usual diet is high in grain and phytate content, tortillas made from zinc-biofortified wheat flour. They found substantially higher intake of bioavailable zinc from the zinc‐biofortified wheat.

And what of the phytate? Milling wheat to produce flour wears down and removes bran and germ, which reduces the phytate content. The amount of the reduction depends on the extraction, the degree to which the bran and germ are removed. For example, whole-wheat flour has 100% extraction. Unfortunately, milling also reduces zinc content. Scientists found that 80% extracted biofortified wheat flour still had 65% more zinc than equally extracted control wheat flour, while the phytate content in the two flours was similar. Despite the inhibitory effect of the phytate, the higher zinc content of the biofortified wheat resulted in 33% higher zinc absorption than observed with the control wheat. So, despite the significant loss of zinc at 80% extraction, the reduction in phytate and the higher amounts of zinc from biofortification meant greater zinc absorption. p

The research team ascertained from this study that just 300 grams of wheat flour could provide two-thirds of the physiological zinc requirements of adult women. The study justifies longer‐term feeding trials in target regions where farmers will grow zinc‐biofortified wheat to account for environmental conditions that may affect the zinc content of wheat. It also validates models that predict the inhibitory affect of phytate on zinc absorption, which HarvestPlus will use to refine breeding targets for zinc in wheat.

"We also need to determine the appropriateness of existing models for determining zinc absorption at different levels of phytate intake for children, because most studies so far have focused on adults," says Erick Boy, head of nutrition in HarvestPlus. "Children, as you know, are most vulnerable to micronutrient malnutrition."

HarvestPlus plans similar studies with its partners in 2010-2011 for pearl millet in India and maize in Zambia. Plant breeders and nutritionists will need to work closely together to ensure that crops with sufficient amounts of micronutrients to provide nutritional benefit can be bred and grown. By integrating biofortification into plant breeding programs, staple food crops are once again poised to become part of the solution to food and nutrition insecurity.

For the full study results, see Jorge L. Rosado, K. Michael Hambidge, Leland V. Miller, Olga P. Garcia, Jamie Westcott, Karla Gonzalez, Jennifer Conde, Christine Hotz, Wolfgang Pfeiffer, Ivan Ortiz-Monasterio and Nancy F. Krebs. 2009. The quantity of zinc absorbed from wheat in adult women is enhanced by biofortification. Journal of Nutrition Oct 139 (10):1920-5.