A 4-month-old boy is brought to the physician by his parents for a well-child examination. He has cystic fibrosis diagnosed by newborn screening. His parents report frequent feedings and large-volume and greasy stools. His 4-year-old brother has autism. Current medications include bronchodilators, pancreatic enzyme supplements, and fat-soluble vitamins. He is at the 18th percentile for height and 15th percentile for weight. Scattered wheezes are heard throughout both lung fields. Examination shows a distended and tympanic abdomen with no tenderness or guarding. Which of the following is a contraindication for administering one or more routine vaccinations?

Fever of 38.2°C (100.7°F) following previous vaccinations

An 11-month-old boy is brought to a pediatrician by his parents for evaluation of vomiting and watery diarrhea over the last day. The mother informs the pediatrician that the boy had consumed an apple bought from a fruit vendor on the previous day, but that otherwise there has been no recent change in his diet. There is no history of blood in the stool, flatulence, irritability, or poor appetite. There is no history of recurrent or chronic diarrhea or any other gastrointestinal symptoms. On physical examination, his temperature is 37.6°C (99.6°F), pulse is 120/min, respirations are 24/min, and blood pressure is 92/60 mm Hg. General examination reveals a playful infant with normal skin turgor and no sunken eyes. The pediatrician explains to the parents that he most likely has acute gastroenteritis and that no specific medication is indicated at present. He also instructs the parents about his diet during the illness and reviews the danger signs of dehydration. He suggests a follow-up evaluation after 48 hours or earlier if any complications arise. Which of the following dietary recommendations did the pediatrician make?

Plenty of juices and carbonated sodas

A 31-year-old woman comes to the emergency department because of a 4-day history of fever and diarrhea. She has abdominal cramps and frequent bowel movements of small quantities of stool with blood and mucus. She has had multiple similar episodes over the past 8 months. Her temperature is 38.1°C (100.6°F), pulse is 75/min, and blood pressure is 130/80 mm Hg. Bowel sounds are normal. The abdomen is soft. There is tenderness to palpation in the left lower quadrant with guarding and no rebound. She receives appropriate treatment and recovers. Two weeks later, colonoscopy shows polypoid growths flanked by linear ulcers. A colonic biopsy specimen shows mucosal edema with distorted crypts and inflammatory cells in the lamina propria. Which of the following is the most appropriate recommendation for this patient?

Start annual colonoscopy starting in 8 years

Obtain barium follow-through radiography in 1 year

Obtain glutamate dehydrogenase antigen immunoassay now

Start annual magnetic resonance cholangiopancreatography screening in 10 years

A 17-year-old girl is brought in by her mother due to rapid weight loss over the past month. The patient says she has been having episodes of diarrhea, which she attributes to laxatives she takes regularly to keep her weight down. She also says she has not had her period yet. The patient’s mother adds that the patient has been underperforming at school and acting very strangely at home. Her current BMI is 16.8 kg/m2. On physical examination, the skin on her limbs and around her neck is inflamed and erythematous. Her tongue is bright red and smooth. She states that over the last 2 weeks, she has been eating nothing but small portions of fruit. She is diagnosed with a vitamin deficiency. Which of the following statements is true about the vitamin most likely deficient in this patient?

Synthesis requires vitamin B2 and B6

It increases the GI absorption of iron

Synthesis requires vitamin B1 and B6

It is used to treat hypertension

Nutritional considerations in IBD for USMLE Step 1: High-Yield Internal Medicine Lessons

Pathophysiology - The Gut's Uphill Battle

Chronic Inflammation: The primary driver, causing mucosal damage and systemic catabolism.
- Malabsorption: Reduced absorptive surface area from ulceration and villous atrophy. Specific sites matter (e.g., terminal ileum in Crohn's).
- Increased Gut Permeability: "Leaky gut" allows translocation of bacterial products, fueling inflammation.
Increased Energy Expenditure:
- Systemic inflammation (↑ cytokines) and fever raise the basal metabolic rate.
- Protein-losing enteropathy from inflamed mucosa.
Decreased Oral Intake:
- Anorexia, nausea, abdominal pain, and fear of eating (sitophobia).

⭐ Crohn's disease of the terminal ileum classically impairs the absorption of Vitamin B12 and bile salts, leading to megaloblastic anemia and fat-soluble vitamin deficiencies.

Micronutrient Deficiencies - The Nutrient Lineup

IBD disrupts nutrient absorption, leading to key deficiencies.

Iron: Most common deficiency. Caused by chronic blood loss and inflammation (anemia of chronic disease).
Vitamin B12: Classic in Crohn's disease due to terminal ileitis or resection.
Folate: Malabsorption; also impaired by medications like sulfasalazine and methotrexate.
Fat-Soluble Vitamins (A, D, E, K): Bile salt malabsorption in ileal disease impairs absorption.
- Vitamin D & Calcium: Risk of osteoporosis is high, exacerbated by corticosteroid use. Monitor bone density.
Zinc: Lost through diarrhea and fistulas; essential for mucosal healing.
Selenium: Reduced levels due to inflammation and poor intake.

Nutrient absorption sites in the GI tract

⭐ Always suspect Vitamin B12 deficiency in a Crohn's patient with megaloblastic anemia and neurological symptoms, especially with a history of ileal resection.

Dietary Therapy - Food as Pharmacy

Goal: Induce/maintain remission, correct nutritional deficiencies, & manage symptoms (e.g., bloating, pain).
Exclusive Enteral Nutrition (EEN):
- First-line induction therapy in pediatric & adult Crohn's Disease.
- Provides 100% of caloric needs as a liquid formula for 6-8 weeks.
Symptom-Targeted Diets:
- Low-FODMAP: For functional symptoms like gas & bloating.
- Low-Residue/Fiber: For patients with strictures to minimize obstruction risk.

⭐ Exclusive Enteral Nutrition (EEN) is as effective as corticosteroids for inducing remission in Crohn's disease, with superior mucosal healing and an improved safety profile, especially in children.

Emerging Therapies: Crohn's Disease Exclusion Diet (CDED) and Specific Carbohydrate Diet (SCD) are being studied as maintenance options.

Nutritional Support - Pipeline Power

Enteral Nutrition (EN): Preferred "gut-first" route for moderate-severe disease or malnutrition. Polymeric formulas are standard.
- Aims to correct deficits, support healing, and can be a primary therapy to induce remission (especially in pediatric Crohn's).
Parenteral Nutrition (PN): Used only when the GI tract is non-functional.
- Indications: Complete bowel obstruction, high-output fistulas, severe short bowel syndrome.
- ⚠️ Higher risk of line sepsis, cholestasis, and metabolic issues.

⭐ Exclusive Enteral Nutrition (EEN) is a first-line therapy for inducing remission in pediatric Crohn's disease, rivaling corticosteroids with a better safety profile and promoting superior mucosal healing.

High-Yield Points - ⚡ Biggest Takeaways

Malnutrition is a universal concern in IBD, stemming from poor intake, malabsorption, and inflammation-driven catabolism.

Enteral nutrition can induce remission in Crohn's disease, particularly in pediatric patients; less effective in UC.

Total Parenteral Nutrition (TPN) is reserved for severe disease, obstruction, or short bowel syndrome.

Routinely screen for deficiencies, especially iron, B12, vitamin D, and zinc.

Folic acid supplementation is crucial with sulfasalazine or methotrexate use.

Low-residue/low-fiber diets are for symptom control during active flares only.

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