of the time. However, exposure to potentially dangerous
bacteria, especially in the small intestine, can cause the
junctions to loosen, drawing water and immune cells into
the gut lumen. This usually results in diarrhea to flush out
the troublemaker—a critical defense response during acute
infection.^20 Unfortunately, certain aspects of modern life
can also cause our gut barrier to be more porous and allow
for retrograde transport, or the transport of gut contents
deep into the gut lining. This leads to considerable
consequences and possibly initiates the “molecular
mimicry” that is thought to result in autoimmunity.
One possible instigator of undue permeability to the gut
lining is gluten, the protein found in wheat, rye, barley, and
many packaged foods. Gluten is unique among proteins that
we consume because unlike, say, the protein we get from
eating a chicken breast, gluten is not completely digested by
humans. Protein from most sources will separate into its
constituent amino acids during digestion, but gluten breaks
down only into large fragments called peptides. These
fragments have been found to stimulate a more permeable
gut in humans, triggering a welcoming from the innate
immune system more similar to that of a bacterial invader
than that of your usual dietary protein.
At the center of this response is another protein called
zonulin, which is produced in the gut whenever gluten is
present.^21 Zonulin acts as a cellular gatekeeper of sorts,
regulating the integrity of the tight junctions in between
epithelial cells. Where there is zonulin, there is permeability.
(Dr. Alessio Fasano, founder of Mass General’s Center for
Celiac Research and an internationally recognized expert in