Anorexia nervosa rarely starts with a single event. It typically develops from a combination of genetic vulnerability, personality traits, and environmental pressures that converge during a specific window of life, most often between ages 15 and 19. What might begin as a seemingly ordinary decision to “eat healthier” or lose a few pounds can, in the right conditions, lock into a self-reinforcing cycle that becomes increasingly difficult to break.
The Typical Age and How It Begins
Most cases of anorexia emerge during adolescence, with peak onset between ages 15 and 19. Studies in the U.S. report a median age of onset around 17 to 18, though some epidemiological research focused on adolescents finds early signs appearing between ages 11 and 13. The disorder can also develop in adults, with onset sometimes occurring into the early twenties.
The starting point often looks unremarkable. A teenager decides to cut out certain foods, starts skipping meals, or takes up a new exercise routine. In the early phase, friends and family may even compliment the weight loss. But underneath, the behavior is driven by something more rigid than a casual health goal. The person begins categorizing foods as “safe” or “dangerous,” develops strict rituals around meals, and feels mounting anxiety at the thought of eating outside those rules. The critical shift happens when restricting food intake stops being a choice and starts feeling like a compulsion.
Genetics Set the Stage
Anorexia has a strong inherited component. A large Swedish twin study of over 31,000 people estimated heritability at roughly 56%, meaning more than half the variation in risk comes from genetic factors. The remaining risk splits between a person’s unique life experiences (about 38%) and shared family environment (about 5%).
Research on families with multiple affected members has identified regions on chromosomes 1, 2, and 13 that appear linked to susceptibility. Genes in these regions affect the serotonin system, opioid receptors, and a protein called brain-derived neurotrophic factor (BDNF) that plays a role in brain development and appetite regulation. Dopamine receptor genes have also been studied in connection with anorexia. None of these genes cause the disorder on their own. Instead, they create a biological landscape where certain personality traits and brain responses are more likely to develop, and where environmental triggers are more likely to take hold.
Brain Chemistry That Reinforces Restriction
Once someone begins restricting food, their brain chemistry starts to shift in ways that can make the behavior self-sustaining. Dopamine, the chemical messenger tied to reward and motivation, becomes more reactive during periods of food restriction. When a person who is already undereating does eat, the dopamine surge can feel overwhelming or even unpleasant rather than satisfying. This creates a paradox: eating feels wrong, while not eating feels like relief.
Serotonin, which influences mood and anxiety, also changes. Low-fat diets, which are common among people developing anorexia, reduce serotonin activity in key brain areas. For someone already prone to anxiety, restricting food may initially dampen that anxious signal, creating a temporary sense of calm and control. The brain essentially learns that not eating reduces distress.
There is also evidence that the body’s own opioid system gets involved. Sustained starvation triggers the release of endorphins, the same chemicals responsible for a “runner’s high.” Animal research shows that starving subjects develop elevated levels of these natural opioids, and when given an opioid-blocking drug, they show signs resembling drug withdrawal. This suggests the body can develop a form of physiological dependence on the starvation state itself.
Personality Traits That Increase Vulnerability
Certain psychological characteristics show up consistently in people who develop anorexia, often years before the disorder appears. Perfectionism is one of the strongest predictors. People with high perfectionism scores tend to have more severe eating-related symptoms, higher rates of depression, and lower self-esteem. Research has found that perfectionism in anorexia is most closely tied to two traits: an anxious temperament and a tendency toward high cooperativeness, meaning a strong desire to please others and meet external expectations.
This combination creates a person who holds themselves to extremely high standards, feels intense anxiety about falling short, and is deeply attuned to the judgments of people around them. When that person encounters cultural messages about thinness equaling worth, or enters an environment where body shape is emphasized (competitive sports, dance, modeling), the conditions are ripe for restrictive eating to take on an outsized psychological importance.
Environmental Triggers That Set It Off
Genetics and personality create vulnerability, but something in a person’s environment usually lights the match. Dieting is the most common gateway. This often starts in the family. Studies have found that mothers’ own eating restraint and weight concerns influence their daughters’ relationship with food from as early as age five. When mothers restrict their own eating or impose tight controls on what their children eat, those children are more likely to develop disordered eating patterns later.
Stressful life events also play a significant role. Major transitions (moving, starting a new school, a family disruption), illness, physical or sexual abuse, and repeated criticism about weight or body shape have all been linked to the onset of eating disorders. Research comparing women with eating disorders to control groups found that those who developed disordered eating experienced significantly more negative life events in the year before their symptoms began. The eating disorder often starts as an attempt to regain a sense of control when the rest of life feels chaotic or threatening.
Social pressure adds another layer. Peer groups where dieting is normalized, social media environments saturated with edited body images, and activities that reward leanness all contribute. For a genetically susceptible, perfectionist teenager going through a stressful life change, these pressures can be the tipping point.
Early Warning Signs Before Diagnosis
Anorexia doesn’t arrive fully formed. There is usually a recognizable period of behavioral changes before the disorder reaches clinical severity. These signs include:
- Narrowing food choices: eating only a small set of “safe” foods, typically low in fat and calories, or adopting increasingly rigid rules about “clean” eating
- Meal avoidance: skipping meals, claiming to have already eaten, or making excuses to avoid eating with others
- Rituals around food: cutting food into tiny pieces, eating in a specific order, or chewing and spitting out food
- Social withdrawal: pulling away from friends and family, especially in situations involving food
- Body preoccupation: frequent body checking (looking in mirrors, measuring body parts, pinching skin), expressing fear of being fat despite being at a normal or low weight
- Exercise changes: a sudden increase in exercise that feels compulsive rather than enjoyable
- Dishonesty about eating: lying about how much food has been consumed
These behaviors often appear months before any significant weight loss, which means the psychological disorder is already developing while the person still looks physically healthy.
What Happens in the Body Early On
As caloric restriction continues, the body begins conserving energy in ways that become noticeable. Early physical changes include fatigue, dizziness, cold hands and feet, constipation, dry skin and hair, and difficulty concentrating. Blood pressure drops, and heart rate can slow significantly. One clinical case documented a teenager with a resting pulse of 47 beats per minute and blood pressure of 84/70, both dangerously low.
In females, menstrual cycles often become irregular or stop entirely as the body redirects energy away from reproductive function. Hair may thin on the head while fine, downy hair grows on the arms and face as the body tries to maintain warmth. These changes can happen within weeks to months of sustained restriction, depending on how severe the calorie deficit is.
The physical symptoms create a feedback loop with the psychological ones. Starvation itself impairs decision-making, increases rigidity of thought, and heightens anxiety around food. This makes it progressively harder for the person to recognize what is happening or to reverse course on their own, which is why early recognition of the behavioral warning signs matters so much.