To comply with the U.S. Food and Drug Administration's regulations, foods that carry the gluten-free label must contain less than 20 parts per million of gluten. Metamucil Powders, Fiber Singles, Capsules and Clear & Natural are all gluten-free, but Metamucil Wafers are not.
The FDA announced its gluten-free standards in August 2013, giving manufacturers a deadline of Aug. 5, 2014 to comply. The maximum of 20 parts per million was established because it is the lowest level of gluten that can consistently be detected in food. While sensitivity levels vary, most people who suffer from celiac disease can tolerate this trace amount of gluten.
"Gluten-free" can also refer to foods that do not contain wheat, barley, rye or crossbreeds, whether they have been processed to remove gluten or inherently do not contain the protein. The FDA does not regulate non-packaged foods served in restaurants.
Metamucil is a laxative and fiber supplement. The gluten-free forms are sold as powdered drink mixes or capsules, available in various flavors. Its primary active ingredient is psyllium seed husks. While regular use of Metamucil has been linked to lowered cholesterol levels, use of fiber supplements carry the risk of decreasing the absorption of nutrients through the gastrointestinal tract, leading to malabsorption issues in people who do not or barely meet their minimum nutritional requirements.