15 · Nutrition & Metabolic Disorders

Vitamins, deficiencies, refeeding, obesity, food sensitivities, and the classic metabolic diseases.

Nutrition blueprint: hypo/hypervitaminosis, malabsorption, refeeding syndrome, obesity/metabolic syndrome, food allergies/sensitivities, and metabolic disorders.

Vitamin deficiencies (high-yield)

Vitamin	Deficiency
A	Night blindness, xerophthalmia, Bitot spots
B1 (thiamine)	Wernicke-Korsakoff (alcoholics; give thiamine BEFORE glucose), wet/dry beriberi
B3 (niacin)	Pellagra — diarrhea, dermatitis, dementia
B9 (folate)	Megaloblastic anemia; neural tube defects (supplement preconception)
B12	Megaloblastic anemia + neurologic (subacute combined degeneration); pernicious anemia, terminal-ileum disease, vegans
C	Scurvy — bleeding gums, perifollicular hemorrhage, poor healing
D	Rickets (children) / osteomalacia (adults)
E	Neuropathy, hemolysis (ataxia)
K	Bleeding / elevated PT (newborns get IM vitamin K)

⭐ Fat-soluble vitamins (A, D, E, K) are malabsorbed in fat malabsorption (celiac, pancreatic insufficiency, cholestasis). In an alcoholic, give thiamine before glucose to prevent precipitating Wernicke encephalopathy.

Refeeding, obesity & food sensitivities

Topic	Key points
Refeeding syndrome	Reintroducing carbohydrates in a malnourished patient → insulin surge drives electrolytes intracellularly → hypophosphatemia (also hypokalemia, hypomagnesemia) → arrhythmia; refeed slowly, replete phosphate/K/Mg + thiamine, monitor.
Obesity & metabolic syndrome	BMI ≥30 obese; metabolic syndrome = 3 of 5: central obesity, ↑triglycerides, ↓HDL, hypertension, hyperglycemia; lifestyle first, then pharmacotherapy/bariatric surgery.
Lactose intolerance	Bloating/diarrhea after dairy; lactase deficiency; avoid lactose or use enzyme.
Food allergy (IgE)	Milk, egg, peanut, tree nut, soy, wheat, fish, shellfish; anaphylaxis risk → epinephrine + avoidance.
Malnutrition markers	Albumin (chronic, t½ ~20 d) vs prealbumin (acute, t½ ~2 d); both fall with inflammation.

Metabolic disorders

Phenylketonuria (PKU): phenylalanine hydroxylase deficiency; newborn screen; untreated → intellectual disability, "musty" odor, eczema; phenylalanine-restricted diet (avoid aspartame).
Rickets: vitamin D deficiency → bowed legs, growth-plate widening, ↓Ca/phosphate; supplement vitamin D/calcium.
Also seen: galactosemia, glycogen storage diseases, urea-cycle defects (part of newborn metabolic screening).