I am very pleased to present a guest post, created by Elizabeth, a subscriber and frequent contributor to my home blog: http://www.memoirsofanaddictedbrain.com/blog/. Elizabeth's understanding of eating disorders comes both from experience and from her expertise in the neuroscience of addiction. I feel a lot of affinity for her thoughts and feelings, since my interest in drug addiction also comes from both personal experience and scientific study.
The present “obesity epidemic” has given rise to public concern about the level of refined sugars, including high-fructose corn syrup, in the North American diet. But is overconsumption of sweet and calorie-dense foods really a kind of “addiction”? One way to find an answer is to examine parallels with drug addiction. What do these two phenomena have in common?
Several years back, researcher Roy Wise argued that drug intake could be viewed as an “ingestive behavior.” He noted that animals who were limited to short periods of drug availability throughout the day showed signs of “regulated drug intake” to maintain a steady blood serum level, similar to “regulated food intake” to maintain energy balance. When these trials were ended, the animals displayed little, if any, signs of withdrawal. Thus, they were probably not really addicted or dependent on the drug at all.
What might change this pattern of "regulated" intake? In other words, where, if anywhere, is the switch between ingestion and addiction?
As discussed in this blog and elsewhere, precursors to drug addiction in humans include high stress, anxiety, depression, and social isolation. Yet similar factors aid the development of “addiction-like” drug intake in animals. When exposed to stress or social isolation, rodents with a
steady, regulated pattern of intake can be shown to escalate their consumption, pursue the drug in the face of punishment, and show physiological withdrawal symptoms. In other words, some kind of social-psychological challenge pushes these animals over the line from consumption to addiction.
Indeed, the ingestion of foods can also be viewed as normal, versus addictive, depending on social-psychological factors, and many of these factors are well recognized. Stress, depression, and negative self-worth play major roles in the development of eating disordered behavior, including excessive caloric restriction, binge food intake, purging, and so forth. Then perhaps we should look for a common neural mechanism that underlies the switch from consumption to addiction in both humans and animals, drugs and food.
Food and drug rewards act on the same neurotransmitter systems, so disruptions in reward circuitry that can confer drug addiction would theoretically change the meaning of food. So here's a phenomenon that points directly to a switching mechanism. If you want to get an animal to REALLY want to take a drug, you can deprive it of food, and some of the same neurochemicals that induce food-seeking behavior in hungry animals also invigorate drug-seeking behavior. This suggests that deprivation, or "dysregulated food intake," is one way to trigger the switch into the craving state, and in doing so it cross-sensitizes with drug intake (like how abuse of one substance can lead to abuse of another). Basically, since the brain interprets the value of both food and drug rewards through similar circuits, primarily fueled by the neurotransmitter dopamine, alterations in these circuits can cause excessive pursuit of both. The brain is saying “hey, I’m deprived of some necessary sustenance…give me more! The next time I get that reward, it’s going to be REALLY reinforcing, so I will seek it harder and make sure I get all I can!” So, the next time drugs are encountered, we binge on them. The next time we get access to a sweet treat, we are likely to binge on that as well. In fact, there is a striking comorbidity between binge food intake and drug abuse.
What this means is that there can be addiction-like components to both binge eating and drug taking. The super-sensitivity to both rewards appears to be greatly influenced by the individual’s history: Have there been significant life stressors? Has the individual been deprived either psychologically or physiologically? Anorexic and bulimic patterns for coping with stress actually cause physiological deprivation. So these disorders sew the seeds of their own recurrence. What these conditions have in common is that a number of stress-inducing factors come together to promote a sort of “super-craving”—for food, drugs, or both.
I’m not sure that these psychological and neural mechanisms are widespread enough to completely explain the obesity epidemic. But they can certainly explain how some people slip over the edge from a balanced pattern of eating to one that becomes dysregulated, chaotic, and even desperate.