PNAS

No breakdown.
Normal wheat (top) contains starch that is easier to digest than that in modified wheat.

Take THAT, Dr. Atkins

Staff Writer

Pasta, bread, crackers: Supermarket shelves are lined with products made from wheat. And that's not necessarily a good thing. When wheat is highly processed, the body converts its starches into sugar, potentially contributing to obesity and diabetes. Now a team of researchers has engineered a new variety of the grain that avoids those drawbacks by holding onto its starch as fiber.

Starch consists of a mix of two kinds of molecules: amylopectin and amylose. Amylopectin is a branched molecule that remains fairly soluble in the digestive tract, allowing enzymes to break it down quickly into sugar. The long chains of glucose that make up amylose, in contrast, form clumps that resist digestion. Plant breeders have successfully created corn with less amylopectin and more amylose, which has been marketed as health foods because the body is less able to turn it into sugar.

The starch level of wheat has been tougher to manipulate. But recently, a team led by Matthew Morell of CSIRO Plant Industry in Canberra, Australia, has discovered which genes impact starch formation in an experimental variety of wheat. When they damped down the expression of two of these genes, called SBEIIa and SBEIIb, the relative amount of indigestible amylose in the starch rose to almost 75%, compared to 25% in typical grain. "We were pretty excited," says Morell.

The team then milled the grain, made pellets, and fed them to six rats for 13 days. Compared to six rats that ate standard wheat, these rats had signs of healthier bowels, such as more than twice as much short chain fatty acids--one kind of which may lower the risk of colorectal cancer. Next, the group plans to conduct feeding trials in pigs. They hope to use the findings, reported online today in Proceedings of the National Academies of Sciences, to help traditional wheat breeders achieve the same results without the controversy of genetic engineering (ScienceNOW, 20 January 2004).

The popularity of this new wheat will depend on the quality of the flour, says Alan McHughen of the University of California, Riverside, who has worked on wheat. "Any genetic change to the wheat starch will impose a change to the flour characteristics. And this will raise a red flag to the millers and bakers, a notoriously conservative group who view any change to their 'perfect' food with great suspicion." Morell says his team has concocted a few breads and bakery products, and the flour "is pretty good to work with."

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