Zein is a protein in corn (“maize” outside the U.S.) that, if held side-by-side against the gliadin protein of wheat, rye, or barley, overlaps substantially in structure (i.e., amino acid sequence).
In other words, the zein protein of corn resembles the gliadin protein of other grains—not identical but with overlapping similarities in structure. This should come as no surprise, as corn and other grains share evolutionary history as grasses, not to mention ongoing exchange of genetic material over eons, given the impressive promiscuity of grasses and their ability to share and combine genetic material. (Recall how 14-chromosome ancient einkorn wheat mated with various wild grasses over the last several thousand years to yield modern 42-chromosome Triticum aestivum wheat.) Zein and gliadin are examples of prolamin proteins, a class of proteins in grasses. They are called prolamins because they are unusually rich in the amino acid, proline.
Zein represents nearly half the protein in corn. (Beyond proteins, the remaining constituents of corn are largely carbohydrate-fibers, amylopectin and amylose. This explains why, when corn is reduced to a powder, as in corn meal or cornstarch, the glycemic index is the highest of any food, and why corn is used to make high-fructose corn syrup. Yes: corn is a flagrant contributor to high blood sugars, insulin resistance, inflammation, visceral fat accumulation, type 2 diabetes, and all the unhealthy phenomena associated with protein glycation.) And, given the extensive similarities among prolamin proteins in grasses, proteins closely resembling zein are also present in millet and rice.
Among the observations made with the zein protein of corn are:
- As with gliadin that is incompletely digestible by humans because we lack digestive enzymes that disrupt proline-rich sequences, so the proline- and cysteine-rich content of the zein protein also resists human digestion (Ortiz-Sanchez 2013), just as you’d expect of proteins from seeds of grasses. Undigested proteins and polypeptides are notorious for triggering autoimmune diseases. In animal models, the gliadin protein of wheat powerfully provokes type 1 diabetes, and so does the zein protein (Mueller 2009).
- In people with celiac disease, we know that the zein protein stimulates abnormal immune responses, similar (though less intense) to that provoked by gliadin and that full reversal of celiac disease requires corn elimination in many, if not all, people (Sanchez 2015; Cabrera-Chevez 2008; Ortiz-Sanchez 2013; Kristjansson 2005; Vargas 2014). And just as the gliadin protein interacts with the HLA DQ-2 and DQ-8 genetic variants to trigger the immune response leading to celiac disease, so does the zein protein. In other words, corn contains no gluten—it contains a protein that overlaps in structure to gluten and has potential to stimulate some of the same abnormal immune responses as the gliadin within gluten. You may begin to appreciate the folly of “gluten-free” products made with cornstarch: While they do not contain gluten, cornstarch contains residues of zein that can mimic many of the effects of gliadin.
- Allergy to zein (as well as other corn proteins) occurs to extravagant degrees in people who are repeatedly exposed–This doesn’t happen with lettuce, cucumbers, beef or most other foods. Up to 90% of people who work in the pharmaceutical manufacturing industry, in which cornstarch and other corn-derived products are commonly used as ingredients in manufacturing tablets and capsules, develop allergies to corn (Valencia Zavala 2006). I believe that this phenomenon reflects the fact that corn is not something that humans should be exposed to or consume, something foreign to the human dietary script and daily experience. Recall that dietary allergies can show themselves as gastrointestinal distress, bloating, and diarrhea, as well as skin rashes, sinus congestion, and asthma.
So just because “zein” does not sound like “gluten” or “gliadin” does not mean that there are not shared characteristics of these proteins from seeds of grasses. This is why in the Wheat Belly lifestyle we are completely free of all components of the seeds of grasses whether from wheat, rye, barley, millet, or corn.