Celiac Disease and Non-Celiac Gluten Sensitivity
What Is Gluten?
Gluten is not a single protein but rather a complex mixture of proteins, primarily gliadin and glutenin. Gluten forms when wheat flour is mixed with water to make dough. The combination of gliadin, a viscous (thick) protein, with glutenin, a long, elastic protein, yields gluten with its unique “visco-elastic” properties that are important in baking and food processing (Veraverbeke 2002; Allred 2010; Shewry 2002; Tatham 2000).
Thus, despite the common usage of the term “gluten-containing grains,” gluten itself is not actually present in the wheat seed; it is created during the formation of wheat flour dough (Hoseney 1990; Shewry 2002; Tilley 2001).
Rye and barley, the other “gluten” grains, do not actually form gluten (Tatham 2000). Instead, secalin proteins in rye and hordein proteins in barley contain toxic fragments that share properties with the wheat protein gliadin, most notably with regard to triggering celiac disease (Kagnoff 2007; Denham 2013). For convenience and simplicity, all three grains—wheat, rye, and barley—are considered “gluten-containing grains.”
Gliadin (wheat), secalin (rye), and hordein (barley) proteins are especially rich in two amino acid “building-blocks,” proline and glutamine, and thus are called “prolamins” (Stenman 2010; Hausch 2002; Denham 2013; Stern 2000). The bonds linking proline and glutamine on the gluten protein are resistant to digestion. This prevents complete breakdown of gluten into small, harmless molecules. Instead, large, undigested gluten fragments remain in the digestive tract (van den Broeck 2009; Kagnoff 2007; Denham 2013; Gass 2007).
In healthy people, these large, undigested fragments of gluten protein are eventually harmlessly excreted and do not provoke an immune response (Fasano 2009). For people with celiac disease, however, these glutamine- and proline-rich fragments, or peptides, are toxic (Sapone 2011; Holmes 2013; Volta 2013; Shan 2002).