Nutrition
Clinical Nutrition — Comprehensive
Nutrition

Clinical Nutrition — Comprehensive

Refeeding, micronutrient deficiencies/toxicities, TPN, malnutrition assessment, eating disorders.

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◆Refeeding syndrome

  • •Trigger: carbohydrate reintroduction in malnourished/starved patient → insulin surge
  • •Insulin drives PO₄, K, Mg INTO cells
  • •HALLMARK: severe HYPOPHOSPHATEMIA → ATP depletion → respiratory failure + arrhythmias
  • •Prevention: thiamine BEFORE feeding, start low-calorie (~25% goal), advance slowly, replete electrolytes
  • •High-risk: severe malnutrition, prolonged starvation, alcohol use disorder, anorexia nervosa, hyperemesis

◆Thiamine (B1) deficiency

  • •Wernicke triad: confusion + ophthalmoplegia/nystagmus + ataxia (REVERSIBLE)
  • •Korsakoff: amnesia + confabulation (PERMANENT)
  • •Always give IV thiamine BEFORE glucose in malnourished
  • •High-risk: alcoholism, hyperemesis gravidarum, anorexia, post-bariatric, starvation
  • •Wet beriberi: high-output HF + edema
  • •Dry beriberi: peripheral neuropathy

◆B12 (cobalamin) deficiency

  • •Causes: pernicious anemia (anti-IF), metformin (impairs Ca-dependent absorption in terminal ileum), chronic PPIs, ileal resection >60 cm (lifelong IM)
  • •Megaloblastic anemia + neuro (subacute combined degeneration of dorsal columns + corticospinal)
  • •↑ MMA + ↑ homocysteine
  • •Folate deficiency: ↑ homocysteine ONLY (no neuro, normal MMA)
  • •Always give B12 BEFORE folate (folate alone worsens neuro symptoms)

◆Copper deficiency (post-bariatric, excess zinc)

  • •Absorbed in stomach + proximal duodenum (bypassed in RYGB)
  • •Mimics B12: posterior column signs (vibration, proprioception, +Romberg)
  • •DISTINGUISHING feature: NEUTROPENIA + anemia
  • •Normal B12 in copper deficiency
  • •Excess zinc supplementation can also cause copper deficiency

◆TPN complications

  • •Hepatic steatosis + cholestasis within 1–4 weeks
  • •Biliary stasis → sludge/stones (no enteral stimulation = ↓ CCK)
  • •CLABSI: most dangerous infection (central line)
  • •Trace element deficiencies emerge with long-term TPN:
  • • Selenium → dilated cardiomyopathy + skeletal myopathy
  • • Chromium → refractory hyperglycemia
  • • Zinc → dermatitis + diarrhea + alopecia (acrodermatitis enteropathica)
  • •Refeeding risk with TPN initiation

◆Other micronutrients (high yield)

  • •Vitamin A: deficiency → night blindness + xerophthalmia + Bitot spots; toxicity → pseudotumor cerebri + hepatotoxicity; teratogenic (isotretinoin → craniofacial/CNS/cardiac)
  • •Vitamin D: deficiency → rickets/osteomalacia; toxicity → hyperCa + hyperphosphate + SUPPRESSED PTH (vs primary hyperparathyroidism: low PO4)
  • •Vitamin E: deficiency → posterior column + spinocerebellar degeneration + hemolytic anemia
  • •Vitamin C: scurvy — bleeding/swollen gums, perifollicular hemorrhages, corkscrew hairs, poor wound healing
  • •Vitamin K: deficiency → bleeding; warfarin interaction — dietary CONSISTENCY, not avoidance
  • •Zinc: acrodermatitis enteropathica, hypogeusia, hypogonadism
  • •Iodine: goiter, hypothyroidism, cretinism (pregnancy)
  • •Selenium: TPN → dilated CM; thyroid dysfunction

◆TPN trace element pattern recognition

  • •TPN + cardiomyopathy → Selenium
  • •TPN + refractory hyperglycemia → Chromium
  • •TPN + dermatitis + diarrhea + alopecia → Zinc
  • •TPN + neuropathy/anemia + neutropenia → Copper
  • •Maternal goiter + hypothyroid infant → Iodine
  • •Refractory hypokalemia → Magnesium

◆Drug-nutrient interactions (high-yield)

  • •PPIs → ↓ Mg, Ca, B12 absorption
  • •Metformin → B12 deficiency
  • •Isoniazid → B6 deficiency (give B6 to prevent peripheral neuropathy + sideroblastic anemia)
  • •Loop diuretics → K + Mg wasting; replete Mg before K
  • •Orlistat → fat-soluble vitamin (A, D, E, K) malabsorption
  • •GLP-1 agonists (semaglutide): CONTRAINDICATED with personal/FHx MTC or MEN 2

◆Disease-specific nutrition

  • •Metabolic syndrome: ≥3 of 5 (waist, TG ≥150, HDL <40/50, BP ≥130/85, FBG ≥100); first-line Mediterranean diet
  • •Heart failure: Na restriction (≤2 g); fluid restriction if Na <130
  • •CKD stages 4–5 (not on dialysis): protein 0.6–0.8 g/kg; once on dialysis 1.0–1.2 g/kg
  • •Cirrhosis: DO NOT restrict protein (1.2–1.5 g/kg) to prevent sarcopenia
  • •MASLD: 7–10% weight loss is most effective
  • •Kidney stones (calcium oxalate): INCREASE dietary calcium (binds oxalate in gut)
  • •Diabetes prevention: metformin if BMI ≥35, age <60, or prior GDM

◆Malnutrition assessment & PEM

  • •Albumin/prealbumin: NEGATIVE acute phase reactants — drop with inflammation; NOT reliable nutrition markers in acute illness
  • •Kwashiorkor: protein deficiency with adequate calories — bilateral pitting edema, distended abdomen, fatty liver
  • •Marasmus: total caloric + protein deprivation — wasting, no edema
  • •Frailty: ≥3 of 5 (weight loss, exhaustion, ↓grip strength, slow gait, low activity)
  • •Significant weight loss in LTC: ≥5% in 1 mo, ≥7.5% in 3 mo, ≥10% in 6 mo

High-yield pearls

  • ◆Thiamine before glucose in malnourished
  • ◆B12 before folate
  • ◆TPN + cardiomyopathy → Selenium; refractory hyperglycemia → Chromium
  • ◆Post-bariatric + posterior column signs + normal B12 + neutropenia = Copper deficiency
  • ◆Anorexia leading cause of death: cardiac arrhythmia
  • ◆Don't restrict protein in cirrhosis
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