Authors: Kathryn Hansen
Although it may seem difficult to think of the similarities between bulimia and an incorrect tennis serve, the two habits form in much the same way. Each time I binged and purged, I made the neural connections driving my behavior stronger and more efficient. Each binge-purge cycle was like practice that eventually made my problem permanent. During every binge, and during every purge, the behaviors and all the thoughts and feelings that went along with those behaviors got programmed into the very structure of my brain; and once that happened, my habit took over. It automatically produced urges to binge no matter how much I wanted to change.
My habit-driven bulimia was what I'll call a "binge-created brain-wiring problem." I'll use the term frequently through the remainder of the book, so I will define it here for reference:
A
binge-created brain-wiring problem
is a harmful brain condition that develops due to the repeated destructive action of binge eating. It is the physical expression of the bulimic habit in the brain.
By binge eating enough times due to my survival instincts, my bulimia became part of the very physical structure of my brain, which ensured that my body and brain continued to expect and demand the binges. I had wired neurons together in a way that was harmful to me. My brain was never faulty or diseased, but I had created unwanted, but fine-tuned and strong neural connections that produced destructive urges and compelled me to perform unwanted behaviors for many years.
The development of my habit of bulimia looked something like this:
Dieting —> Survival Instincts —> Urges to Binge —> Binge —> Purge —> More Urges to Binge —> Repeated Survival-Instinct-Driven Bingeing (and Purging to Compensate) —> Habit Formation in the Brain —> Brain Automatically Produces Urges to Maintain the Binge Eating Habit
I cannot pinpoint exactly when survival instincts stopped driving my behavior and habit started driving it, but I'm sure it was a gradual process. By the time my survival instincts died down, the habit of bingeing was already firmly established, which made the gradual change mostly imperceptible to me. However, looking back, I can identify one difference in survival-instinct-driven binges and habit-driven binges. In habit-driven binges, I seemed to eat a little less frantically than I did during those first several months of binge eating when I was underweight. It seems my body knew—at some level—that I didn't truly need so much food anymore, but I still felt driven toward it. Despite this minor difference, habit-driven binges still made me feel out of control and the urges still felt like a terrible intrusion in my life.
WHERE AND HOW DID THE HABIT FUNCTION IN MY BRAIN?
If I had access to neuroimaging devices, I may be able to give a firm answer to this question. But no one scanned my brain at the time, so I can't be sure where and how my habit functioned. In other words, I can't pinpoint exactly where my binge-created brain-wiring problem took hold, just as I cannot pinpoint exactly when it took hold. The specific neural pathways that drive eating disorders haven't been identified, but more researchers are studying the neuroscience of eating disorders in order to better understand them in terms of the brain.
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It's likely that an eating disorder "involves abnormal activity distributed across brain systems,"
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but currently, little is known about these brain abnormalities.
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Although we can't precisely locate where the habit of bulimia takes hold in the brain, there are still a few possibilities to present, based on what is currently known in neuroscience.
I received clues to where my habit existed during my experience on Topamax (topiramate), which provided a temporary reprieve from my urges to binge. As I talked about in Chapter 7, Topamax is an anti-epileptic drug that is sometimes used to treat bulimia and binge eating. Topamax has effects on weight and appetite and "on neural systems important in regulating eating and weight control."
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The drug is associated with decreased appetite and weight loss, at least in the short term.
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Topamax seemed to nearly shut down my binge-created brain-wiring problem for a short time; so knowing how Topamax works gives me an idea of the nature of my habit. The exact brain mechanism through which Topamax exerts its effects in bulimics isn't known at present,
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but there are three possible mechanisms that apply to my experience, all of which result from neuroplastic changes in the brain.
A Habit of Excess
Some researchers hypothesize that Topamax reduces binge eating by simply decreasing appetite and enhancing fullness
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through several possible neural pathways. One possibility is that Topamax reduces neuropeptide Y (NPY) activity in the hypothalamus.
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NPY is a powerful feeding stimulant in the nervous system, and researchers have found elevated levels of NPY in bulimics.
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Furthermore, Topamax suppresses the glutamate system—a system that stimulates appetite.
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It could be that by binge eating many times due to survival instincts, I conditioned a very strong appetite, mediated by NPY, the glutamate system, or another mechanism in my brain and nervous system. I simply made my body and brain physically dependent on excessive amounts of food. In this way, my binge-created brain-wiring problem resulted from strengthening neural pathways and affecting neurochemicals that supported this extreme appetite; and it is possible that Topamax temporarily tamed those pathways and neurochemicals.
A Habit of Pleasure
Another theorized mechanism through which Topamax works is by reducing the reward of binge eating.
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Binge eating is certainly motivated by the pleasurable properties of food, and like I said in the last chapter, highly palatable food is necessary for binge eating to occur. Topamax has been shown to reduce nicotine-induced increases of the pleasurable brain chemical dopamine in the brain of rats,
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and it could have a similar affect in reducing the pleasurable brain chemicals associated with binge eating, as well as other addictions.
As I've mentioned, the opioids—one class of pleasurable brain chemicals—are a possible culprit in the rewarding nature of binge eating.
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A history of caloric restriction can alter opioid-receptor function and make one more susceptible to binge eating.
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Then the rewarding properties of highly palatable food activate the altered opioid system, and binge eating can result.
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Further, eating foods high in carbohydrates increases serotonin, a neurotransmitter that produces feelings of relaxation and calmness, giving binge eating a soothing, mood-altering quality.
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Yet another feel-good brain chemical—dopamine—could be involved as well.
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Whether it's through opioids, dopamine, serotonin, or a combination of the three, binge eating activates a pleasure process in the brain and is therefore very rewarding to bulimics. Indeed, it's been shown that people with a high reward sensitivity—a biologically based personality trait that makes one more pleasure-seeking—have a higher risk of addiction and overeating.
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Maybe I found more pleasure in binge eating due to this trait; and by dieting and then binge eating over and over, I further heightened my reward sensitivity. In this way, I made my body and brain dependent on the temporary pleasurable effects of binges. My binge-created brain-wiring problem, then, was the sum of all my bungled but strong pleasure-seeking neural pathways. Topamax could have reduced the incentive value of binge eating by regulating those overactive pathways.
A Habit of Impulsivity
It's possible that my binge-created-brain-wiring problem was a habit of impulsivity. It's been shown that bulimics and those with BED are more impulsive, sometimes pathologically so, and Topamax has been shown to decrease other impulsive behaviors besides binge eating.
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By succumbing to my survival drives over and over, I may have weakened the higher, rational parts of my brain responsible for voluntary action (at least when it came to binge eating) and strengthened those neural pathways responsible for the automatic behavior.
I could have been generally more impulsive even before my eating disorder began, which could explain why I had so much trouble resisting survival drives. Neuroscience research has shown that women with bulimia are less adept at self-control, even in tasks unrelated to eating.
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Women in one particular study did not engage circuits in the prefrontal cortex as effectively in a mental task as those without bulimia.
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Moreover, adolescents who have attention-deficit/hyperactivity disorder (ADHD)—a disorder characterized by impulsivity—are at greater risk for developing bulimia.
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It could be that I was already impulsive to begin with, and my repeated binge eating strengthened the neural pathways that supported my impulsive eating and weakened the neural pathways that could have allowed me to resist the urges. Thus my binge-created brain-wiring problem was the result of a weak will—not in a metaphorical sense, but a real neurologically based weakening of the parts of the brain that control voluntary actions. This does
not
mean I wasn't capable of resisting—I was simply out of practice and using the wrong tactics; but by succumbing over and over to my urges to binge, I only made it easier to keep giving in.
As I've said, I believe all three types of habits probably worked together to keep me binge eating. The habits of excess and pleasure fueled my urges, and the habit of impulsivity made me feel less capable of saying no, even though I certainly retained that ability. I always knew that I somehow had a choice of whether to binge or not, but I was usually not successful at exercising that choice. In the next chapter, I'll explain why I followed my urges to binge over and over again. But first, I need to address the fact that some people can and do develop a binge eating habit without ever dieting.
NO DIETING REQUIRED?
Although my experience with dieting and weight loss preceding the onset of binge eating mirrors the vast majority of bulimia cases, the disorder can occur without an initial diet. Furthermore, in cases of BED, binge eating frequently occurs without any history of dieting. One study found that 55 percent of those with BED reported binge eating prior to going on their first diet, while 45 percent reported that dieting occurred first.
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Without dieting and survival instincts, how do we then explain the onset of binge eating in these cases?
I believe any of the habits I discussed above could develop without dieting as a catalyst. Remember, I developed a habit of pleasure, a habit of excess, or a habit of impulsivity by eating large amounts of food repeatedly. If anyone ate large amounts of food repeatedly—for whatever reason—they could theoretically develop the habit of binge eating; and if they chose to purge afterward, they could develop the habit of bulimia.
There is evidence from animal research that overconsuming foods high in fat and sugar can lead to changes in the opioid receptors in areas of the brain that control food intake.
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Regardless of how the binge eating begins, binge eating on these highly palatable foods can maintain binge eating by enhancing the opioids
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and creating a habit of excess and pleasure.
Those who binge without ever dieting may have been overeaters and binge eaters from childhood, because of learning or because of a genetically strong appetite and attraction to highly palatable food and rewarding experiences. In a person who has had poor eating habits for a lifetime and overindulged in sweet or fattening foods, the body becomes accustomed to those substances. Eventually, the person may need more and more of the highly palatable foods to experience the same pleasure or the same "high."
There is growing evidence that people can become "addicted" to highly palatable foods like refined carbohydrates and saturated fats—or at least people can exhibit behaviors that show similarities to addiction. Indeed, there are many parallels between food craving and drug craving—in the neurochemistry, neuroanatomy, and learning involved.
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There is evidence of tolerance and withdrawal—two of the defining characteristics of addiction—in animal studies.
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Although the addicting nature of highly palatable foods does not excuse binge eating, it does provide an explanation for urges to binge in those who do not diet.