Anorexia nervosa is not a choice, and it is not a diet taken too far. It is a brain and body illness in which certain people’s wiring makes eating very little feel right rather than wrong.1PubMed. A reward-centred model of anorexia nervosa: a focussed narrative review of the neurological and psychophysiological literature2PubMed. Reward processing in anorexia nervosa
Much of what doctors see in anorexia is also the body’s own survival response to starvation, and that response helps lock the illness in place. So a helpful question is often which changes come before the illness and which come from it, because many of the second kind heal with nourishment.3Clinical Nutrition Experimental. Alterations of brain structure and functions in anorexia nervosa4PubMed. The importance of the hypothalamo-pituitary-adrenal axis as a therapeutic target in anorexia nervosa
Genes Link Anorexia to Metabolism as Well as Mood
Large studies of the genes of thousands of people found eight regions of DNA linked to anorexia.5Yearbook of Paediatric Endocrinology. Genome-wide association study identifies eight risk loci and implicates metabo-psychiatric origins for anorexia nervosa The same genetic risk overlaps with other psychiatric conditions such as anxiety and depression. It also overlaps with genes that shape physical activity, blood fats and body build.6Yearbook of Paediatric Endocrinology. Genome-wide association study identifies eight risk loci and implicates metabo-psychiatric origins for anorexia nervosa That metabolic link holds even after accounting for genes that set body weight, so it is not simply a gene for being thin.7Yearbook of Paediatric Endocrinology. Genome-wide association study identifies eight risk loci and implicates metabo-psychiatric origins for anorexia nervosa Specific genes shared between anorexia and metabolism are now being identified.8PubMed Central. Exploring the Genetic Overlap Between Metabolic Traits and Anorexia Nervosa The metabolic link suggests the body’s energy regulation is part of the illness, not just thoughts about food, which is one reason doctors treat nutrition as medicine.
For a family, genetic risk means the dice are loaded, not thrown. Having a relative with anorexia raises the chance but does not make it inevitable, and dieting, puberty, stress or weight loss from another illness often pull the trigger. None of this is anyone’s fault, and it does not mean a parent caused the illness.
One theory tries to explain why the body cooperates with starvation. It holds that restricting food, not noticing starvation and restlessness were once survival tools that pushed hungry foragers to leave places without food.9PubMed. Adapted to flee famine: adding an evolutionary perspective on anorexia nervosa In people with genetic risk, losing too much weight might switch on this ancient program.10PubMed. Adapted to flee famine: adding an evolutionary perspective on anorexia nervosa This is a hypothesis, not a proven cause.
How the Brain Makes Starving Feel Rewarding
Deep in the brain, a reward hub and its chemical messenger, dopamine, help decide what feels worth doing. Some researchers think this reward system is the main brain problem behind how anorexia starts, persists and resists treatment.11PubMed. A reward-centred model of anorexia nervosa: a focussed narrative review of the neurological and psychophysiological literature People with anorexia show a stronger brain response to unexpected tastes, the opposite of what is seen in obesity.12PubMed Central. Altered Brain Reward Circuits in Eating Disorders: Chicken or Egg? That suggests their dopamine-driven reward system may be oversensitive rather than dulled.13PubMed Central. Altered Brain Reward Circuits in Eating Disorders: Chicken or Egg?
Changes in this reward hub and a nearby area that weighs effort and conflict may explain why self-starvation feels rewarding to them while it would feel punishing to others.14PubMed. Reward processing in anorexia nervosa This also challenges the old idea that people with anorexia simply can’t feel pleasure.15PubMed. Reward processing in anorexia nervosa
Food choices also run on habit. When choosing foods, people with anorexia show the same basic reward activity as others, but extra activity in the part of the brain that runs automatic habits.16PubMed Central. The Role of Habits in Anorexia Nervosa: Where We Are and Where to Go From Here? How strongly that habit area connected with a planning area predicted how much they ate the next day.17PubMed Central. The Role of Habits in Anorexia Nervosa: Where We Are and Where to Go From Here? Picking low-calorie foods may be less about strong self-control and more about an ingrained habit.18PubMed Central. Goal-directed vs. habitual instrumental behavior during reward processing in anorexia nervosa: an fMRI study At the dinner table, that can look like the same few “safe” foods eaten in the same order at the same times. Breaking habits usually takes repeated practice with new foods rather than persuasion, which is why structured, supported meals are a core part of treatment.
Anxiety, Serotonin and Misread Body Signals
Serotonin is a brain messenger involved in mood, impulse control and appetite. Serotonin differences seem to contribute to perfectionism, mood problems and other features of eating disorders.19PubMed Central. Eating disorders and the serotonin connection: state, trait and developmental effects Those differences come partly from starvation, partly from inherited traits and possibly from early stress such as childhood abuse.20PubMed Central. Eating disorders and the serotonin connection: state, trait and developmental effects Brain scans show serotonin receptor activity rises and falls with harm avoidance, a temperament mixing anxiety, caution and inflexibility.21Nature Reviews Neuroscience. New insights into symptoms and neurocircuit function of anorexia nervosa
After recovery, women who had the binge-purge type still showed altered serotonin receptors, while those with the restricting type looked like healthy women.22JAMA Psychiatry. Altered Brain Serotonin 5-HT1A Receptor Binding After Recovery From Anorexia Nervosa Measured by Positron Emission Tomography and [Carbonyl11C]WAY-100635 Some serotonin differences may be lasting traits rather than effects of low weight.
This helps explain why restriction can feel calming. Many people with anorexia describe feeling calmer when they restrict, and starvation may quiet anxiety temporarily, which rewards the restriction. Eating then brings the anxiety back, so meals start to feel threatening. This loop is one reason anxiety is treated alongside weight.
People also sense what is happening inside the body, like a full stomach or a racing heart. A brain region that reads these signals works differently in people with anorexia even after weight is restored, for both stomach and heartbeat signals.23PubMed Central. Altered Insula Activity during Visceral Interoception in Weight-Restored Patients with Anorexia Nervosa People with anorexia were also less accurate at sensing their own heartbeat, and this didn’t improve over a course of therapy.24PubMed Central. Interoceptive Processes in Anorexia Nervosa in the Time Course of Cognitive-Behavioral Therapy: A Pilot Study Signals of fullness or stress may therefore feel confusing, exaggerated or frightening. In daily life, that can mean feeling uncomfortably full after a small amount of food, or having trouble telling hunger from anxiety or nausea.
Why High Hunger Hormones Don’t Lead to Eating
Ghrelin is a hormone from the stomach that drives hunger. People with anorexia have high levels, which seems paradoxical given how little they eat.25PubMed Central. Ghrelin: Central and Peripheral Implications in Anorexia Nervosa The rise may be the body adapting to starvation.26PubMed Central. Ghrelin: Central and Peripheral Implications in Anorexia Nervosa But the hunger hormone doesn’t drop normally after meals, and giving extra doesn’t raise blood sugar as expected, suggesting the body has become resistant to it.27PubMed Central. The Role of Ghrelin in Anorexia Nervosa Extra doses don’t make people with anorexia eat more either.28PubMed Central. To eat or not to eat: A role for ghrelin and LEAP2 in eating disorders? Other effects seem intact, including heightened anxiety and constant preoccupation with food.29PubMed Central. To eat or not to eat: A role for ghrelin and LEAP2 in eating disorders?
That is why someone can think about food all day yet not eat. Preoccupation with recipes, cooking for others or watching food videos is common. It reflects the intact food-focus part of the hormone’s action, while the “eat now” part appears blocked. This is a starvation effect and usually eases as nutrition improves. Hunger cues are unreliable during illness and early recovery, so meals by the clock rather than by appetite are usually recommended.
Fat tissue also sends messages. It releases hormones that tell the brain how much energy is stored. Leptin, the main “energy stores are full” signal, is far lower in anorexia.30PubMed. Adipokines in anorexia nervosa: A systematic review and meta-analysis Adiponectin, another fat hormone, is higher.31PubMed Central. Comparison of Adiponectin Levels in Anorexia Nervosa, Bulimia Nervosa, Binge-Eating Disorder, Obesity, Constitutional Thinness, and Healthy Controls: A Network Meta-Analysis
Stress Hormones, Periods and Bone Loss
Cortisol is the body’s main stress hormone. It runs high in anorexia because starvation is a constant physical stress.32PubMed Central. Hypothalamic–pituitary–adrenal axis in anorexia nervosa; an underestimated endocrine dysfunction among adolescents Even though this follows from the eating disorder, high levels may help maintain the emotional and behavioral symptoms.33PubMed. The importance of the hypothalamo-pituitary-adrenal axis as a therapeutic target in anorexia nervosa Resting levels return to normal with weight gain.34Translational Psychiatry. Cortisol reactivity in patients with anorexia nervosa after stress induction The stress system’s response to a challenge, though, can stay blunted even at a recovered weight.35Translational Psychiatry. Cortisol reactivity in patients with anorexia nervosa after stress induction
Starvation also suppresses the brain signal that drives the menstrual cycle, so periods stop and estrogen drops.36Journal of Psychiatry and Brain Science. Estrogen for the Treatment of Low Bone Mineral Density in Anorexia Nervosa Thyroid hormones fall, a sign the body is slowing its metabolism to save energy.37PubMed. Hypothalamic-pituitary-thyroidal dysfunctions in anorexia nervosa Growth hormone rises, but the body stops responding to it, so its building effects are lost.38PubMed Central. THE ENDOCRINOPATHIES OF ANOREXIA NERVOSA These changes may help short-term survival yet cause lasting harm.39PubMed Central. Effects of Anorexia Nervosa on Bone Metabolism
People often notice the slowdown as feeling cold, tired and sluggish, with dry skin, thinning hair, constipation and slowed digestion. These usually improve as nutrition is restored.
Low estrogen speeds up the breakdown of bone, so the longer periods are absent, the lower bone density becomes.40Journal of Psychiatry and Brain Science. Estrogen for the Treatment of Low Bone Mineral Density in Anorexia Nervosa Bone loss affects more than 85% of women with anorexia and is often persistent.41PubMed Central. Effects of Anorexia Nervosa on Bone Metabolism Ask the care team about a bone density scan if periods have been absent for months.
Teenagers are building most of their lifetime bone, so losses then are harder to recover. Birth control pills can restart bleeding without fixing the underlying problem; weight restoration is what lets the natural cycle and bone building resume.
Effects on the Heart and Body Temperature
Up to 95% of people with anorexia develop a resting heart rate below 60 beats per minute.42PubMed Central. The Significance of Bradycardia in Anorexia Nervosa In one hospital group, about 7 in 10 had a rate below 50 at admission, with the lowest reaching 26.43PubMed Central. The Significance of Bradycardia in Anorexia Nervosa The slowing comes from changes in the nerves that control the heart, metabolic adaptation and loss of heart muscle.44PubMed. Cardiovascular Consequences of Anorexia Nervosa: QT Prolongation, Bradycardia, and Structural Cardiac Changes The muscle shrinks and pumps less blood, more than thinness alone explains.45PubMed Central. Assessment and management of cardiovascular complications in eating disorders
Severe cases can lead to fainting, low blood pressure and cardiac arrest.46PubMed. Cardiovascular Consequences of Anorexia Nervosa: QT Prolongation, Bradycardia, and Structural Cardiac Changes An irregular electrical pattern on heart tests appears in up to 40% of patients in some groups.47PubMed. Cardiovascular Consequences of Anorexia Nervosa: QT Prolongation, Bradycardia, and Structural Cardiac Changes Fainting, chest pain or a very slow pulse need urgent medical attention.
A slow pulse here is not a sign of fitness. Athletes have slow heart rates because their hearts are strong; in anorexia the heart is weakened. A home pulse reading can’t tell the difference, so doctors use heart tests and the overall picture to judge risk. A large jump in pulse on standing is another warning sign.
Core body temperature is lower in anorexia, around 35.4 to 36.6°C (95.7 to 97.9°F), versus a normal 37°C.48PubMed Central. Similarities and differences regarding acute anorexia nervosa and semi-starvation: does behavioral thermoregulation play a central role? The body cannot use its backup warming tools such as shivering, goosebumps or brown fat.49PubMed Central. Similarities and differences regarding acute anorexia nervosa and semi-starvation: does behavioral thermoregulation play a central role? Brown fat, which burns energy to make heat, is less active in women with anorexia.50PubMed Central. Young women with cold-activated brown adipose tissue have higher bone mineral density and lower Pref-1 than women without brown adipose tissue: a study in women with anorexia nervosa, women recovered from anorexia nervosa, and normal-weight women Feeling cold usually improves as weight and fat stores return.
What Heals With Recovery and What May Linger
Brain scans in anorexia commonly show loss of brain tissue, and the loss tracks how malnourished someone is.51Clinical Nutrition Experimental. Alterations of brain structure and functions in anorexia nervosa This loss is mostly reversible with recovery.52Clinical Nutrition Experimental. Alterations of brain structure and functions in anorexia nervosa Women who had recovered had normal amounts of the brain’s information-processing tissue.53PubMed Central. Normal gray matter volumes in women recovered from anorexia nervosa: a voxel-based morphometry study
In daily life, concentration and memory often improve as nutrition returns. Thinking may become less rigid and obsessive over months, and mood can improve, though anxiety traits may remain. Brain healing lags behind weight gain, so patience is needed.
Anorexia is linked to raised inflammation signals in the blood.54PubMed Central. Anorexia Nervosa and the Immune System—A Narrative Review After 6 months of combined therapy, medicine and nutrition, inflammation markers dropped significantly in teenage girls.55PubMed. Pro-inflammatory cytokine alterations in recent onset anorexia nervosa adolescent female patients before and after 6 months of integrated therapy: A case-control study Chemical tags that switch genes on or off change with malnutrition and appear to reverse once patients recover.56Springer Nature (Molecular Psychiatry). Epigenetic alterations in patients with anorexia nervosa—a systematic review
Some differences remain after weight is restored, including how the brain processes body signals and serotonin receptor patterns in some women.57PubMed Central. Altered Insula Activity during Visceral Interoception in Weight-Restored Patients with Anorexia Nervosa58JAMA Psychiatry. Altered Brain Serotonin 5-HT1A Receptor Binding After Recovery From Anorexia Nervosa Measured by Positron Emission Tomography and [Carbonyl11C]WAY-100635 Bone loss is often persistent.59PubMed Central. Effects of Anorexia Nervosa on Bone Metabolism Continued follow-up after weight returns is worthwhile.
Why Eating Again Has to Be Done Carefully
Refeeding syndrome is a dangerous shift in blood minerals when a starved body starts eating again.60PubMed Central. Starvation hepatitis and refeeding-induced hepatitis: mechanism, diagnosis, and treatment Long starvation drains phosphate, potassium and magnesium from inside cells even when blood tests look normal.61PubMed Central. Starvation hepatitis and refeeding-induced hepatitis: mechanism, diagnosis, and treatment When food returns, especially sugar and starch, insulin rises and cells pull these minerals out of the blood to rebuild.62PubMed Central. Starvation hepatitis and refeeding-induced hepatitis: mechanism, diagnosis, and treatment Very low phosphate can cause heart failure, muscle weakness and death.63PubMed. The refeeding syndrome and hypophosphatemia Low thiamine (vitamin B1) can cause serious brain problems.64PubMed Central. Refeeding syndrome: physiological background and practical management
The liver is affected too. In severe anorexia, liver cells can begin digesting themselves to survive, which can injure the liver.65PubMed Central. Liver Autophagy in Anorexia Nervosa and Acute Liver Injury Careful feeding with corrected blood sugar and minerals brought rapid liver improvement in severely ill patients.66PubMed Central. Liver Autophagy in Anorexia Nervosa and Acute Liver Injury Too much sugar too early can cause a different liver injury from fat and sugar buildup.67PubMed Central. Starvation hepatitis and refeeding-induced hepatitis: mechanism, diagnosis, and treatment
Safe early refeeding usually means a medical team sets the starting amounts and raises them step by step. Blood tests for phosphate, potassium and magnesium are checked often in the first days, and mineral and vitamin supplements are usually given. Severely underweight people may need hospital care for this stage. Swelling, weakness or confusion during refeeding need prompt medical review.