May I Propose a High-Fiber Toast?

It’s not just about being “regular,” as those old supplement commercials euphemistically would tout. Over the past few years, researchers have shown in numerous studies that eating more dietary fiber can provide a host of other benefits. Fiber in foods such as whole grains, fruits, and vegetables can reduce colorectal cancer, coronary heart disease, diabetes, obesity, and perhaps other ills.

But while studies supporting fiber’s benefits have blossomed, the average American’s intake of the nutrient has waned. Most people in the United States eat only half the recommended 20 to 35 grams of fiber a day, according to the American Dietetic Association.

One practically painless way to boost fiber consumption might be to increase the fiber content in the foods that people typically eat. That’s the idea behind a new study by a team of researchers in Australia and England. In the March 7 Proceedings of the National Academy of Sciences, the researchers detail how they genetically modified wheat to have about triple the usual amount of a dietary-fiber component called amylose.

Bulk up

Amylose is a type of starch called “resistant” because it resists digestion until it hits the large intestine. There, normal gut bacteria ferment this nutrient, releasing several health-promoting chemicals in the process. For example, lactic acid from the bacteria increases the acidity of the large intestine, which aids in killing off other bacteria that could make a person sick. Another bacteria-secreted chemical, called butyrate, seems to have roles both in preventing colon cells from turning cancerous and in lowering a person’s cholesterol.

Amylose is normally present in wheat, but in low quantities. That’s because enzymes in wheat plants chop most freshly made amylose molecules into smaller molecules, called amylopectin. That fiber gets digested before it reaches the large intestine and so is less valuable to the body than amylose is.

“You go from having a molecule which is like a long piece of string into something that looks like the fingers on your hand, a highly branched structure. It means water molecules and digestive juices can get in and break [amylopectin] down,” says Matthew Morell, a plant biologist at Commonwealth Scientific and Industrial Research Organization, a government research group in Australia.

To increase the amount of amylose in wheat, Morell and his colleagues knew that they had to prevent wheat’s enzymes from breaking down the molecule. In earlier studies, researchers succeeded in boosting amylose content in rice and corn by turning off a gene called starch-branching enzyme II b (SBEIIb). Initially, Morell’s team focused their efforts on blocking the effects of the same gene in wheat. However, the resulting wheat plants produced kernels with only marginally higher amounts of amylose than normal.

Through trial and error, the team found that turning off a related gene, called SBEIIa, had the desired effect. These new wheat plants produced kernels with about 74 percent amylose—compared with the 25 percent in regular wheat.

Resisting disease

Morell’s team didn’t stop at making the new high-fiber grain—they tested it to see whether it conferred some of the known benefits of amylose. He and his colleagues fed young rats diets containing either the high-amylose wheat or regular wheat for 13 days. During that time, the researchers kept track of the animals’ weights and analyzed the chemical contents of their feces for markers of bowel health.

They found that all the animals gained the same amount of weight, regardless of which wheat they ate. However, the stools of rats eating the high-amylose wheat were more acidic and had almost twice the amount of butyrate as the stools of rats eating regular wheat.

Co-author David Topping says that as best as the researchers could tell, the animals fed the modified wheat relished it just as much as the other rats enjoyed eating regular wheat. He adds that taste will certainly be a consideration if people get to try high-amylose food. “It’s no use creating this product if people won’t eat it,” he points out.

However, Morell’s team won’t be feeding people the genetically modified wheat that was in this experiment. Instead, the researchers plan on using their new knowledge to find other wheat plants with natural mutations that affect the SBEIIa gene and then propagate such a strain. Once farmers can grow such plants on a large scale, consumers could have ready access to high-amylose wheat in any product made with wheat flour, such as breads, pastries, and breakfast cereals.

“It’s an intriguing idea because consumers don’t have to do anything differently” to increase their fiber intake, says Mark Kantor, a professor of nutrition at the University of Maryland. “Nutritionists are constantly telling people to eat more fruits and vegetables, but people don’t want to change their eating habits because it’s just too hard. Here, they don’t have to change their eating habits because what’s being changed is the food they would normally eat anyway.”