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Humboldt Field Research Institute

Posted April 5, 1999

Defining Dietary Fiber No Easy Task

It's not one of the basic food groups, but fiber has become a dietary icon. Magazines and talk show hosts extol its virtues, and the federal Food and Drug Administration recommends eating foods high in fiber to reduce the risks of cardio-vascular disease and colorectal cancer. Nevertheless, the research record contains a few surprises for consumers, says Mary Ellen Camire of the University of Maine's Department of Food Science and Human Nutrition.

The truth about fiber is shrouded in controversy and conflicting studies. In recent years, doubts have been cast on the colorectal cancer fighting benefit of fiber by three major reports that concluded that a high fiber diet did not lower cancer rates. Nevertheless, fiber's reputation still stands for other health benefits. Researchers have demonstrated that fiber can reduce risks of heart disease, hypertension, non-insulin dependent diabetes and a bowel problem known as diverticulitis.

Nutrition is a young science

New experiments by Camire and her students are helping consumers, food processors and government agencies put fiber in proper perspective. “Nutrition really was born this century. People don't realize, for example, that we discovered the vitamins during the past century. We didn't realize the role of fiber in food until the 1960s. The science is young and still evolving,” Camire says.

Camire has been studying dietary fiber since her graduate student days at Texas Woman's University in Dallas during the late 1980s. For her Ph.D. dissertation, she studied fiber in corn-based snack foods. After coming to UMaine, she began working on new methods to analyze foods for fiber content.

Such fundamental work is timely because the FDA and the food processing industry do not have a single, comprehensive definition for the term “fiber.” “When we first started realizing there were health benefits to fiber, we were measuring crude fiber. We took a food, boiled it in acid, then boiled it in alkali and whatever was left, you said it was fiber. But our bodies don't work that way. Now, we're trying to do things that imitate the body. This is a big controversy,” Camire explains.

In laboratory studies, she focused on potato peels which, she demonstrated, can perform like champions in the colon by binding with potential cancer causing compounds and escorting them out of the body.

As part of a group working through the American Association of Cereal Chemists (AACC), Camire helped to develop the modern fiber analysis method which has been adopted world-wide. It is a complicated, time consuming procedure and a major step forward, but it is still not perfect. It still leaves some compounds unmeasured, such as indigestible long-chain sugars which behave like fiber.

Today, Camire is working with an AACC committee to devise a single definition for fiber. Interviews are being conducted with academic scientists, industry researchers and government regulators and hope to complete their work by the fall of 2001.

Fiber and phenolics

Just as important, some of the benefits attributed to fiber may actually be linked to associated compounds known as phenolics. In research published in 1995 in the Journal of Agricultural and Food Chemistry, Camire and her UMaine colleagues Jianxin Zhao, Michael P. Doherty and Rodney Bushway showed that these chemicals also help bind benzo(a)pyrene, a common cancer causing agent in food.

“We're just starting to realize that phenolics are in our foods in gram quantities daily, but we've sort of ignored them,” says Camire. “We don't need them to grow. Your hair doesn't fall out if you don't have them. All plant foods have phenolics and some forms are soluble. You get them in fruit juice. It's a separate class of plant molecules.

“It just happens that the way plants grow, phenolics are entwined with fiber molecules. And now we're wondering how much of the benefit of fiber is due to fiber and how much to what's with the fiber. We're seeing more and more work being done on the health benefits of phenolics.”

In 1997, Camire received a $49,316 grant from the U.S. Department of Agriculture to study the potential for phenolic compounds to prolong the shelf-life of extruded corn snacks and breakfast cereals. As anti-oxidants, phenolics can slow the breakdown of fats and also reduce the generation of free radicals which can lead to cancer.

Hannah Osborn, a Junior from Big Piney, Wyoming, and Ken Viscidi of West Virginia, a Master's student, are expanding those studies to determine if phenolics can affect carbohydrates and the balance between soluble and insoluble fiber in processed foods. That's no small matter for the food industry, Camire notes. Some food production processes such as extrusion can tilt the scales in favor of soluble compounds. Unlike the insoluble forms, soluble fiber may contribute to colorectal cancer by releasing irritating bile acids in the colon.

From the industry's point of view, any production process which leads to demonstrated health benefits can become a new marketing point as well as a health benefit for consumers.

After Camire's 1995 articles were published, industry representatives called her frequently. Camire still gets one or two calls a month from food processors who want to discuss methods for increasing the fiber content of their products.

On the horizon for faculty and students in the department are new studies to identify all of the fiber compounds in breakfast cereals and determine how processing can enhance their benefits. Ultimately, Camire would like consumers, food processors and government regulators to have accurate information about how much fiber and phenolics are in the typical American diet and how they behave in our bodies.

“Right now,” she says, “the FDA doesn't have accurate fiber values for a lot of foods. It's just ballparking. We could be very much over or under estimating people's fiber intakes. In regard to such a fundamental part of our diet and human health, we have to have better data to help consumers.”

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