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Simone Hoermann, Ph.D.![\"\"](\"https://www.mentalhealth.com/assets/optimized/8e1ee0ec187d4c3ff0be4ad3.jpg\")
Carlos Protzel, Psy.D.The medical profession and the general public alike have long misunderstood eating disorders. Often previously thought to be a reactive disorder driven by cultural pressures alone, increasing research indicates that biological factors play an essential role in these highly impactful diseases.
In reality, the science behind eating disorders is complex. They involve a combination of cultural, family, psychiatric, and biological factors. Understanding these influences is important for gaining a holistic view of the causes and potential treatment options for eating disorders.
Eating disorders can be incredibly harmful with potentially lethal complications. If you are worried that you or a loved one may have an eating disorder, seek support from your healthcare provider. This information is not intended to replace professional medical advice.
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Key takeaways
- Eating disorders arise from interacting biological, psychological, and environmental influences rather than cultural pressure alone.
- Genetic research and studies of hormones, metabolism, and brain signaling suggest multiple biological contributors.
- Gut microbiome research and other emerging findings may inform treatment, but many mechanisms remain under investigation.
What Are Eating Disorders?
\nThe DSM-5 is a diagnostic manual used by clinicians to classify mental health conditions. It recognizes several distinct eating disorders, including:[1]\n
- \n
- Anorexia Nervosa - features a restriction of energy intake that leads to a significantly low body weight. Anorexia nervosa is characterized by an intense fear of weight gain and a distorted body image, either with or without purging. \n
- Bulimia Nervosa - includes recurrent binge eating episodes, which are followed by recurrent compensatory behavior (such as forced vomiting or excessive exercise). \n
- Binge Eating Disorder - characterized by recurrent episodes of uncontrollable eating binges, leading to feelings of discomfort or guilt. \n
Are Eating Disorders Genetic?
\nGenetic factors form one of the key biological contributors to anorexia nervosa and other eating disorders. Although the presence of specific genes does not guarantee the emergence of an eating disorder, it can substantially increase the risk.\n
Twin Studies and Eating Disorders
\nOne of the main reasons we know that there are biological factors of eating disorders is from observing twins. Researchers commonly use twin studies to differentiate between conditions driven by genetic inheritance and those driven by a shared family environment.\n
Identical twins share 100% of their genes, whereas fraternal twins only share around 50%. As each set of twins is exposed to the same family and environmental factors, any increased risk of a condition amongst identical twins, when compared to fraternal twins, must be genetic[2].
\nGenetic predispositions have been noted for the disorders of anorexia and bulimia nervosa. Genetic factors may also underlie the presence of symptoms, such as binge eating, self-induced vomiting, and dietary restriction[2].\n
Specific Gene Variants in Eating Disorders
\nOne 2019 study identified eight distinct gene variants linked to anorexia nervosa. Of particular interest, this study suggests that anorexia nervosa shares a similar genetic basis to other mental health conditions, such as depression, anxiety, and obsessive-compulsive disorder (OCD)[3].\n
In fact, researchers have labeled anorexia nervosa as a metabolic condition and a psychiatric condition (otherwise known as a ‘metabolo-psychiatric’ condition), as it includes features of both.\n
The Role of the Brain in the Development of Eating Disorders
\nAfter making the link to genetics, it’s worth considering the effect these differences can have on brain chemistry and development. Research into the biological causes of eating disorders is still developing, and many theories are still to be fully supported.\n
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Support for eating disorders
The Role of Serotonin and Dopamine in Eating Disorders
\nSerotonin is a chemical present in the brain that primarily stimulates the reward pathways and impacts mood. Altered levels of serotonin have long been linked to impulsivity and various mood disorders. Dysregulated serotonin levels have also been correlated with eating disorders[4].\n
Serotonin has a significant effect on regulating eating behavior. However, studies are conflicting as to the exact mechanism behind why altered serotonin can lead to dysregulated eating[4].
\nA similar uncertain pattern is seen with dopamine. Dopamine also plays a central role in the reward pathways of the brain. Abnormal fluctuations in dopamine levels are thought to contribute to binge eating behaviors, potentially related to perceived rewards in association with food[5].\n
Structural Changes to the Brain in Eating Disorders
Eating-disorder behaviors and brain function can interact. In an NIH-funded study, women with eating disorders showed relationships between body mass, eating behaviors, and responses during a reward task. The findings suggest a cycle that may reinforce disordered eating, but this cross-sectional research cannot establish that a brain difference came first or caused the disorder[6][7].
Brain Plasticity and Eating Disorders
\nBrain plasticity refers to the brain's ability to change its structure and function to adapt to its experiences. Younger people have far greater brain plasticity than fully mature adults.\nIt is theorized that this increased neuroplasticity may, in part, explain why eating disorders affect such a large number of young people.
As the structure and function of the brain changes, it is more susceptible to morph in ways that continue to fuel the symptoms of an eating disorder[8].\n
Hormonal Influences on Eating Behavior
\nHormones control various functions throughout the body, including appetite and eating behaviors. Disruptions of these hormones' normal functions can lead to a variety of health conditions. One area of increasing scientific interest is the role hormones play in the development of eating disorders.\n
Leptin
\nLeptin is a hormone released by fat tissue that helps regulate appetite, metabolism, and energy regulation. Abnormalities in leptin levels have typically been associated with obesity[9].\n
However, dysregulated leptin levels may also contribute to the ongoing cycle of anorexia nervosa and other eating disorders. Deficiencies in leptin following starvation or severe energy restriction may disrupt appetite and discourage sufficient energy intake[10].\n
Ghrelin
\nGhrelin is a hormone that is similar to leptin. Ghrelin has a central role in stimulating appetite and food intake. People suffering from anorexia nervosa have been found to have consistently elevated levels of ghrelin, as the body is starving and continues to promote food consumption.
This demonstrates that, despite strong biological influences trying to regulate food consumption, eating disorders can maintain a powerful hold over individuals’ brain responses[11].\n
Cortisol
Undernutrition in anorexia nervosa can disrupt hormone regulation, including the body’s cortisol response. Clinical guidance from ACUTE describes how elevated cortisol helps maintain blood glucose during malnutrition but can also contribute to bone breakdown and affect mood and cognition. These changes form part of the medical complications that require eating-disorder treatment[12].
What Role Does the Gut Microbiome Play?
\nThe gut microbiome is a complex and fascinating area of emerging research. We are increasingly seeing the significant role gut microbes play in various physical and mental health conditions. The influences of the gut microbiome may provide an important link between the psychiatric and physical components of eating disorders.\n
Gut-brain axis
\nMany researchers have dubbed the gut microbiome as a ‘second brain.’ The development of the gut microbiome as we age is similar to brain development, being influenced by genetics, diet, and environmental exposures[13].\n
Communication between the brain's emotional and cognitive centers and the functions of the gastrointestinal tract exists as a two-way system. Disruption of this delicate balance between the brain and the gut is thought to contribute to a variety of conditions, including irritable bowel syndrome (IBS) and eating disorders[14].\n
Influence of the Gut Microbiome on Eating Disorders
\nResearch has shown that individuals who have eating disorders have a unique microbiome. These changes may occur due to nutritional deficiencies, altered digestive tract functioning, or hormonal axis imbalances[13].\nAlterations in gut microbes can worsen the symptoms of eating disorders, contributing to the common cycle of treatment resistance[13].\n
Metabolic Factors of Eating Disorders
\nMetabolism refers to the chemical reactions that occur throughout the body’s cells that turn food into energy. Eating disorders can have a significant impact on the normal function of an individual’s metabolism. However, baseline differences in metabolism may also contribute to the increased risk of developing an eating disorder.\n
Metabolic Differences
\nResting metabolic rates differ between individuals based on many factors, such as diet, physical exercise, activity level, age, sex, genetics, and others. Specifically, research increasingly shows that genetics are crucial in determining an individual’s resting metabolic rate[15].\n
The Role of Metabolic Differences in Eating Disorders
\nMetabolic abnormalities in anorexia nervosa result from the body’s response to a state of starvation. These changes can introduce significant barriers to weight gain and long-term recovery[3].\nHowever, recent research indicates that many of these metabolic changes may also have a genetic origin. This further illustrates why some people are more susceptible to developing an eating disorder than others[3].\n
What Does This Mean for the Treatment of Eating Disorders?
\nUnderstanding the biological factors of eating disorders is vital for identifying the causes and triggers of these conditions. The science behind anorexia nervosa and other related conditions is constantly progressing. Research into this field has also helped identify a variety of potential treatment approaches that aren’t limited to focusing on the psychiatric element of eating disorders alone.\n
Impact of Biological Factors on Treatment Approaches
\nA wide range of novel treatment approaches have been theorized based on the biological influences of eating disorders:\n
- \n
- Understanding the role that serotonin has in eating disorders allows for the development of more individualized treatment options. Those with serotonin dysregulation may benefit from therapies beyond just nutritional replacement, focusing also on stabilizing brain serotonin[4]. \n
- Dopamine is an important biomarker that relates to binge eating. Identification of individuals with abnormal dopamine regulation allows for the possibility of earlier identification and treatment of eating disorders[5]. \n
- Regulation of key hormones, such as leptin and ghrelin, may aid in eating disorder recovery. The medication metreleptin shows promise in its ability to support anorexia recovery[10][16]. \n
- Interventions, such as probiotics, microbiome-supplemented foods, and fecal transplants, have the potential to treat disruptions to the gut microbiome seen in eating disorders[13]. \n
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