COLLEGE STATION — Dr. Joanne Lupton is dedicated to the proposition that not all dietary fibers are created equal, and she hopes her newest five-year research program helps prove that point to consumers and the government.
One of the Texas Agricultural Experiment Station researcher’s goals is to increase public understanding of the roles of various fibers. Included are seemingly conflicting roles as both promoters of and protection against colon cancer — depending on the type of fiber and the circumstances under which it is consumed.
“One fiber is as different from another as vitamin A is from vitamin B12,” said Lupton, who is an associate professor of animal science at Texas A&M. “Each has its benefits, but each can be misused.”
For instance, soluble fiber appears useful for lowering serum cholesterol in the blood, which in turn lowers the risk of heart disease. Soluble fiber, such as oat bran, is more easily dissolved and fermented during digestion.
But that same fiber evidently may trigger mechanisms that promote colon cancer in some cases, while insoluble fiber, such as wheat bran, appears to protect against colon cancer, Lupton said.
There appears to be a relationship between highly fermentable fiber and the enhancement of tumor growth, and Lupton and her colleagues hope to find out why.
Their current research, funded by the U.S. Department of Health and Human Services, seeks to understand the mechanisms by which various fibers work.
The department will provide $850,000 over five years to Lupton and three other co-principal investigators — Drs. Robert Chapkin and Guoyao Wu of the animal science department and Dr. Robert Burghardt of Texas A&M’s veterinary school. The four will work with a number of graduate students and others on the project over the five-year period.
Their work will focus on short-chain fatty acids, or SFCAs, which are products of fiber fermentation. They want to find out how those fatty acids change the biochemistry of cells in the colon after being taken into the cells.
Three fatty acids make up between 90 and 95 percent of the SFCAs in the colon — acetate, propionate and butyrate. All stimulate growth in the body for both normal and cancerous cells, but butyrate appears also to inhibit the growth of tumors in artificial cultures.
The primary questions the team will seek to answer, Lupton said, are what colonic cells do with butyrate and how diet impacts that process, as well as whether cell use of butyrate differs between cancerous cells and normal cells.
“We have good reason to believe butyrate use differs because of the evidence we have about it in cultures,” Lupton said. “We need to examine whether we’re overlooking something when we move from an animal to a test tube, or whether butyrate just works differently in normal, healthy cells.”
Lupton said it should take about two years for the study — which began in late 1993 — to show whether there is a difference in cell metabolism, then another year to evaluate tumors for confirmation of that difference. Yet another year will be required for statistical evaluation of data they obtain.
The team will also examine whether differences in diet or timing of SFCA use by cells makes a difference in development of cancer cells.
Such knowledge will go a long way toward helping consumers be aware of benefits and drawbacks to various types of fiber.
For now, she recommended, “if consumers just follow the recommendation to increase the proportion of naturally fiber- bearing foods in the diet, that’s a good general approach. But all bets are off when you change the natural proportions. As a consumer, you are then getting fiber not from foods, but from food supplements.”
Many fruits, vegetables and grains are among the naturally fiber-bearing foods, and some foods contain both soluble and insoluble fiber.
Lupton’s expertise made her part of a panel of experts who will participate in a May 12-13 conference on the role of fiber in cancer and cardiovascular disease. The conference, to be held in Rockville, Md., is sponsored by the Food and Drug Administration.
The conference’s goal is to foster debate among scientists about methods used to assess fiber’s role and to find standards for scientific agreement to help set federal regulations on advertising claims regarding fiber.
Regardless of the conference’s outcome, Lupton expects her latest project to be just another major step on the path to understanding dietary fiber.
“It’s a five-year grant,” she said, “but it’s something I plan on spending the rest of my academic lifetime on.”
Fiber’s foothold in a healthy diet
The everage consumer eats only 12 grams of dietary fiber per day, far less than the 25-35 grams recommended by nutritionists. Fiber-filled foods, rather than fiber supplements, should be the source of dietary fiber. Breads, cereals, fruits and vegetables are good sources of fiber.
|fiber in grams
|corn kernels-2/3 cup
|dry grits-1/2 cup
|kidney beans-1 1/3 cup
|parsnip-1 3/4 cup
|potato, cooked-3/4 cup
|rolled oats, dry-1 cup
|shredded wheat-4 biscuits
|whole wheat bread-1 slice