Anorexia nervosa doesn’t have a single cause. It develops from a collision of genetic vulnerability, brain biology, metabolic traits, hormonal shifts, and environmental pressures. Twin studies estimate that genetics account for roughly 50 to 80 percent of the risk, placing it among the most heritable of all psychiatric conditions. But genes alone don’t determine who develops it. The condition emerges when biological predisposition meets the right combination of psychological and social triggers.
Genetics Play a Larger Role Than Most People Expect
Family and twin studies consistently show that anorexia runs in families, and not simply because families share eating habits. The concordance rate for identical twins is about 44 percent, compared to just 12.5 percent for fraternal twins. That gap points squarely at DNA. A comprehensive review of all published family and twin studies estimated heritability at around 71 to 72 percent, meaning the majority of variation in risk comes from genetic factors rather than environment alone.
A landmark genome-wide association study published in Nature Genetics identified eight specific genetic risk locations and revealed something surprising: anorexia nervosa has the strongest metabolic and body-composition genetic components of any psychiatric disorder ever studied. The same genes that influence anorexia also influence fasting insulin levels, body fat percentage, BMI, and cholesterol. This means anorexia isn’t purely a psychological illness. It has deep biological roots in how the body processes and stores energy.
It’s a Metabolic Disorder, Not Just a Mental One
That genetic overlap with metabolism is one of the most important recent shifts in how researchers understand anorexia. People who develop it tend to carry genetic variants associated with lower fasting insulin, lower body fat, lower leptin (the hormone that signals fullness), and higher HDL cholesterol. These aren’t consequences of starvation. They’re present in the genetic code before the illness begins.
This reframing matters because it helps explain why recovery is so difficult. Even after weight restoration, the body’s metabolic programming may pull toward lower weight. Researchers now describe anorexia as a “metabo-psychiatric” disorder, one that sits at the intersection of mental health and metabolic biology. The psychological drive to restrict food and the body’s metabolic tendencies reinforce each other.
How the Brain Responds to Hunger Differently
In most people, hunger makes food more rewarding. The brain detects an energy deficit, activates reward circuits, and creates a strong motivation to eat. In people with anorexia, this system doesn’t work the same way. Research from UC San Diego found that hunger failed to activate the food reward circuit in people with a history of anorexia, even after they had recovered and restored their weight. Their brains could recognize the hunger signal but couldn’t convert it into the motivation to actually eat.
Specifically, the brain region involved in initiating eating behavior (the ventral caudal putamen) showed abnormal responses to hunger in people who had recovered from anorexia compared to healthy controls. When both groups were full, their brain responses to food looked similar. But when hungry, the anorexia group’s brains didn’t ramp up the reward signal the way they should have. On top of that, anxiety actively suppressed this food reward signal, meaning stress and worry made it even harder for the brain to motivate eating.
Dopamine Creates a Self-Reinforcing Cycle
The brain’s dopamine system, which governs motivation, reward, and habit formation, plays a central role in how anorexia develops and becomes entrenched. Researchers have proposed a two-stage model. In the first stage, caloric restriction (especially combined with exercise) triggers an escalating spiral of increasing dopamine. This surge in dopamine reinforces the weight-loss behaviors, making restriction feel rewarding and creating strong habits around food avoidance and excessive activity.
In the second stage, chronic starvation reverses this pattern. Dopamine levels drop or become impaired, which creates behavioral inflexibility. By this point, the restrictive habits are deeply established but the person has lost the neurological flexibility to change them. The illness essentially rewires the brain’s reward system twice: first to lock in the behaviors, then to make those behaviors resistant to change. This is one reason anorexia has the highest mortality rate of any psychiatric disorder and why early intervention matters so much.
Hormonal Changes That Maintain the Illness
Once someone begins restricting food intake, the body’s hormonal landscape shifts dramatically. Leptin, the hormone that signals energy stores and fullness, drops to very low levels. This makes sense biologically since leptin is produced by fat cells, and those are shrinking. Low leptin then cascades into disruptions of growth hormone, cortisol, estrogen, and thyroid hormones.
What’s more puzzling is ghrelin, the “hunger hormone” that normally drives food-seeking behavior. In people with anorexia, ghrelin levels are elevated, sometimes significantly. Their bodies are screaming for food at a hormonal level, yet they continue to restrict. This paradox likely reflects the broken reward circuitry described above: the hunger signal arrives, but the brain can’t translate it into motivation to eat. These hormonal changes appear to be consequences of starvation rather than original causes, but they create a feedback loop that makes the illness self-perpetuating.
The Gut Plays a Role Too
Starvation profoundly alters the community of bacteria living in the gut, and those bacteria communicate directly with the brain. People with anorexia show significant changes in their gut microbiome, which is relevant because these microbes influence weight regulation, immune function, inflammation, and even mood. Specific bacterial populations shift in ways that affect hunger and fullness hormones. Higher levels of certain bacteria (like Bifidobacterium and Lactobacillus) are associated with increased leptin, while others (like Bacteroides and Prevotella) show inverse relationships.
Gut bacteria also influence stress hormones. Administering Lactobacillus and Bifidobacteria has been shown to decrease circulating stress hormones in both humans and animals. Since anxiety disorders co-occur with anorexia nearly half the time, and since stress directly impairs the brain’s food reward signal, the gut microbiome may be one more biological system that keeps the illness locked in place once it starts.
Anxiety and Depression Often Come First
Anorexia rarely exists in isolation. About 56 percent of people with anorexia meet criteria for at least one other psychiatric disorder, and nearly half (47.9 percent) have an anxiety disorder. Depression affects 42.1 percent over their lifetime, obsessive-compulsive disorder affects 27.1 percent, and social phobia affects 32.2 percent. In many cases, the anxiety or OCD predates the eating disorder, suggesting these conditions create psychological soil in which anorexia can take root.
Perfectionism, rigidity, and a need for control are personality traits that frequently appear before anorexia develops. These traits overlap heavily with OCD and anxiety. When someone with this psychological profile encounters stress, puberty, or cultural pressure around body size, restrictive eating can become a coping mechanism. The initial restriction then activates the dopamine and reward changes that transform a coping behavior into a full disorder.
Social and Cultural Pressures
Environmental factors don’t cause anorexia on their own, but they can trigger it in someone who is biologically vulnerable. Social media use is one increasingly studied risk factor. Research shows that increased use of image-focused platforms like Instagram and Snapchat is associated with significantly higher scores on eating disorder questionnaires among adolescent girls. In one study, 96 percent of teenagers who visited pro-eating disorder websites reported learning new weight loss or purging techniques there.
The median age of onset for anorexia is 18, a period when social comparison, identity formation, and body image concerns are all intensifying. Cultural idealization of thinness provides a framework that can shape how genetic and neurobiological vulnerabilities express themselves. Someone with the same genetic risk profile born into a culture without these pressures might never develop the disorder. But in environments saturated with appearance-focused messaging, vulnerable individuals are more likely to begin the caloric restriction that starts the biological cascade.
Why It Affects More Women, but Not Only Women
Lifetime prevalence of anorexia is about 0.9 percent in women and 0.3 percent in men. The three-to-one ratio likely reflects a combination of biological differences (hormonal cycles, body composition, and fat distribution are all influenced by sex hormones that interact with the metabolic genetics of anorexia) and differential cultural pressure around thinness. Men with anorexia are actually more likely to seek treatment (50.2 percent) than women (29.8 percent), possibly because the illness is recognized as more unusual in men and prompts earlier concern from others. Overall, only about one-third of people with anorexia ever seek treatment specifically for their eating disorder.