Gluten is a protein found in wheat, barley and rye, and people with celiac disease or gluten intolerance need to eliminate it from their diet to prevent illness. While some weight-gain supplements may contain gluten, you should be able to find a number of gluten-free options to meet your needs.
Check the Food Label
When looking for gluten-free weight-gain supplements, the food label is a good place to start. In 2014, the U.S. Food and Drug Administration issued a ruling allowing food manufacturers to clearly label their food items as gluten-free if they are inherently free of any gluten-containing ingredient.
However, the gluten-free labeling is voluntary, so even if a weight-gain supplement is not labeled as gluten-free, it might still fit into a gluten-free diet. Use the ingredients list to figure it out. Avoid any supplements that contain the words wheat, barley, rye, starch, flour, malt or triticale.