Anorexia nervosa was first described in the medical literature in 1689 by Richard Morton. It has been over 300 years since then and AN continues to be one of the deadliest psychiatric disorders. If not treated early, it runs the risk of becoming deeply entrenched and highly resistant to treatment.
Moreover, established treatments for related disorders like bulimia nervosa and depression, such as cognitive behavioural therapy and antidepressants, are rather ineffective in treating anorexia nervosa. Finally, even if significant physical and mental improvements are achieved in treatment, relapse rates for older individuals (even those in their 20s) remain high.
What makes anorexia nervosa so persistent and so hard to treat in individuals who develop it, particularly if it is not treated soon after onset? Why is recovery so hard?
In this paper, B. Timothy Walsh outlines a model based on cognitive neuroscience that attempts to answer these questions:
Its central element is that this behavior has become habitual and is grounded in the neural mechanisms that underlie habit formation and persistence. This formulation is based on a substantial body of animal and human research, much of which is focused on the neural mechanisms underlying substance abuse.
DIETING AS A HABIT
I’ve often said that restricting to me feels like the “default state”: without continual conscious effort to consume more food, I can easily slip into restriction almost by accident. In a sense, restricting is a habit — a learned or acquired pattern of behavior that occurs without conscious effort and can be provoked by various stimuli (or triggers).
It is crucial to emphasize that this is not innate:
In order to lead to significant weight loss, the dieting behavior must be engaged in repeatedly, over weeks to months, and the studies of eating behavior cited above demonstrate that it becomes markedly fixed.
FORMING A HABIT
How does this habit develop?
If you have ever taken an introductory psychology course, you’ve undoubtedly heard of operant (or instrumental) conditioning. (Remember Skinner’s box?) Very simply, it is a form of learning whereby behaviour is shaped by its consequences. If a rat realizes that pressing a lever leads to a reward, such as food, it will learn to keep pressing the lever. If, on the other hand, pressing the lever leads to a punishment, such as shock, the rat learns to avoid pressing the lever. When it comes to this type of learning, we are not too different from rats.
Importantly, after the behaviour is acquired because it continues to lead to reward, there comes a point when the behaviour becomes almost insensitive to the reward. That is, the behavior may continue even after it no longer leads to reward. This is the basis of habit formation.
How does this relate to the development and persistence of anorexia nervosa?
In the model presented here, which is based on these principles of learning, it is hypothesized that the dieting behaviors of individuals with anorexia nervosa begin as goal-directed actions that lead to weight loss, which is highly rewarding […] Over time, the dieting behaviors are engaged in persistently and repeatedly and thereby become overtrained and habitual […] Once they have become established as habitual, the behaviors are highly resistant to change and are a critical element in the persistence of the disorder.
REINFORCING THE DIETING HABIT
When a rat presses a lever and receives food, the reward is clear. But what’s the reward in restricting food intake? What’s the reward in, essentially, starving? Walsh outlines two main reinforcers that contribute to forming the restriction habit and maintaining the anorexic state:
- Positive reinforcement: Culturally maintained association of weight loss with self-control, achievement and attractiveness.
- Negative reinforcement: Restricting food intake as a way to regulate or cope with negative emotional states.
Overtime, the very act of restricting food intake becomes reinforcing (acting as a secondary or conditioned reinforcer) due to its association with weight loss and/or the removal (or numbing) of a negative emotional state.
REWARDS DURING ADOLESCENCE
Many individuals begin to diet (or at least consciously modulate their food intake) during adolescence. A time of great physical and psychological changes. A time, also, when a lot of psychiatric disorders emerge.
Adolescence is a rough time for many (puberty [and everything that comes with it!], gaining independence, having to decide what to do with your life — at least in the immediate future). It is also a time when individuals are most sensitive to reward (more than children or adults!). Can this increased sensitivity to rewarding stimuli at least partly explain why adolescents are prone to developing substance abuse issues, and, perhaps, similarly explain the development of eating disorders such as anorexia and bulimia nervosa?
WHEN RESTRICTING BECOMES INGRAINED
In addition to the positive and negative reinforcements, as well as the increased sensitivity to reward, Walsh outlines several other factors that may lead to restricting becoming ingrained:
- Persistent and repeated dieting –>overtrained and highly practiced –> entrenched behaviour.
- Intermittent rewards = stronger reinforcer. I’m not sure I buy the argument that “daily weight loss is not inevitable, and the receipt of social accolades for becoming thinner occurs only occasionally.” While this is certainly the case for some, I would argue that for others, the positive effects of feeling like you’ve accomplished something by eating less (achieved a goal) and the effects of numbing emotions are much more reinforcing.
- Onset of anorexia nervosa typically coincides with stress and we learn better when we are stressed. So, behaviours that are acquired during a time of stress are more likely to become habits than when they are learned at other times.
- Weight loss itself leading to compulsive, obsessive, and rigid patterns of thought and behaviour. The most cited example of this is the Minnesota starvation study, where healthy subjects developed symptoms of obsessionality much like anorexia nervosa patients following a period of starvation.
RELATIONSHIP TO OTHER MODELS
The model presented here is quite similar to some previous models proposed by others, particularly the model proposed by Michael Strober, who hypothesized that:
Individuals who develop anorexia nervosa have an underlying propensity to anxiety and to fear-learning and a greater resistance to its extinction than unaffected individuals. Like the model presented here, Strober’s model is based on relatively recent advances in our understanding of how behavior is acquired and is shaped by internal and external stimuli. It suggests that negative emotion, specifically anxiety, about weight gain leads to enduring patterns of dieting.
Walsh emphasizes that the model presented in the paper does not challenge or contradict previous models — instead, it expands on them by proposing specific mechanisms by which dieting becomes rewarding and ultimately habitual.
WHAT ARE THE IMPLICATIONS OF THIS MODEL?
There are a few implications of this model, but I’ll just mention two that I think are most important:
One, we need to treat eating disorders early — before the behaviour becomes entrenched. (Yeah, I’m looking at you insurance companies and stubborn doctors. Get with it.) Although we knew this even without this model, the model (if true) certainly further emphasizes the importance of early intervention. The data is clear: early onset and short illness duration are some of the strongest predictors of a complete recovery. (But, my fellow adult readers, please don’t let this decrease your motivation or leave you feeling hopeless. These are statistical associations — don’t let them dictate your efforts.)
Two, effective treatments probably need to really tackle the ingrained restricting behaviours in order for them to be successful in the long-term. That doesn’t tackling restriction is sufficient — it isn’t. But it is, obviously, necessary. I think when restricting is viewed as a strongly entrenched and powerful habit, it helps clinicians, patients, and families understand why “eating a sandwich” is so freaking hard, and why “eating a sandwich” has to continue for a long time before it becomes a habit that overrides the dieting habits of anorexia nervosa.
As of now, this is just a model, and although separate elements are well-established, the model as it applies to anorexia nervosa isn’t. So, next is the fun part (well, for a research scientist): testing the model. One interesting question that can be studies is the ability of anorexia nervosa patients to develop and extinguish habits when (1) underweight, (2) partially recovered, and (3) fully recovered. That would be an interesting study — though, I wonder, whether the findings would be generalizable to dieting behaviour.
Walsh emphasizes that this model addresses only one aspect of anorexia nervosa. It does not directly address vulnerability, the onset of binge eating, excessive exercise, and so on. But, in my opinion, it is not hard to integrate this model into other models that do address those things.
I’ll conclude with a great summary of the model provided by Walsh near the end of the paper:
The developmental and psychosocial context in which anorexia nervosa develops sets the stage for weight loss and, over time, the characteristic dieting behaviors themselves to become intensely rewarding. Several additional factors lead to dieting behavior becoming a well-established habit and very resistant to change. This formulation thereby provides a possible insight into the impressive persistence of anorexia nervosa once it has developed. However, other factors, both innate and acquired, undoubtedly also contribute to its chronicity, including biological, psychological, and environmental influences that reduce emotional and behavioral flexibility.
So, readers, what do you think?
Walsh, B.T. (2013). The enigmatic persistence of anorexia nervosa. The American Journal of Psychiatry, 170 (5), 477-84 PMID: 23429750