In eating disorders, scientists have identified problems not only with the physical sensations of hunger and fullness, but also with how rewarding food is. If an animal doesn’t eat enough, it will die, so necessities like eating are generally quite pleasurable to ensure that we stay alive. This pleasure helps reinforce the behaviors, thoughts, and memories that lead to eating. Alternately, the brain usually perceives hunger as being uncomfortable to motivate us to go eat something. Research has shown us that the brain’s reward pathways are altered in individuals with eating disorders, making them more or less able to perceive and respond to pleasurable things.
Normally, when we are hungry, food is more rewarding than when we are full (Bragulat et al., 2010), as evidenced by the increased release of dopamine in the nucleus accumbens, which is known to play a role in pleasure, reward, addiction and fear (Avena, Rada, & Hoebel, 2008). Given that food restriction frequently accompanies binge eating behavior (Stice et al., 2000), the binge becomes even more rewarding in these individuals than the normal satiation of hunger. The post-binge guilt leads to further food restriction, which serves to maintain the high reward of binge eating (Carr, 2011).
Neuroimaging studies in women with bulimia revealed that their brain’s reward pathways are significantly more active than in healthy controls when they viewed pictures of food (Brooks et al., 2011). Women with the binge/purge type of anorexia also showed significantly higher reward sensitivity (Harrison et al., 2010).
Despite increased awareness and diagnosis of binge eating in males, the disorder is still significantly more common in females. Some researchers believe that female sex hormones may help increase reward sensitivity (Klump et al., 2013). Scientists are currently testing this idea.
In bulimia, purging appears to be rewarding as well. One study found a significant association between higher reward sensitivity and frequency of purging in women with bulimia (Farmer, Nash, & Field, 2001). One potential explanation for this is that purging decreases the amount of acetylcholine in the brain, high levels of which have been found to be unpleasant (Avena & Bocarsly, 2012).
This altered reward system in individuals who binge eat is evident in areas besides food. Studies have found that high school students who reported regular binge eating were much more likely to report use of drugs, alcohol, or tobacco than non-binge eaters. Those students who also engaged in compensatory behaviors like fasting or purging were most likely to use these substances (Ross & Ivis, 1999).
In anorexia, a large number of studies have instead found significantly decreased reward sensitivity, as well as an over-response to punishment (Harrison et al., 2010). Neuroimaging studies also revealed unusually high levels of cognitive processing when individuals with anorexia viewed images of food (Cowdrey et al., 2011). Because food is less rewarding and appears to be associated with fear and punishment, people with anorexia tend to place a higher emphasis on the long-term goal of weight loss and maintaining anorexic behaviors rather than food’s more immediate rewards (Kaye et al., 2013). They also tend to report high levels of ascetic behaviors (Keating et al., 2012).
These differences in reward processing across the eating disorder spectrum appear to persist after recovery (Wagner et al., 2010; Wagner et al., 2007). Because of this, some researchers believe that these results may indicate that these traits exist before disease onset and are corroborated with reports of childhood behaviors (Anderluh et al., 2003). Still, it also remains possible that these post-recovery traits are scars from the illness rather than pre-illness risk factors.
In some religious and cultural traditions, the denial of pleasure is typically seen as a good thing. Thus it may seem that individuals with anorexia have a “better” way of managing reward. This isn’t true. When you’re truly physically hungry, it’s good to focus on the immediate rewards of eating. Difficulties in shifting focus from the potential benefits of long-term goals to the more immediate benefits of feeding a starving body and pursuing recovery can keep people stuck in anorexia nervosa for years.
References:
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