How is Gluten Digested?
To fully understand gluten-intolerance, it is necessary to have an understanding of how gluten is digested. Then, how that digestion results in pain.
In the gut, protein digesting enzymes are secreted (1). These enzymes will come from the stomach, walls of the small intestine, and the pancreas (2,3). With most proteins, enzymes break down the protein into single amino acids, or small di- or tri- amino acids (4).
Glutenin, the first protein in the gluten-matrix, is digested by these enzymes easily because it is a long protein with a great amount of surface area for the enzymes to attach and degrade (5). However, Gliadin, the other protein, is a densely packed protein with a low surface area to volume ratio (6, 7), making it difficult for enzymes to encounter. In addition, gliadin protein has a large amount of amino acids that are especially difficult to digest. These difficult to digest amino acids are proline and glutamine (8).
As such, naturally occurring protein digesting enzymes have difficulty degrading gliadin (9). Due to the difficulty protein-digesting enzymes have with gliadin, gluten is digested into long amino acid chains, called oligopeptides, rather than the di- or tri-amino acids that otherwise occur with normal protein digestion.
As observed through antibody assays, an inflammatory response is created during gluten digestion because of these oligopeptides (10). The body mounts an attack on gliadin, degraded gliadin, and the enzyme that helps in gliadin digestion, transglutaminase (11), as observed through diagnostic antibody assays (12) . This inflammatory response is not localized to the small intestine, but, rather, it is a systemic inflammation response, as identified by human sera antibody levels (13).
Therefore, gluten results in pain to a gluten-intolerant individual because of the systemic inflammation resulting from the difficulty that protein digesting enzymes have with the gliadin, and other members of the prolamin family of grain proteins.