Eating Disorders: Anorexia, Bulimia, BED, ARFID — Diagnosis, Complications, Treatment

1. Historical Evolution of Eating Disorder Nosology

The modern understanding of eating disorders as distinct psychiatric entities emerged slowly from descriptions of "nervous consumption" and "anorexia nervosa" dating to the Victorian era.

2. DSM-5 Diagnostic Criteria and Current Nosology

Anorexia Nervosa (AN)

Core Criteria (all three required):

• Restriction of energy intake: Inadequate caloric intake relative to requirements, leading to significantly low body weight. DSM-5 specifies "significantly low body weight" without a specific BMI cutoff; <18.5 is often used as a guideline but not definitive. Some patients maintain "low-normal" BMI with psychological pathology.
• Intense fear of weight gain or persistent behavior that interferes with weight gain: Despite low weight, patient exhibits intense anxiety about weight gain or behaviors that actively prevent weight restoration. Unlike other phobias, fear may be ego-syntonic (patient views it as valid/adaptive).
• Disturbance in the way one's body weight or shape is experienced: Either denying seriousness of current low weight, or persistent behavioral/cognitive overvaluation of shape/weight in self-evaluation. Some patients exhibit complete denial ("I don't look thin"), others acknowledge weight loss but minimize its significance.

Subtypes: Restricting type (weight loss through dietary restriction alone) vs. Binge-Eating/Purging type (recurrent binge-eating and purging behaviors despite low weight).

Severity Specifier (based on current BMI): Mild (BMI ≥17), Moderate (16–16.99), Severe (15–15.99), Extreme (<15).

Bulimia Nervosa (BN)

Core Criteria (all three required):

• Recurrent episodes of binge eating: Discrete periods of eating objectively large quantities of food with subjective loss of control. Frequency criterion: at least once weekly for 3 months.
• Recurrent inappropriate compensatory behavior: Self-induced vomiting, laxative abuse, enemas, diuretics, fasting, or excessive exercise. The behavior is designed to prevent weight gain after a binge.
• Self-evaluation is unduly influenced by body shape and weight.

Critical Distinction from AN: Unlike AN with binge-eating/purging subtype, bulimia nervosa patients maintain normal or above-normal body weight. BMI is not part of diagnostic criteria for BN.

Severity (based on frequency of compensatory behavior): Mild (1–3 per week), Moderate (4–7 per week), Severe (8–13 per week), Extreme (≥14 per week).

Binge-Eating Disorder (BED)

Core Criteria (all three required):

• Recurrent episodes of binge eating: Same definition as BN; frequency ≥once weekly for 3 months. Binges are characterized by eating objectively large quantities with subjective loss of control.
• Associated with three or more of: Eating much more rapidly than normal; eating until uncomfortably full; eating large amounts despite absence of hunger; eating alone due to embarrassment; feeling disgusted, guilty, or depressed afterward.
• Marked distress regarding binge eating.

Key Distinction from BN: No regular compensatory behavior. BED patients binge but do not purge, fast, or exercise excessively in a compensatory manner. Most BED patients are overweight or obese; obesity is not part of diagnostic criteria but is the typical presentation.

Severity (based on binge frequency): Mild (1–3 per week), Moderate (4–7 per week), Severe (8–13 per week), Extreme (≥14 per week).

Avoidant/Restrictive Food Intake Disorder (ARFID)

Core Criteria (all four required):

• Restriction of intake in type and/or amount of food: As evidenced by inadequate intake and/or significant nutritional deficiency.
• Does not occur as a result of lack of available food or associated with another medical condition: Distinguishes from food insecurity and medical/gastrointestinal conditions.
• Does not occur exclusively during the course of anorexia nervosa, bulimia nervosa, binge-eating disorder, or avoidant/restrictive food intake disorder: Ensures distinct diagnostic category.
• Causing clinically significant impairment: In functioning, nutritional status, or distress.

Critical Feature: Lack of body-image disturbance. Unlike AN and BN, ARFID patients do not restrict food to change shape/weight and do not fear weight gain. Instead, food restriction stems from sensory sensitivity to food textures/tastes, anxiety about aversive consequences (choking, vomiting), or lack of interest in eating (early satiety, anhedonia). Pediatric patients with ARFID commonly have neophobia (fear of new foods) and texturally restrictive intake.

3. Medical Complications Across Organ Systems

Cardiac System

Structural Changes: Myocardial atrophy from prolonged caloric restriction. Chamber dilatation, particularly of the left atrium and left ventricle. Decreased left ventricular mass and diastolic function. These changes occur in proportion to degree of weight loss and malnutrition duration. Partial reversal occurs with nutritional rehabilitation, though complete remodeling may take months.

Electrical Dysfunction: Sinus bradycardia (heart rate <50 bpm is common, representing adaptive response to caloric restriction but indicating metabolic fragility). QT interval prolongation from hypokalemia and hypomagnesemia, creating vulnerability to torsades de pointes and sudden cardiac death. ST segment depression, T wave inversions. These ECG abnormalities correlate with sudden death risk in eating disorders.

Mitral Valve Prolapse (MVP): Occurs in 20–40% of AN patients, likely from cardiac remodeling and papillary muscle atrophy. Usually benign but increases arrhythmia risk in context of electrolyte dysregulation.

Clinical Monitoring: Baseline ECG mandatory; repeat as clinically indicated (severe electrolyte abnormalities, syncope, palpitations). Continuous cardiac monitoring during refeeding for high-risk patients. Electrolyte repletion before weight restoration to reduce arrhythmia risk.

Endocrine System

Hypothalamic Amenorrhea: One of the most striking features of severe AN. Hypothalamic hypogonadism from malnutrition results in suppression of GnRH, leading to suppression of LH and FSH. Amenorrhea or oligomenorrhea occurs in ~90% of menstruating females with AN. Amenorrhea typically resolves with weight restoration, though may lag by several months. Persistent amenorrhea despite weight restoration suggests hypothyroidism or hyperprolactinemia requiring investigation.

Low Estrogen State: Osteoporosis develops rapidly in young women with AN, with bone density losses of 2–3% per month during active disease. The combination of low estrogen, malnutrition, and elevated cortisol creates a perfect storm for bone loss. By age 30–40, many women with prior AN have osteoporosis-level bone density despite being relatively young. Fracture risk is elevated even among those who appear to have "recovered." Calcium, vitamin D, and weight restoration are essential.

Hypothyroidism and "Euthyroid Sick Syndrome": True autoimmune thyroiditis can occur. More commonly, malnutrition causes reduction in thyroid hormones and increased reverse T3, representing an adaptive slowing of metabolism. TSH is typically normal or low-normal. This "euthyroid sick syndrome" resolves with weight restoration and does not require thyroid replacement.

Elevated Cortisol: Chronic activation of the hypothalamic-pituitary-adrenal (HPA) axis from psychological stress and metabolic stress of malnutrition. This contributes to osteoporosis, myopathy, and immune dysfunction.

Gastrointestinal System

Gastroparesis: Delayed gastric emptying occurs in ~50% of AN patients. Stomach lining atrophies; smooth muscle loses contractility. Presents as early satiety, bloating, constipation, and subjective discomfort. Serious risk during refeeding if large meals are given; can lead to gastric rupture (rare, catastrophic). Treatment: small, frequent meals; prokinetic agents (metoclopramide, domperidone); rarely, total parenteral nutrition in extreme cases.

Constipation and Colonic Dysfunction: Profound constipation occurs in ~80% of AN patients from malnutrition, dehydration, and reduced GI motility. Use of laxatives is common among those engaging in purging; dependence and colonic dysfunction develop. Management: gradual refeeding with adequate fiber and hydration; weaning from laxatives during recovery.

Superior Mesenteric Artery (SMA) Syndrome: Rare but serious. Severe weight loss narrows the aortomesenteric angle, causing SMA to compress the duodenum, resulting in postprandial pain, vomiting, and obstruction. Can occur during refeeding as weight increases. Diagnosis by CT angiography; management conservative (small meals, prone positioning) or surgical in severe cases.

Renal System

Dehydration and Prerenal Azotemia: Severe dehydration from restricted fluid intake (and sometimes diuretic abuse). Serum creatinine and BUN elevated; ratio >20:1 suggests prerenal etiology. Corrects with fluid and nutritional repletion.

Chronic Kidney Disease: Rarely, prolonged malnutrition causes glomerulosclerosis and chronic kidney disease. More commonly seen in patients with decades of illness or comorbid conditions (diabetes if binging followed by hyperglycemic episodes).

Hematologic System

Pancytopenia: Malnutrition causes bone marrow suppression with reduction in all three cell lines. Anemia (often normocytic, reflecting chronic disease), leukopenia (increased infection risk), thrombocytopenia (bleeding risk). Counts typically recover with nutritional repletion.

Immunosuppression: Decreased lymphocyte count and function; altered complement system. Increased susceptibility to infection. Refeeding syndrome (see Section 4) is particularly dangerous because of immunosuppression; infections can rapidly become life-threatening.

Skeletal System

Osteoporosis and Osteopenia: Discussed above under endocrine. Bone density loss is among the most permanent complications of AN, persisting even after weight restoration and recovery. Long-term follow-up of recovered AN patients shows lifelong fracture risk elevation.

4. Refeeding Syndrome: Pathophysiology, Recognition, and Prevention

Refeeding syndrome represents one of medicine's most dangerous paradoxes: a life-threatening condition that emerges when treatment (nutritional rehabilitation) is begun. It occurs when severely malnourished patients receive rapid caloric repletion, causing abrupt shifts in electrolytes and phosphate metabolism.

Pathophysiology

During severe malnutrition, the body shifts to a catabolic state, depleting intracellular phosphate, potassium, and magnesium. Serum levels of these minerals may appear deceptively normal because of adaptive conservation mechanisms. When feeding is initiated, the body suddenly shifts from catabolism to anabolism: insulin secretion increases, driving intracellular uptake of glucose, phosphate, potassium, and magnesium. This creates a paradoxical scenario: serum electrolytes drop precipitously as they shift intracellularly.

Phosphate Shift: Hypophosphatemia (<2 mg/dL) occurs in up to 60% of patients with severe eating disorders beginning refeeding. Phosphate is essential for ATP production, red blood cell function, and cardiac contractility. Severe hypophosphatemia causes rhabdomyolysis (muscle breakdown), hemolysis, cardiac arrhythmias, respiratory failure, and death. Unlike hyperphosphatemia (which causes gradual complications), severe hypophosphatemia can be acutely fatal.

Hypokalemia: Serum potassium drops during refeeding, exacerbated if baseline levels were low. Hypokalemia causes arrhythmias (extending QT interval, torsades de pointes), weakness, and sudden cardiac death.

Hypomagnesemia: Often coexists with hypophosphatemia and hypokalemia. Impairs ATP synthesis, worsening cardiac and neuromuscular complications.

Clinical Recognition

Presentation (typically within 2–7 days of initiating refeeding): Palpitations, syncope or near-syncope, seizures, altered mental status, weakness, respiratory failure, shock. On examination: hypotension, tachycardia, arrhythmias. ECG shows QT prolongation, ST depression, peaked or inverted T waves. Laboratory: marked hypophosphatemia (<1.5 mg/dL is severe), hypokalemia, hypomagnesemia, hyperglycemia (from insulin resistance breaking down rapidly), elevated transaminases (from hepatic complications).

Prevention and Management

Baseline Assessment: Before initiating refeeding, obtain comprehensive metabolic panel (electrolytes, phosphate, magnesium, glucose), ECG, and TSH. Identify high-risk patients: BMI <14, rapid weight loss, duration of illness >5 years, purging behaviors, comorbid medical illness, age >40.

Slow Initial Refeeding: Critical strategy for prevention. Begin with 1,000–1,200 kcal/day (far below actual needs). Increase by 200–400 kcal every 3–5 days as tolerance permits. This gradual shift from catabolism to anabolism minimizes acute electrolyte shifts. Patience is essential; slow refeeding takes weeks and may require hospitalization.

Electrolyte Repletion: Empirically repleted before and during refeeding, even if serum levels appear normal. Phosphate replacement: 20–40 mmol per day (divided doses; IV preferred in severe cases, oral in milder). Potassium: 40–80 mEq per day (monitor levels closely, target >3.5). Magnesium: 6–12 g per day (often via IV in acute settings to ensure absorption).

Monitoring: Daily electrolytes (phosphate, potassium, magnesium, glucose) for first week, then every 2–3 days. Daily ECG for high-risk patients. Continuous cardiac monitoring if hospitalized. Thiamine and B vitamins supplementation (risk of Wernicke encephalopathy with refeeding in severely malnourished patients).

Stopping Diuretics and Laxatives: These must be discontinued before refeeding to prevent ongoing electrolyte losses.

5. Pharmacotherapy in Eating Disorders

Anorexia Nervosa: Limited Pharmacological Options

Antipsychotics for Weight Restoration: Olanzapine has the strongest evidence for AN, particularly for weight restoration in hospitalized patients. Mechanism: increased appetite, reduced compulsive exercising and obsessive thoughts about weight/shape. Randomized trials show weight gain acceleration and reduced anxiety during refeeding. Dose: 2.5–10 mg/day. Side effects (metabolic effects, akathisia) require careful monitoring. Cost and access remain barriers.

SSRIs Are NOT Effective for Acute AN: Multiple trials show SSRIs do not accelerate weight restoration in underweight patients. However, fluoxetine may reduce relapse risk during maintenance phase after weight restoration. Caution: SSRIs can increase suicide risk in vulnerable individuals; AN patients are at elevated suicide risk.

Cyproheptadine (Appetite Stimulant): Histamine H1 antagonist with appetite-stimulating properties. Modest evidence for weight gain, particularly in restricting subtype. Dose: 4–8 mg three times daily. Side effects: sedation, anticholinergic effects. Less effective than olanzapine but better tolerated.

Correction of Comorbidities: If depression, anxiety, or OCD symptoms persist after weight restoration, SSRIs or other psychotropics are appropriate. Treat hypothyroidism if present. Address calcium and vitamin D deficiency with supplementation.

Bulimia Nervosa: Strong SSRI Evidence

SSRIs Are First-Line Pharmacotherapy: Fluoxetine is FDA-approved for BN. Randomized trials show 50–70% reduction in binge-purge frequency compared to placebo. Higher doses are often required than for depression: fluoxetine 60 mg/day (compared to 20 mg for depression). Paroxetine (40–60 mg/day), sertraline (100–200 mg/day), and citalopram/escitalopram also have evidence.

Mechanism: Unclear, but SSRIs reduce impulsivity and mood dysregulation that triggers binges. May also affect hunger/satiety signaling.

Tricyclic Antidepressants: Imipramine and amitriptyline have older evidence but are less preferred due to side effects (anticholinergic effects, arrhythmia risk in context of electrolyte dysregulation). Rarely used in modern practice.

Topiramate: Off-label evidence suggests modest benefit for reducing binge-purge frequency and associated weight gain. Mechanism unclear. Side effects (cognitive impairment, paresthesias) limit use. Avoid due to potential appetite suppression in context of restrictive eating.

Binge-Eating Disorder: SSRI and Lisdexamfetamine Evidence

SSRIs: Fluoxetine, sertraline, citalopram show efficacy in reducing binge frequency and associated psychopathology. Doses similar to BN. Modest effect sizes; not all patients respond.

Lisdexamfetamine (Vyvanse): FDA-approved for BED. Stimulant that increases dopamine and norepinephrine. Reduces binge frequency and severity. Dose: 30–70 mg/day. Side effects: insomnia, anxiety, cardiovascular effects. Contraindicated in patients with active substance use disorder.

GLP-1 Receptor Agonists (Semaglutide, Tirzepatide): Emerging evidence suggests benefit for BED and weight loss. Mechanism: enhanced satiety signaling. Use with caution in eating disorder populations; potential for overuse and harm if patient develops restrictive behaviors around medication.

ARFID: Limited Pharmacotherapy

No FDA-approved medications specifically for ARFID. Treatment is primarily behavioral (exposure-based therapy, graduated exposure to feared foods). SSRIs may help comorbid anxiety (social anxiety, generalized anxiety) that may be maintaining food avoidance.

6. Evidence-Based Psychotherapies

Family-Based Treatment (FBT) for Adolescent Anorexia Nervosa

Gold Standard for Adolescents: FBT (also called "Maudsley method") is the most empirically-supported treatment for adolescent AN. The approach places parents at the center of treatment, empowering them to manage their child's eating and weight restoration. The therapist coaches parents rather than directly treating the adolescent.

Rationale: Adolescence is a period of rapid development and neural plasticity. Parents are the most consistent environmental influence. By the time adolescents develop full-syndrome AN, their own insight is often impaired (ego-syntonic symptoms); redirecting control to parents often proves more effective than individual psychotherapy.

Structure: Three phases over 12–20 sessions: (1) Reestablishing Parental Control (parents take full responsibility for meals and weight restoration, reducing focus on the adolescent's cooperation); (2) Returning Control to the Adolescent (as weight increases and insight returns, responsibility gradually returns); (3) Addressing Remaining Issues (broader psychosocial functioning, relapse prevention).

Outcomes: 50–60% full remission; 80–90% significant improvement. Superior to individual psychotherapy in adolescents. Less effective in adults, whose families may have longer-standing dysfunction.

Cognitive-Behavioral Therapy–Enhanced (CBT-E)

Transdiagnostic Approach: CBT-E was developed specifically for eating disorders and addresses the core cognitive distortions (overvaluation of appearance/weight, dichotomous thinking about food/control) across all eating disorder categories. Can be adapted for outpatient (16 weeks) or intensive (20 weeks) formats.

Core Components: Psychoeducation about eating disorder maintenance mechanisms; monitoring food intake and associated thoughts/feelings; behavioral experiments (eating feared foods, reducing compensatory behaviors); cognitive restructuring (challenging body-image distortions and perfectionism); problem-solving for triggers; relapse prevention.

Outcomes: 60–70% remission in BN and BED (superior to antidepressants alone or in combination). Less effective in AN, particularly severe AN, without accompanying intensive nutritional rehabilitation. Often combined with family therapy in adolescents.

Interpersonal Therapy (IPT)

Evidence in BED and BN: IPT addresses interpersonal relationships, grief, role transitions, and interpersonal disputes that maintain binge-eating. Not a first-line approach but effective for patients with prominent interpersonal dysfunction or limited access to specialized CBT-E.

Dialectical Behavior Therapy (DBT)

For eating disorders with prominent emotion dysregulation, impulsivity, or self-harm, DBT elements (mindfulness, distress tolerance, emotion regulation skills) may be integrated into treatment, though dedicated DBT for eating disorders requires specialized training.

7. Special Populations and Atypical Presentations

Males with Eating Disorders

Epidemiology: ~25–40% of BED patients are male; ~10–20% of BN and AN patients are male. Males are vastly underdiagnosed due to: (1) diagnostic criteria developed in female populations, (2) clinician bias (eating disorders viewed as female illnesses), (3) different presentation (males focus on muscularity/"bulk" rather than thinness; may overexercise for mass gain), (4) shame and stigma.

Clinical Presentation Differences: Males are more likely to have BED as primary disorder. When AN occurs, may focus on muscularity and maintain reasonable weight while undereating and over-exercising (termed "muscle dysmorphia"). Some males describe muscle gain as primary goal (as opposed to weight loss in females). Treatment approaches must be adapted; FBT and CBT-E remain effective but require language adjustments (focusing on performance and strength rather than appearance).

Athletes with Eating Disorders

Relative Energy Deficiency in Sport (RED-S): Encompasses eating disorders in athletes, but also subclinical undereating in context of high energy expenditure. Affects multiple physiological systems: menstrual dysfunction (females), reduced testosterone (males), impaired bone health, impaired immune function, increased injury risk. May not meet full diagnostic criteria for eating disorder but has serious medical consequences.

Clinical Challenge: Distinguishing between healthy athlete training and disordered eating is difficult. Coaches, trainers, and even athletes themselves may normalize restrictive eating as "necessary for performance." Treatment requires multidisciplinary team (physician, psychiatrist, nutritionist, coach) to address both athletic and psychiatric needs.

8. Prognosis Across the Lifespan and Monitoring

Anorexia Nervosa: ~50–60% full recovery; ~20–30% partial recovery; ~5–6% per decade mortality. Earlier age of onset, shorter duration before treatment, and higher premorbid functioning predict better outcomes. Adults with long-standing illness have poorer prognosis than adolescents.

Bulimia Nervosa: Better prognosis than AN. ~50–70% remission with appropriate treatment; ~20–30% partial improvement. Purging-related medical complications (esophageal damage, dental erosion, hypokalemia) may be permanent.

Binge-Eating Disorder: Better prognosis than AN or BN. ~50–60% remission; associated weight loss and metabolic improvement with successful treatment.

Monitoring During Recovery: Regular medical monitoring includes: cardiac assessments (ECG for QT prolongation and arrhythmias); electrolyte panels (weekly initially, then biweekly/monthly); bone density screening (DEXA); endocrine function (TSH, reproductive hormones); nutritional status (weight, BMI, albumin, prealbumin). Psychological monitoring includes: assessment of mood, suicidality, and eating disorder symptoms (using validated scales like Eating Disorder Examination–Questionnaire). Nutritional rehabilitation should continue through recovery to prevent relapse.