Read up on gluten sensitivity... on of the primary ways gluten affects people with the sensitivity is by triggering an auto-immune (against one's own tissues) reaction against nerves and brain... so, now ask yourself, if gluten can trigger your own immune system to attack YOUR OWN nerves and BRAIN tissues due to misidentification by the antibodies, between the proteins in your own brain tissues, and gluten proteins... would that be considered 'STRESS' in the BRAIN? An intangible attack on one's own brain tissues by one's own antibodies -- how's that NOT stress? The cross-reactivity that gluten sensitivity can be triggered by other things which contain no gluten as well. Google gluten cross-reactive foods. Coffee is one, dairy, eggs, soy, rice, corn. It's because the immune system doesn't check the entire protein. So it can misidentify other proteins as invaders as long as enough of the protein is similar. A gluten sensitive person's auto-immune reaction can be triggered by other proteins which are similar.
So, if something is attaching your brain/nerves/tissues, how does it NOT make sense that there could be some visceral intangible 'anguish' / stress that would cause one to be tense, and grind ones teeth? Bruxism.