CHICAGO — The Food and Drug Administration has cleared up some confusion by listing what isolated or synthetic carbohydrates the agency will allow to be labeled as fiber in food products.

Yet the listing has created confusion in another fiber area. No such list exists for intrinsic and intact carbohydrates that might qualify as fiber on labels, and debate has focused on what qualifies as intrinsic and intact.

The listings have become important to ingredient buyers at food companies, said George Salmas, managing principal for The Food Lawyers in Los Angeles. The buyers are asking suppliers if their ingredients are on “the list,” wanting to make certain they legally can count the ingredients as fiber in the Nutrition Facts Label of food products.

“They’re buyers,” Mr. Salmas said July 18 at IFT18, the Institute of Food Technologists’ meeting and food exposition in Chicago. “They don’t want to get sued. They want a simple answer, and the simple answer is to be on the list.”

Ingredient suppliers, however, need other ways of proving intrinsic and intact carbohydrates qualify as fiber. Mr. Salmas gave examples of how F.D.A. documentation could prove the agency views an ingredient as fiber. Documentation may be found when the F.D.A. offers guidance or when it responds to public comment in the Federal Register.

“I read that commentary,” Mr. Salmas said. “I get so much out of that because someone in the industry is asking a question, and the F.D.A. is telling them how they feel.”

If the F.D.A. responds favorably to an ingredient, such as by saying it views the ingredient as fiber, “you’ve got something from the F.D.A. in writing that says you qualify,” Mr. Salmas said.

The F.D.A. defined fiber for the first time in the May 27, 2016, issue of the Federal Register as non-digestible soluble and insoluble carbohydrates (with three or more monomeric units), and lignin that are intrinsic and intact in plants; and isolated or synthetic non-digestible carbohydrates (with three or more monomeric units) determined by the F.D.A. to have physiological effects that are beneficial to human health.

Determining intrinsic and intact has been a challenge, said Paula R. Trumbo, Ph.D., a supervisor for the F.D.A.’s Center for Food Safety and Application Nutrition.

The F.D.A. followed the Institute of Medicine’s “intact” definition: having no relevant component removed or destroyed.

“Well, what does relevant mean?” Dr. Trumbo said in giving a question that companies and the F.D.A. need to answer.

The F.D.A. also followed the I.O.M.’s “intrinsic” definition: originating and included wholly within a food.

“It gets really tricky,” Dr. Trumbo said. “Well, how much processing is involved such that it is no longer intact and intrinsic?”

The F.D.A. in giving an example said it considers brans to be intrinsic and intact because brans are anatomical layers of the grain consisting of intact cells and substantial amounts of starch, protein and other nutrients.

The F.D.A. also gave an example of an ingredient not being intrinsic and intact: resistant starch that has been extracted and isolated from the flaked corn cereal such that it is no longer part of the food matrix (intrinsic) and no longer consists of relevant food components (intact). In this example the ingredient would be an isolated or synthetic carbohydrate.

The F.D.A. in the May 27, 2016, issue of the Federal Register began listing isolated or synthetic carbohydrates that it viewed as fiber.  Making the list at that time were beta-glucan soluble fiber, barley beta-fiber, psyllium husk, cellulose, guar gum, pectin, locust bean gum and hydroxypropylmethylcellulose.

This year in the June 15 issue of the Federal Register the F.D.A. listed eight more isolated or synthetic carbohydrates that it would allow to be labeled as fiber: mixed plant cell wall fibers, arabinoxylan, alginate, inulin and inulin-type fructans, high-amylose starch (resistant starch 2), galactooligosaccharide, polydextrose, and resistant maltodextrin/dextrin. Mixed plant cell wall fibers must contain two or more of the following: cellulose, pectin, lignin, beta-glucan and arabinoxylan.