Neurobiological & Psychological Factors that Influence Bulimia: An Interview with Dr. Carol Peterson

It was my absolute honor to interview Dr. Carol Peterson about the neurobiological and psychological factors that influence and maintain bulimia nervosa. Peterson, PhD, LP is a Professor in the Department of Psychiatry and Behavioral Sciences at the University of Minnesota Medical School. At the Minnesota Center for Eating Disorders Research, she is the Program Director of a multisite T32 Midwest Regional Postdoctoral Training Program in Eating Disorder Research and a clinician in the Interventional Psychiatry Program. Dr. Peterson has authored over 200 articles and book chapters and has received several federally-funded grants. She is also a Fellow of the Academy for Eating Disorders and on the Editorial Board of the International Journal of Eating Disorders.

I think one of the most exciting areas of research in eating disorders today is discovering and targeting the neurobiological factors that influence and maintain eating disorders. We are all exposed to similar societal messaging regarding “ideal” body size, diets, and extreme beauty standards, yet only a small percentage of individuals will develop bulimia. Will you please review significant unique brain findings in individuals with bulimia and the basic technology being used to discover the findings?

It's a really important question and I absolutely agree. First, we know that many environmental factors can put people at risk of eating disorders and then potentially precipitate the onset of eating disorders. In spite of these risk factors, only a small percentage of people develop bulimia nervosa, approximately 2% of the population. We are trying to determine who develops eating disorders, how to identify these individuals, and the most effective ways of targeting maintenance factors that keep people stuck in eating disorders in evidence-based treatments. State-of-the-art research uses neuroimaging, especially fMRI, to understand how the brains of individuals with eating disorders respond to different stimuli. For a while now, we've known that certain brain regions are important in eating disorders. For example, the insula impacts self-awareness, interoception, and integrative thinking.  Now, the field has evolved to focus on understanding specific neural circuitry. For example, we are trying to understand reward circuitry in the brains of people of bulimia nervosa, including how they anticipate and experience things that are rewarding, and how this works in the context of decision making. Using fMRI allows us to see, in real-time,  how brains respond to specific tasks. We're currently doing a study to investigate anticipatory reward and links with emotion in adults with bulimia. While participants in this study are being scanned using fMRI, we will use a mood induction to elicit different mood states and then have them look at and rate different foods (we also have them rate shopping items from Target as a comparison).  This research allows us to examine the neurobiology of anticipatory reward responses and how they differ between people with bulimia and people without bulimia. In this study, we are also using what's called ecological momentary assessment, where we have people carry around their cell phones and we'll signal them multiple times a day to ask them to use their cell phones to report what they are feeling, what they are eating, and what they are planning. We will then be able to determine how neurobiological patterns that we observe in neuroimaging are linked with eating disorder behaviors that we observe in the environment. 

—We hope that our findings will help us develop more effective treatments. For example, we know that a number of people with bulimia will actually plan out their binges ahead of time. They'll be thinking about binge eating episodes sometimes hours, sometimes days before they occur. Typically, as therapists, especially for cognitive-behavioral therapy and dialectical therapy,  we will focus on the immediate factors leading up to the onset of a binge episode.. 

Our research is helping us understand if we need to start targeting our treatments much earlier in the binge eating sequence, to the time when someone with bulimia starts to think about and plan a binge eating episode. Researchers at UC San Diego as well as at Mt. Sinai in New York have found  that individuals with eating disorders often have similar responses to those of people without eating disorders when they eat food, but a different response in anticipating eating food. —We also understand that factors like depression can impact neurobiological reward systems. Our research team is very interested in momentary factors like mood, stress, and craving, and how these experiences impact binge eating and purging. We have learned that behaviors associated with bulimia nervosa can often be very reinforcing, and we are trying to understand how these decision-making and learning processes work in order to target them in treatment.

Another approach to research in eating disorders that is really exciting right now is what's called computational psychiatry, which allows us to examine how people make decisions, how this decision-making process is linked with neural circuits, and how people make predictions about the future. Learning about these patterns of decision making is especially important in understanding how expectancies work (for example, how someone with bulimia predicts they will feel after bingeing and purging) as well as the role of habit in maintaining eating disorders.

How does genetics influence the neurobiology in those with bulimia nervosa? 

When I started in the field in the 1980s, we thought that bulimia was mainly a sociocultural disorder. We understood that experiences like trauma could increase someone’s risk of developing an eating disorder, but we did not understand the importance of genetic influences. The genetic data are really clear from twin studies and other types of research, suggesting that about fifty percent of the likelihood of developing bulimia is related to genetics. However, we're not exactly sure what is inherited.  Dr. Cynthia Bulik’s research team has helped us understand the importance of metabolic factors in the genetic risk of anorexia nervosa, but we are less clear about the genetics of bulimia other than it being very important. Research by Kelly Klump’s lab has also helped us understand the influence of hormones during puberty on genetic factors. However, there is much more to be understood about the genetics of bulimia nervosa and the heritability of metabolic processes, neurobiology, the gut microbiome, hunger and satiety mechanisms, and personality, for example, We are also interested in understanding the potential impact of what’s called epigenetics, meaning that certain types of genes can be switched on through environmental influences (potentially including dietary restriction). 

Do you believe the same temperament traits that predispose/maintain an individual to bulimia can also help them to achieve full recovery? 

I'm inclined to say yes for some people. There's really beautiful work being conducted by Laura Hill and her colleagues at UC San Diego looking at temperament-based treatment for anorexia nervosa. There's less clarity around how this applies to other types of eating disorders including bulimia. But I think we are understanding that individuals with eating disorders including bulimia nervosa have high levels of sensory processing sensitivity, which means they may be very good at detecting errors in their environment and, potentially, within themselves (which may put them at risk of the negative effects of perfectionism). Sensory processing sensitivity and error detection are probably related to genetics and neurobiology and may be impacted by certain life experiences. The data suggest that there's a percentage of us who are just very sensitive to external stimuli, internal experiences, and sensory processing.

These types of temperament and sensory processing tendencies can be great resources in the context of recovery For example, if you're often stress-reactive and self-aware of what's happening among others around you,  these vulnerabilities can be used as strengths in deepening self-awareness, developing resilience, and increasing clarityIt is extremely important for us as clinicians and also for anyone recovering from an eating disorder to bring that curiosity about oneself to recovery--what are your natural traits? How might they make you vulnerable? We know that people with sensory processing sensitivity may be very sensitive to what we call social threat. So, if someone's rude to them at Costco, that can have a real impact. But sensitivity to social threat may also help someone in recovery seek out positive interpersonal experiences.  Interpersonal sensitivity can help someone in recovery if they can get support from people in a way that's deeply validating and makes them feel a sense of belonging. I often say to people who are prone to anxiety and fear that it’s an extremely positive trait from an evolutionary standpoint. Nancy Zucker at Duke has these amazing videos that are available on YouTube to help people with ARFID (Avoidant Restrictive Food Intake Disorder) understand that food sensitivity to disgust, taste, and texture are probably things that served us well in evolution. However, we can learn from practice that things that seem threatening to us—a food’s texture, for instance, or public speaking—are not dangerous. The more we practice them, the less threatening they are experienced.  For me, understanding our own resilience is being able to say, "Okay. My primitive brain is telling me that this is dangerous, but it's really safe."  Although these types of sensitivity can make us more vulnerable to eating disorders, these aspects of our temperament can also heighten our resilience, fortitude, and strength in recovery. 

I think that's where the field is taking us.  I wrote this paper with one of my heroes in the field, Leslie Sim, about sensitivity and eating disorders, and we're just in the process of doing a follow-up paper. Leslie’s view is that we really shouldn't be talking about vulnerability without always talking about strengths. Because with every vulnerability, there's always a strength. Susan Cain wrote about the strengths associated with introversion and Elaine Aaron was the first to write about the powers of sensitivity.  These strengths have an enormous impact.

We know that perfectionism is something that not everyone with eating disorders experiences, but many do. One of my mentors always says, "There's nothing wrong with having high self-standards, it's just a question of how you treat yourself when you don't meet those self-standards." And I really like this idea of practicing a flexible response to the outcome, how building in that cognitive flexibility and self-compassion can be so positively impactful in the context of recovery. 

Why is it so important to learn if there is a unique genetic or brain difference in those with bulimia in terms of helping them to reach full recovery? Specifically, how are new neuroscience-informed interventions different from previous standards of care?

The more advanced our understanding of the neuroscience of bulimia, eating disorders, psychopathology, and psychiatric conditions,  the more successful we will be at implementing what's called precision medicine and personalized care. Because as much as we want to understand trends of what happens for people with bulimia, we always know that there's heterogeneity and individual differences. In our treatments, we want to be able to target what works for a specific person. Where our neuroscience models and a lot of our computational and quantitative models are taking us, is to be able to have someone come into treatment and potentially have them do some sort of neuroimaging to understand their brain patterns and how best to focus treatment.  Should treatment target reward or threat?  Should treatment help someone process information in different ways?  We know that our existing treatments are helpful for many people, but not everyone, and we are hoping that we can improve our treatments by better impacting these complex maintenance mechanisms in tailored, individualized treatment..  I also hope that the more we understand the impact of genetics, the better we will understand the role of the environment and how that increases eating disorder risk and maintenance. We used to see trauma as a circumscribed type of experience that people might experience in combat. We're understanding now that certain attachment experiences and social experiences like being bullied, are extremely impactful including the impact on their brain. And in the same way that our brains can react negatively to things that occur, our brains are very plastic and malleable so we can have positive influences on our brain circuitry as well. So to me, neuroscience can help us understand the role of environment,  including sociocultural factors related to body image, body ideals, and gender roles.  We are understanding the tremendous impact weight stigma as a negative health factor, and this negative societal factor may be impacting people of all BMI levels. Advancing neuroscience will also help us understand how and which individuals are most influenced by these societal factors, as well as how important it is for us to change weight stigma due to its negative effects.

Neuroscience can also help us determine the complexity of mechanisms that contribute to the causes and maintenance factors of bulimia, as well as how they should be targeted for each individual. Interventions can include neuromodulation where you're directly targeting neural circuits, as well as traditional treatments,  cognitive-behavioral, mindfulness, and emotion-focused interventions. Neurosciences will also help us measure how these treatments work, and for whom they work best, in facilitating long term recovery from eating disorders.

Additional research on the gut microbiome is also revealing how it influences the regulation of eating behaviors and metabolism. How can these findings work with your research on psychological and neurobiological factors that maintain bulimia?

To me, the gut microbiome is like the new frontier.  As you highlight in your question, it has a huge influence on multiple factors involved in bulimia including psychiatric conditions like depression, body mass index, and metabolic factors. Emerging data suggests that the gut microbiome is also involved with inflammatory processes.

It's complicated because there are all kinds of things that the gut microbiome seems to impact, and all kinds of factors that influence the gut microbiome. But one thing that looks to be clear is for people with eating disorders, there's a lower level of diversity within the gut microbiome. How we increase diversity in the gut microbiome is unclear. There's interest in probiotics and we also know that as people recover from bulimia, you’ll see an increase in diversity that may be the result of changes in eating patterns.  There is a lot of complexity with the gut microbiome impacting so many processes, and then there are other factors that we know are directly impacting the gut microbiome--what we're eating, how we're eating, and our living environment.  I think that the gut microbiome may be critical piece of the puzzle both as an eating disorder biological marker, but potentially as a way of trying to help people in their recovery.

It seems like the old thinking was Nature vs Nurture but modern research is showing more of a complex collaboration, even if we don’t know exactly “who started it.” Is it ever okay in research to say we don’t know who started it but now that we have the contributors we can (potentially) stop it?

There is still tremendous work in trying to unravel the complexities of the causes of eating disorders, which as you say are highly, highly complex.  I agree that it's not nature versus nurture. It's both interacting in very complex ways.  It’s especially complicated in eating disorders, because there are causal factors and precipitating factors, and then a whole set of maintenance factors that may overlap with causal factors or may be independent of them.  In our research, we are trying to understand the complexity of maintenance factors so that regardless of someone’s developmental history, genetics,  and precipitating factors, what we really want to understand is what's someone stuck or trapped in their bulimia. How do we disentangle the complexity of biology, psychology, and environmental factors using individualized approaches to help people in their recovery?

Through research coming out of COVID, we're seeing the negative impact of social isolation and the reverse--the degree to which a sense of belonging and very strong interpersonal support seems to be a key factor in aging and in health across the lifespan. To me, it's a lot more interesting to try to understand the complexity of how these work together, both in the causal factors and in the maintenance factors, rather than trying to isolate one thing versus the other. And yet we do need to understand the different components and how they all intertwine.  The process can be highly dynamic too. For example, what may be contributing to the maintenance of someone's bulimia may change over time. There's a lot of interest right now in the neuroscience of habit and it may be that when people's eating disorders start,  positive reinforcement is important, then people find that they're kind of stuck in their bulimia because if they don't engage in these behaviors, they feel worse. Some of the neuroscience data from researchers at Columbia including Joanna Steinglass suggest that over time,  eating disorders may be sustained by habit. To determine how to best help people with bulimia recover, we will want to continue to understand  not only the complexities of maintenance factors but how they change over time, and how we can most effectively target them in treatment. 

Author: Merrit Elizabeth, CCI Certified Eating Disorder Recovery Coach

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