It is common to hear claims in the vegan community that milk & cheese are literally addictive and contain a morphine-like substance, for many this factoid has become so ubiquitous that it is generally taken as an accepted scientific truth. But what is the actual evidence for this claim?
One of the main proponents of this claim is Dr Neal Barnard who heads up the Physicians Committee for Responsible Medicine (PCRM). Barnard has gone so far as to claim that cheese “can be as addictive as morphine” and referred to it as “dairy crack”. Barnard’s premise in Breaking the Food Seduction is that not only is the food addiction model correct (still a contentious issue in itself) but that it is not, as hypothesized, merely due to endogenous biochemicals acting on reward pathways in the brain but also due to the fact that many foods such as dairy, chocolate, and meat contain addictive chemicals themselves and can induce food-specific addictions, such as a “cheese addiction”. As evidence of the addictive potential of cheese Barnard cites the presence of exogenous opioid peptides, or exorphins,
“Cow’s milk-or the milk of any other species, for that matter-contains a protein, called casein, that breaks apart during digestion to release a whole host of opiates, called casomorphins.”
To demonstrate the addictive power of food Barnard cites research in which Naloxone, an opioid antagonist, caused a loss of interest in the food being studied. Bardnard would like us to believe that “cheese’s popularity may have less to do with its meltability and mouth-feel and more to do with its addictive qualities.” Unfortunately for him the Naloxone research he cites contradicts this claim. The studies most cited were investigating chocolate, sweets, and fats and opioid antagonists like Naloxone reduce cravings for all of these. Far from establishing the role of casomorphin in the appeal of cheese, studies done with Naloxone point more to the importance of general palatability. In other words it may not be the presence of specific psychoactive chemicals that we find so compelling about certain foods but rather the overall sensory appeal of the food.
Placebo controlled research on chocolate addiction for example found “no role for pharmacological effects in the satisfaction of chocolate craving”, rather it found that sensory aspects were more likely the primary factor. Research on casomophin also found that it did not demonstrate “reinforcing properties similar to those of morphine” and concluded that “beta-casomorphin is not likely to become the focus of an addiction.” While there is evidence that the endogenous opioid system plays some role in food intake and craving, the problem comes in when people such as Barnard try to make it appear that it is more due to the effects of specific exogenous opioids rather than the complex interactions of mostly endogenous biochemicals and when the case is overstated with extreme claims and hyperbole.
Dairy isn’t the only source of exogenous opioid peptides however. There are a variety of other opioid peptides in various foods such as hemorphins derived from hemoglobin (a component of blood), gluteomorphin from gluten, rubiscolin derived from spinach, and even soymorphins derived from soy. One study even found that soymorphins “showed opioid activity more potent than human beta-casomorphins”, at least on guinea pig ileum. If Barnard’s theory is true we might expect similar addiction patterns for these foods. While there are claims among some that products containing gluten are addictive, this is also still scientifically controversial and is even approached warily by other anti-wheat writers. One would also expect that if gluten does have this effect that vegans would be a high risk population as they are the most likely to consume relatively large amounts concentrated gluten in the form of seitan. While seitan is quite yummy when prepared well, I don’t think many would describe it as literally addictive. The case of soymorphin is also quite interesting, these peptides should be ubiquitous in the diets of many vegans, though there is still little concern over a tofu addiction. Perhaps casomorphin does have an effect that would elicit casein-specific cravings, however it appears from the current research that if this effect does exist that it is so far indistinguishable from food cravings for any other high preference food.
Is cheese really addictive? by Diana of The Vegan Option
Vegan Cheese: Casein, Casomorphins, and the Daiya Redwoods Vegusto Taste Test on The Vegan Option podcast
Review of the potential health impact of β-casomorphins and related peptides European Food Safety Agency (2009)
Chocolate: The news you wanted to hear by Glenn Cardwell
The plausibility of sugar addiction and its role in obesity and eating disorders.