Nutrition, Obesity and Metabolic Complications
This domain tests nutritional assessment and support, the metabolic consequences of obesity and bariatric surgery, and the new nomenclature for fatty liver disease.
Nutritional assessment and support
- Screen with MUST or NRS-2002. Assess intake, weight trajectory, handgrip strength and biochemistry.
- Enteral nutrition is preferred whenever the gut works; parenteral nutrition is reserved for intestinal failure, obstruction, high-output fistula or severe malabsorption.
- Refeeding syndrome: hypophosphatemia, hypokalemia and hypomagnesemia after rapid refeeding in malnourished patients. Identify high risk (low BMI, minimal intake over 5 days or more, alcohol misuse), start at 10-20 kcal/kg/day, give thiamine before feeding, and monitor electrolytes daily.
- Short bowel syndrome: manage with fluid and electrolyte replacement, antisecretory drugs, and teduglutide in selected patients; the colon in continuity improves energy absorption.
Obesity and bariatric surgery
- BMI thresholds: 40 or more, or 35 or more with comorbidity; Asian guidelines use lower cut-offs (27.5 and 32.5).
- Sleeve gastrectomy and Roux-en-Y gastric bypass are most common. Bypass causes more malabsorption; sleeve is simpler but carries reflux and leak risk.
- Complications: dumping syndrome, anastomotic ulcer, internal hernia, thiamine deficiency (Wernicke encephalopathy), iron, vitamin B12, folate, and fat-soluble vitamin deficiency. Lifelong micronutrient supplementation and monitoring.
- GLP-1 receptor agonists cause delayed gastric emptying; consider holding before elective endoscopy or surgery per protocol.
Metabolic liver disease and complications of obesity
- Fatty liver nomenclature has moved to steatotic liver disease: MASLD (metabolic dysfunction-associated steatotic liver disease) requires steatosis plus at least one cardiometabolic criterion; MetALD describes combined metabolic and alcohol-related disease.
- Assess fibrosis with FIB-4 first, then elastography; lifestyle and weight loss of 7-10% remain central. Screen for type 2 diabetes, dyslipidemia and sleep apnea.
- Obesity is a risk factor for gallstones, pancreatitis, GERD and colorectal adenoma.
Worked example
A 34-year-old with a BMI of 41 and type 2 diabetes is admitted with vomiting 6 weeks after gastric bypass. Look for thiamine deficiency and give IV thiamine before glucose, because Wernicke encephalopathy can be precipitated by carbohydrate loading.
Traps
- Starting full-calorie feeding in a severely malnourished patient.
- Forgetting thiamine before glucose in the malnourished patient.
- Assuming a normal BMI excludes malnutrition.
- Missing micronutrient deficiency years after bariatric surgery.