63.3 Eating Disorders: Anorexia Nervosa, Bulimia & Binge Eating
Key Takeaways
- Anorexia Nervosa (AN) requires restriction of energy intake leading to significantly low body weight (BMI <18.5 kg/m2 in adults or <5th percentile in children), intense fear of weight gain, and distorted body perception; physical findings include cachexia, hypothermia (<35°C), bradycardia (<40-50 bpm), lanugo hair, parotid sialadenosis, Russell sign, and euthyroid sick syndrome.
- Indications for immediate medical hospitalization in anorexia nervosa include heart rate <40 bpm, systolic blood pressure <90 mmHg (or orthostatic SBP drop >20 mmHg), body weight <75% of expected (BMI <15 kg/m2), body temperature <35.5°C (96°F), serum potassium <3.0 mEq/L, severe hypophosphatemia, and QTc prolongation (>460 ms).
- Refeeding syndrome is a fatal complication triggered by carbohydrate reintroduction in a starved patient; massive insulin release drives phosphate, potassium, and magnesium into cells to power glycolysis and ATP synthesis, causing profound hypophosphatemia, respiratory failure, cardiac arrest, and rhabdomyolysis; prevention requires slow caloric advancement (10-20 kcal/kg/day), frequent electrolyte monitoring, and pre-feeding thiamine administration.
- Bulimia Nervosa (BN) features recurrent binge eating with inappropriate compensatory behaviors occurring at least once weekly for 3 months in a normal or overweight patient (BMI ≥18.5 kg/m2; BMI <18.5 defines binge/purge anorexia); high-dose fluoxetine (60 mg daily) is the only FDA-approved medication, while bupropion is STRICTLY CONTRAINDICATED in both bulimia and anorexia due to elevated grand mal seizure risk.
- Binge-Eating Disorder (BED) is characterized by recurrent binge eating WITHOUT compensatory purging; first-line therapy is Cognitive Behavioral Therapy (CBT), and lisdexamfetamine (Vyvanse 50-70 mg daily) is the only FDA-approved pharmacotherapy for moderate-to-severe BED.
Spectrum of Eating Disorders in Primary Care
Eating disorders are severe psychiatric illnesses characterized by persistent disturbances in eating behaviors paired with distressing thoughts and emotions regarding weight, body shape, and food intake. They carry among the highest mortality rates of any psychiatric disorder group, driven by acute medical complications (arrhythmias, refeeding syndrome, metabolic collapse) and suicide. Family physicians serve as the frontline defense in detecting subclinical eating pathology, conducting physical and laboratory risk stratification, preventing life-threatening refeeding complications, and coordinating multidisciplinary outpatient or inpatient care.
Anorexia Nervosa (AN)
Anorexia Nervosa is a life-threatening illness characterized by pathological pursuit of thinness, severe caloric restriction, and profound body image distortion. It predominantly affects adolescent females and young women (female-to-male ratio ~10:1), though it occurs in males, diverse gender identities, and older adults.
DSM-5 Diagnostic Criteria for Anorexia Nervosa
A formal DSM-5 diagnosis requires all three core criteria:
- Restriction of Energy Intake: Caloric restriction relative to requirements leading to a significantly low body weight in the context of age, sex, developmental trajectory, and physical health. Significantly low weight is defined as a weight less than minimally normal:
- Adults: Body Mass Index (BMI) < 18.5 kg/m².
- Children & Adolescents: BMI < 5th percentile for age and sex, or a failure to maintain expected growth trajectory.
- Intense Fear of Gaining Weight: Intense fear of gaining weight or becoming fat, or persistent behavior that interferes with weight gain, even though at a significantly low weight.
- Disturbance in Self-Perception: Disturbance in the way in which one's body weight or shape is experienced, undue influence of body weight/shape on self-evaluation, or persistent lack of recognition of the seriousness of the current low body weight.
ANOREXIA NERVOSA SUBTYPES & SEVERITY STAGING
Diagnostic Subtype Operational Definition & Clinical Characteristics
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Restricting Type During the last 3 months, the individual has NOT engaged in recurrent
episodes of binge eating or purging (self-induced vomiting or misuse of
laxatives, diuretics, or enemas). Weight loss is accomplished primarily
through dieting, fasting, and/or excessive, compulsive exercise.
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Binge-Eating / Purging During the last 3 months, the individual HAS engaged in recurrent episodes
Type of binge eating or purging behavior (self-induced vomiting, laxative abuse,
diuretics, or enemas) WHILE MAINTAINING A SIGNIFICANTLY LOW BODY WEIGHT.
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Severity Staging (Adults) • Mild: BMI ≥ 17.0 kg/m²
• Moderate: BMI 16.0 - 16.99 kg/m²
• Severe: BMI 15.0 - 15.99 kg/m²
• Extreme: BMI < 15.0 kg/m² (Immediate Medical Hospitalization Mandatory)
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Exam Pearl: The presence of amenorrhea was eliminated as an obligate diagnostic criterion in DSM-5. This modification prevents the exclusion of pre-menarcheal girls, postmenopausal women, males, and females taking oral contraceptive pills.
Physical Examination & Clinical Findings
Chronic starvation and purging induce multi-organ physiological decompensation:
CLINICAL SIGNS OF ANOREXIA NERVOSA
Physiological System Clinical Manifestations & Diagnostic Signs
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Vital Signs • Hypothermia: Core body temperature < 35.0°C (95.0°F).
• Sinus Bradycardia: Resting heart rate < 40-50 beats/min.
• Hypotension: Resting blood pressure < 90/60 mmHg.
• Orthostasis: SBP drop > 20 mmHg, DBP drop > 10 mmHg, or HR rise > 20 bpm.
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Dermatologic & Hair • Lanugo Hair: Growth of fine, downy, unpigmented hair over back, face, arms
(physiological adaptation to conserve core body heat).
• Xerosis & Hypercarotenemia: Dry, scaly skin; yellow-orange pigmentation of
palms and soles (due to impaired hepatic conversion of carotene to vitamin A).
• Acrocyanosis: Cold, bluish discoloration of hands and feet (peripheral vasoconstriction).
• Brittle nails and diffuse telogen effluvium (hair shedding).
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Head, Neck & Oral • Salivary Gland Hypertrophy (Sialadenosis): Painless, bilateral enlargement of
parotid and submandibular glands (autonomic stimulation from vomiting).
• Perimylolysis: Severe, smooth erosion of dental enamel on the lingual/palatal
surfaces of maxillary teeth caused by recurrent gastric hydrochloric acid exposure.
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Extremities • Russell Sign: Calluses, hyperkeratoses, or abrasions on the dorsal surface of
the hand/knuckles from repeated trauma against incisors during manual self-emesis.
• Peripheral Dependent Edema: Starvation hypoalbuminemia, fluid shifts, or refeeding.
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Laboratory & Diagnostic Derangements
Starvation and purging alter almost every biochemical and hematologic parameter:
- Hematology: Gelatinous marrow transformation (starvation marrow hypoplasia) produces leukopenia with absolute neutropenia (most common), normocytic normochromic anemia, and thrombocytopenia. Pancytopenia resolves completely upon weight restoration.
- Endocrine / Metabolic Derangements:
- Euthyroid Sick Syndrome (Non-Thyroidal Illness): Characterized by low total and free T3, normal-to-low T4, and a normal TSH. This represents an adaptive hypometabolic response to starvation. Levothyroxine replacement is strictly contraindicated, as administering exogenous thyroid hormone induces catabolism and precipitates acute cardiac arrest.
- Hypogonadotropic Hypogonadism: Starvation blunts hypothalamic gonadotropin-releasing hormone (GnRH) pulsatility, leading to suppressed luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol/testosterone levels (functional hypothalamic amenorrhea).
- Hypercholesterolemia: Total cholesterol and LDL cholesterol are paradoxically elevated due to blunted hepatic catabolism and reduced biliary excretion of cholesterol esters during starvation.
- Electrolyte Derangements:
- Vomiting / Purging: Hypokalemic, hypochloremic metabolic alkalosis with elevated serum bicarbonate (loss of gastric HCl paired with secondary hyperaldosteronism driven by volume depletion).
- Laxative Misuse: Hypokalemic, hyperchloremic normal anion-gap metabolic acidosis (loss of alkaline bicarbonate-rich fluid from the colon).
- Excessive Water Loading: Profound dilutional hyponatremia predisposing to cerebral edema and status epilepticus.
- Cardiovascular: Electrocardiogram (ECG) reveals sinus bradycardia, low voltage, T-wave flattening or inversion, and dangerous QTc interval prolongation (>460 ms) predisposing to fatal ventricular dysrhythmias (Torsades de Pointes).
- Skeletal (Osteopenia & Osteoporosis): Up to 85% of patients exhibit osteopenia and 40% develop osteoporosis. Driven by hypercortisolemia, IGF-1 deficiency, and sex steroid deficiency. Dual-energy X-ray absorptiometry (DEXA) is indicated in any patient with underweight status or amenorrhea persisting ≥6 months. Oral contraceptive pills do NOT restore bone density in anorexia nervosa; nutritional rehabilitation and spontaneous resumption of menses is the only effective therapy.
Indications for Immediate Medical Hospitalization
The Academy for Eating Disorders (AED) and American Psychiatric Association (APA) mandate immediate inpatient medical admission for patients meeting ANY of the following objective criteria:
INDICATIONS FOR IMMEDIATE MEDICAL HOSPITALIZATION
Clinical Domain Threshold Mandating Immediate Medical Admission
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Heart Rate • Resting heart rate < 40 beats per minute
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Blood Pressure • Systolic blood pressure < 90 mmHg OR Diastolic BP < 60 mmHg
• Orthostatic SBP drop > 20 mmHg, DBP drop > 10 mmHg, or HR rise > 20 bpm
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Body Weight / BMI • Body weight < 75% of median expected body weight for age/height
• BMI < 15.0 kg/m²
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Body Temperature • Core body temperature < 35.5°C (96.0°F)
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Electrolyte Derangements • Serum Potassium < 3.0 mEq/L
• Serum Phosphorus < 2.5 mg/dL
• Serum Magnesium < 1.4 mg/dL
• Severe hyponatremia (< 125 mEq/L) or hypernatremia
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Cardiac Conduction • QTc interval > 460 ms (males) or > 470 ms (females)
• Sustained cardiac dysrhythmias or AV block
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Acute Clinical Status • Acute food refusal, uncontrolled purging, syncope, acute hematemesis
• Acute psychiatric emergency: active suicidality or psychosis
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Refeeding Syndrome: Pathophysiology & Prevention Protocol
Refeeding syndrome is a potentially fatal constellation of metabolic and electrolyte shifts occurring when nutrition (specifically carbohydrates) is reintroduced to a severely malnourished, starved patient.
PATHOPHYSIOLOGY OF REFEEDING SYNDROME
Prolonged Starvation ──> Total-Body Phosphate, Potassium & Magnesium Depletion
(Serum levels falsely normal due to hemoconcentration)
│
Reintroduction of Carbohydrates ────┘
│
▼
Massive Surge in Endogenous Insulin Secretion
│
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│ │
▼ ▼
Intracellular Shifting of Phosphate, Potassium & Mg Renal Sodium & Water Retention
• Required for glycolysis & ADP ──> ATP synthesis (Insulin stimulates renal tubule)
│ │
┌───────────┴──────────────────────────────┐ │
▼ ▼ ▼
PROFOUND HYPOPHOSPHATEMIA Hypokalemia & Hypo-Mg Refeeding Edema
• Severe ATP & 2,3-DPG depletion • Ventricular Arrhythmias • Congestive Heart Failure
• Diaphragmatic Respiratory Failure • Torsades de Pointes • Pulmonary Edema
• Acute Rhabdomyolysis & Seizures • Neuromuscular Tetany • Fluid Overload
• Cardiac Arrest & Death
The Refeeding Syndrome Prevention & Management Protocol
- Pre-Feeding Electrolyte Repletion: Obtain baseline serum phosphorus, potassium, and magnesium. Aggressively replete deficient electrolytes intravenously or orally before initiating caloric intake.
- Mandatory Pre-Feeding Thiamine Administration:
- Thiamine (Vitamin B1) 100 to 200 mg daily IV or PO must be administered BEFORE feeding begins and continued for at least 3 to 5 days.
- Rationale: Thiamine pyrophosphate is an obligate cofactor for pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase in carbohydrate glycolysis. Reintroducing carbohydrates in a thiamine-deficient patient precipitates acute Wernicke Encephalopathy (triad: encephalopathy, ophthalmoplegia/nystagmus, ataxia) or wet beriberi (high-output heart failure).
- Start Low and Advance Slow:
- Initiate caloric intake conservatively at 10 to 20 kcal/kg/day (typically 1,000 to 1,200 kcal/day in adults).
- Advance caloric density gradually by 200 to 300 kcal every 2 to 3 days based on clinical stability and daily laboratory values.
- Intensive Biochemical Surveillance:
- Check serum phosphorus, potassium, magnesium, sodium, and renal function every 12 to 24 hours for the first 7 to 14 days of nutritional rehabilitation.
Bulimia Nervosa (BN)
Bulimia Nervosa is characterized by recurrent cycles of binge eating followed by inappropriate compensatory behaviors designed to prevent weight gain.
DSM-5 Diagnostic Criteria for Bulimia Nervosa
A formal diagnosis requires meeting all five criteria:
- Recurrent Binge Eating: Consuming, in a discrete period (e.g., within 2 hours), an amount of food definitely larger than what most individuals would eat in similar circumstances, accompanied by a subjective sense of lack of control during the episode.
- Inappropriate Compensatory Behaviors: Recurrent behaviors to prevent weight gain, including self-induced vomiting, misuse of laxatives, diuretics, or enemas, fasting, or compulsive excessive exercise.
- Frequency & Duration: Both binge eating and inappropriate compensatory behaviors occur, on average, at least once a week for 3 months.
- Undue Influence of Shape/Weight: Self-evaluation is unduly influenced by body shape and weight.
- Weight Distinction: The disturbance does not occur exclusively during episodes of anorexia nervosa.
[!IMPORTANT] The Critical Weight Threshold Differentiating BN from AN: Patients with Bulimia Nervosa maintain a normal or above-normal body weight (BMI ≥ 18.5 kg/m²). If a patient meets all symptom criteria for bulimia but has a BMI < 18.5 kg/m², the formal diagnosis is Anorexia Nervosa, Binge-Eating/Purging Type, NOT Bulimia Nervosa! Anorexia nervosa always supersedes bulimia nervosa.
Evidence-Based Treatment of Bulimia Nervosa
1. First-Line Psychotherapy: Cognitive Behavioral Therapy (CBT-ED)
- CBT for Eating Disorders (CBT-ED) is the non-pharmacologic gold standard, demonstrating the highest rates of binge-purge cessation and long-term maintenance of remission. It targets dysfunctional cognitive dietary restraint, body shape over-evaluation, and emotional triggers for binge episodes.
2. First-Line Pharmacotherapy: High-Dose Fluoxetine
- Fluoxetine (Prozac) is the ONLY FDA-approved medication for bulimia nervosa.
- Dosing: Titrate to 60 mg orally once daily in the morning. Randomized double-blind trials proved that the standard antidepressant dose (20 mg daily) is clinically ineffective for bulimia; the 60 mg daily dose is required to significantly reduce binge-eating and purge frequency.
3. Strict Black-Box Contraindication: Bupropion in Bulimia & Anorexia
[!CAUTION] Bupropion (Wellbutrin) is ABSOLUTELY CONTRAINDICATED in patients with active or historical Bulimia Nervosa or Anorexia Nervosa.
- Severe Seizure Risk: Clinical trials and post-marketing safety data demonstrated an unacceptably high incidence of grand mal epileptic seizures in patients with eating disorders receiving bupropion.
- Mechanism: Acute starvation, fluid shifts, and electrolyte imbalances (hypokalemia, hypomagnesemia, alkalosis) lower the baseline seizure threshold. Bupropion inhibits neuronal norepinephrine and dopamine reuptake, lowering seizure thresholds in a dose-dependent fashion and triggering life-threatening status epilepticus.
Binge-Eating Disorder (BED)
Binge-Eating Disorder is the most common eating disorder in the United States, affecting 2-3% of adults. It affects males and females more equally than AN or BN (approximately 60% female, 40% male) and is strongly associated with class I-III obesity, metabolic syndrome, major depression, and generalized anxiety.
DSM-5 Diagnostic Criteria for Binge-Eating Disorder
Diagnosis requires all five criteria:
- Recurrent Episodes of Binge Eating: Eating in a discrete time period an amount of food definitely larger than normal with a subjective sense of lack of control.
- Associated Features (≥ 3 of the following 5):
- Eating much more rapidly than normal.
- Eating until feeling uncomfortably full.
- Eating large amounts of food when not feeling physically hungry.
- Eating alone because of feeling embarrassed by how much one is eating.
- Feeling disgusted with oneself, depressed, or very guilty afterward.
- Marked Distress: Marked personal distress regarding binge eating.
- Frequency & Duration: Occurs, on average, at least once a week for 3 months.
- ABSOLUTE ABSENCE OF COMPENSATORY BEHAVIORS: The binge eating is NOT associated with recurrent inappropriate compensatory behaviors (no vomiting, laxative abuse, fasting, or compulsive exercise).
DIAGNOSTIC COMPARISON: AN VS. BN VS. BED
Feature Anorexia Nervosa (B/P) Bulimia Nervosa Binge-Eating Disorder
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Body Mass Index (BMI) < 18.5 kg/m² (Underweight) ≥ 18.5 kg/m² (Normal/High) Typically ≥ 25-30 (Overweight/Obese)
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Recurrent Binge Eating? YES (in B/P subtype) YES YES
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Compensatory Purging? YES (Vomiting, laxatives) YES (Vomiting, laxatives) NO (STRICTLY ABSENT)
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Body Image Distortion? PROFOUND / Severe PROFOUND / Severe Distress, but less distortion
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First-Line Psychotherapy Family-Based / CBT CBT-ED CBT
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FDA-Approved Medication NONE Fluoxetine (60 mg daily) Lisdexamfetamine (50-70 mg)
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Strictly Contraindicated Bupropion (Seizure risk) Bupropion (Seizure risk) None specific
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Evidence-Based Treatment of Binge-Eating Disorder
1. First-Line Psychotherapy: Cognitive Behavioral Therapy (CBT)
- CBT is the established non-pharmacologic first-line treatment for BED, demonstrating superior efficacy in reducing binge frequency, eliminating shame, and promoting dietary regularity. However, CBT alone produces modest weight loss; comprehensive management often incorporates behavioral weight loss programs.
2. First-Line Pharmacotherapy: Lisdexamfetamine (Vyvanse)
- Lisdexamfetamine is the ONLY FDA-approved medication for moderate-to-severe Binge-Eating Disorder in adults.
- Mechanism: A central nervous system sympathomimetic prodrug of dextroamphetamine. Enhances presynaptic release and blocks reuptake of norepinephrine and dopamine in the prefrontal cortex and hypothalamus, suppressing hunger signaling, reducing binge impulsivity, and promoting executive control over food intake.
- Dosing Protocol: Initiate at 30 mg orally once daily in the morning. Titrate by 20 mg weekly increments to the target maintenance dose of 50 to 70 mg daily.
- Adverse Effects & Monitoring: Insomnia, dry mouth, decreased appetite, tachycardia, hypertension, and anxiety. Monitor resting blood pressure and heart rate at every clinical encounter. Contraindicated in uncontrolled hypertension, active cardiovascular disease, hyperthyroidism, glaucoma, history of stimulant misuse, or concurrent MAOI use.
3. Second-Line & Off-Label Pharmacotherapies
- Topiramate (Off-Label): An anticonvulsant and GABA modulator that significantly reduces binge frequency and promotes meaningful weight loss. However, clinical utility is limited by adverse effects: cognitive slowing ('dopamax'), somnolence, paresthesias, taste perversion (metallic taste with carbonated drinks), metabolic acidosis, and calcium phosphate nephrolithiasis.
- SSRIs (Off-Label; Sertraline, Fluoxetine): Provide short-term reductions in binge eating and treat comorbid depressive or anxiety disorders, but do not produce sustained long-term weight reduction.
A 17-year-old high school cross-country runner is brought to the outpatient clinic by her mother due to extreme weight loss, lightheadedness, and progressive lethargy. Her mother notes that she exercises for 3 hours daily, eats only small portions of celery and raw egg whites, and panics when urged to eat carbohydrates. On physical examination, she appears severely emaciated with temporal wasting, dry scaly skin, and fine downy hair over her back and arms. Her height is 165 cm (5 ft 5 in) and her weight is 38 kg (83.8 lb), corresponding to a BMI of 13.9 kg/m². Her vital signs are temperature 35.1°C (95.2°F), blood pressure 82/52 mmHg with an orthostatic systolic drop of 24 mmHg upon standing, and a resting heart rate of 36 beats per minute. An electrocardiogram reveals profound sinus bradycardia with a corrected QT interval of 478 ms. What is the most appropriate immediate setting of care for this patient, and what pathophysiological complication represents the greatest risk during initial nutritional rehabilitation?
A 23-year-old graduate student presents to the primary care clinic for an annual examination. During the interview, she tearfully confides that for the past 6 months, she has engaged in uncontrollable binge-eating episodes 3 to 4 times per week, during which she consumes entire boxes of pastries and ice cream within an hour. Following each episode, overwhelmed by intense guilt and panic over potential weight gain, she induces vomiting by gagging herself with her fingers. She reports that her self-esteem is entirely dependent on her body shape and scale weight. On examination, her BMI is 22.4 kg/m². Physical examination reveals bilateral painless enlargement of the parotid glands, mild dental enamel erosion on the lingual surfaces of the upper teeth, and calluses on the dorsal aspect of her right hand over the metacarpophalangeal joints. Basic metabolic panel reveals a serum potassium of 3.2 mEq/L, serum chloride of 92 mEq/L, and bicarbonate of 31 mEq/L. In addition to referring her for cognitive behavioral therapy, which pharmacotherapeutic agent is FDA-approved for her condition, and which antidepressant is strictly contraindicated?
A 38-year-old male presents to his family physician to discuss weight management and emotional distress. Over the past 9 months, he has experienced recurrent episodes roughly 3 times per week where he consumes massive quantities of food (such as two large pizzas, a family-size bag of chips, and two liters of soda) within a 90-minute period late at night. He describes a complete lack of control during these episodes, eating rapidly until he feels painfully distended, eating even when not physically hungry, and hiding food wrappers in the garage out of intense shame. He explicitly denies ever inducing vomiting, using laxatives, fasting, or engaging in excessive exercise. His medical history includes hypertension and class II obesity (BMI 36.8 kg/m²). Physical examination is unremarkable aside from obesity, with a blood pressure of 126/78 mmHg and heart rate of 72 bpm. Which of the following is the most accurate diagnosis and the most appropriate evidence-based first-line management strategy for this patient?