WASHINGTON — The Food and Drug Administration on Aug. 2 reopened the comment period for its 2007 proposal on labeling foods as “gluten-free.” The agency also made available a safety assessment of exposure to gluten for people with celiac disease and invited comment on the additional data.

People who have celiac disease cannot tolerate gluten, a protein in wheat, rye, and barley. Celiac disease damages the small intestine and interferes with absorption of nutrients from food. About 1% of the U.S. population is estimated to have the disease. Having a single federal definition of “gluten-free” was considered critically important in assisting individuals with the disease select a healthful diet.

“Before finalizing our gluten-free definition, we want up-to-date input from affected consumers, the food industry, and others to help assure that the label strikes the right balance,” said Michael Taylor, the F.D.A.’s deputy commissioner for foods. “We must take into account the need to protect individuals with celiac disease from adverse health consequences while ensuring that food manufacturers can meet the needs of consumers by producing a wide variety of gluten-free foods.”

The F.D.A.’s Center for Food Safety and Applied Nutrition in May 2011 published a report titled “Health hazard assessment for effects of gluten exposure in individuals with celiac disease: Determination of tolerable daily intake levels and levels of concern for gluten.” The F.D.A. indicated a reason for reopening the comment period for “gluten-free” was to encourage comments on the data it contains, including whether that data should affect the final rule on “gluten-free” labeling, and if so, how.

The chief criterion proposed in 2007 and that the F.D.A. upholds going into the new comment period is that foods bearing the claim “gluten-free” may not contain 20 parts per million (p.p.m.) or more gluten. The agency based the proposal, in part, on the available methods for gluten detection. The validated methods may not reliably detect the amount of gluten in a food when the level was less than 20 p.p.m. That remains the case today.

The threshold of less than 20 p.p.m. is similar to “gluten-free” labeling standards used by many other countries, including Japan and the European Union. The proposed limit also conforms to the standard set by the Codex Alimentarius Commission in 2008, which requires that foods labeled as “gluten-free” not contain more than 20 p.p.m. gluten.

The F.D.A. also indicated it was concerned that adopting a threshold lower than the less-than-20-p.p.m. limit for a “gluten-free” claim might have “the unintended and unwanted effect of making it more difficult for those with celiac disease to adhere to a lifelong ‘gluten-free’ diet, thereby putting those at risk of developing serious health complications and other diseases associated with celiac disease.”

The agency’s concern was based on questions relating to whether manufacturers of multi-ingredient foods, especially grain-based foods, would be able to comply with a gluten threshold much less than 20 p.p.m. The F.D.A. asserted it did not want food manufacturers to discontinue labeling their products “gluten-free” because they cannot consistently and reliably meet an even lower gluten threshold, nor did it want to discourage other companies from becoming manufacturers of foods labeled “gluten-free” because of a lower threshold. The F.D.A. also sought to avoid a significant increase in the cost of foods labeled “gluten-free,” and it was wary of negatively affecting international trade in foods labeled “gluten-free,” which may affect the availability of certain foods to those individuals with celiac disease.

At the same time, the F.D.A. requested comments regarding whether the possible presence of more than 0.01 p.p.m. but less than 20 p.p.m. gluten in a food bearing a “gluten-free” label claim would be a material fact that must be disclosed on the label in order to prevent a “gluten-free” claim from being false or misleading.

“For example, an asterisk could be placed immediately after the term ‘gluten-free’ on the food label or in the food labeling with a clarifying statement located in close proximity to that claim in a print size no smaller than one-sixteenth of an inch (e.g. ‘does not contain 20 p.p.m. or more gluten’ or ‘does not contain 20 micrograms or more gluten per 100 grams of food’),” the F.D.A. said.

Additionally, the F.D.A. said it recognized there are highly sensitive individuals among those with celiac disease who may not be fully protected if they consume foods containing a trace level of gluten above 0.01 p.p.m. but below 20 p.p.m. The agency sought comments on whether a “gluten-free” claim based on a less-than-20-p.p.m. threshold should be accompanied by a qualifying statement because of this reason.

The F.D.A. said it also would find it helpful to again solicit comments about any reasons that would support a gluten threshold level to define, in part, the food labeling claim “low gluten.” This would be in addition to, not in place of, a definition of “gluten-free” for product labeling.

“If such reasons exist, F.D.A. is also seeking comments on the specific gluten threshold level and any other criteria the agency should use to define the term ‘low-gluten,’” the agency said.

The F.D.A. encouraged all

interested parties to offer com-ments and suggestions about gluten-free labeling in docket number FDA-2005-N-0404 at www.regulations.gov. The docket opened for comments on Aug. 3, 2011, and will remain open for 60 days after that date.