Dr William Davis claims that the protein gliadin in wheat (at least, strains grown since the '60s or so) stimulates appetite, leading to obesity. He has released a book on the topic, called Wheat Belly: Lose the Wheat, Lose the Weight, and Find Your Path Back to Health. His claims (including a video) are described in a CBS report:
This thing has many new features nobody told you about, such as there's a new protein in this thing called gliadin. It's not gluten. I'm not addressing people with gluten sensitivities and celiac disease. I'm talking about everybody else because everybody else is susceptible to the gliadin protein that is an opiate. This thing binds into the opiate receptors in your brain and in most people stimulates appetite, such that we consume 440 more calories per day, 365 days per year
In an article on BlissTree, Elizabeth Nolan Brown disputes Dr Davis's claims:
Lie #1: Gliadin is a ”new protein” being engineered into wheat. Actually, gliadin has always been in wheat.
Lie #2: Gliadin is an appetite-expanding opiate. Giadin[sic] is not actually an opiate. Gliadin polypeptides can bind to opiate receptors in the brain, but there’s no evidence that this stimulates appetite
Her claims about the origins of gliadin are not well referenced, and she doesn't consider the quantity.
The Grain Foods Foundation have also disputed the risks of gliadin:
Cutting out one specific food is not only unrealistic, it’s dangerous. Omitting wheat entirely removes the essential (and disease-fighting!) nutrients it provides including fiber, antioxidants, iron and B vitamins.
Besides this, the advice dished out by Dr. Davis is completely counter to the Dietary Guidelines for Americans, the gold standard of scientifically-sound nutrition advice. The Guidelines call for the average healthy American to consume six one-ounce servings of grain foods daily, half of which should come from whole grains and the other half from enriched grains. Wheat is the basis for a number of healthful whole and enriched grain foods including breads, cereal, pasta and wheat berries that provide valuable nutrients to the American diet and have been shown to help with weight maintenance.
Has wheat been modified to introduce gliadins? Do they act as opiates to increase appetite?