Humans and other animals have something called an opioidergic system – an evolutionarily-preserved way for an organism to modulate behavior, addiction, and reward. When you exercise, for example, a lot of the euphoria you feel comes from endogenous (produced in-house) opioids interacting with your opiate receptors. This is the body’s way of dealing with a stressful experience (physical exertion), reducing pain, and it also has the effect of reinforcing a behavior that is in the organism’s best interest.
The opioidergic system also interacts with the immune, endocrine, and central nervous systems (in other words, this is physiology, so it’s all interrelated), but we won’t get too much into that today. Now, it’s not just endogenous opioids interacting with our receptors; certain substances, like heroin and other opiate drugs, act as exogenous (produced out-of-house) opioids, thereby hijacking and “supercharging” our physiology. Cocaine, alcohol, and tobacco also interact with opioid receptors. The addictiveness of these substances is infamous, so these interactions exist shouldn’t surprise you.
However, there are other exogenous opioid peptides, also known as exorphins (exogenous morphine), found in substances that we don’t normally consider to be repositories of potentially addictive morphine-analogs. Like wheat.
Some of the most extensively studied food-based exorphins – gluten exorphins, from gluten, and gliadorphins, from gliadin – are derived from wheat. Are these exorphins actually problematic? Do they really interact with your opioid receptors to make you crave another “hit”? Well, an early 1979 paper (PDF) on the topic suggests that in order for them to actually function as in vivo opioid exorphins in our bodies, wheat exorphins must appear in our gastrointestinal tract after ingestion and during digestion, they have to survive degradation by intestinal enzymes into constituent amino acids, they have to be absorbed – intact – into the bloodstream, and they must pass the blood-brain barrier.
