Nutrition, Malabsorption, and Obesity
Core concepts
Link malabsorption to the nutrient absorbed at each site. Fat malabsorption causes steatorrhea and fat-soluble vitamin deficiency; test with fecal fat or, practically, fecal elastase for pancreatic cause. B12 absorption requires intrinsic factor and ileum; deficiency causes macrocytic anemia and neurologic symptoms. Iron absorbs in duodenum; folate in jejunum. Celiac, bacterial overgrowth, and pancreatic insufficiency are common causes.
Obesity management progresses from lifestyle to pharmacotherapy to bariatric surgery. Know indications for surgery: BMI 40 or more, or 35 or more with comorbidities. Post-bariatric complications include dumping syndrome, micronutrient deficiencies (B12, iron, thiamine), and gallstones with rapid weight loss. Refeeding syndrome is dangerous: start slow and monitor phosphorus, potassium, and magnesium.
Traps
Do not treat B12 deficiency with oral B12 if pernicious anemia or ileal disease is present; use parenteral. Do not miss thiamine deficiency in malnourished patients before glucose loading. Do not attribute anemia in bariatric patients solely to iron; check B12 and folate.
Rule of thumb
In any severely malnourished patient, check and replete electrolytes, especially phosphorus, before aggressive feeding to prevent refeeding syndrome.