Which nutrients are most commonly deficient after Roux-en-Y gastric bypass?

• A. Vitamin C and potassium
• B. Iron and zinc only
• C. Iron, B12, vit D, calcium, and thiamine
• D. Folic acid and magnesium only

Answer: (C)

After Roux-en-Y gastric bypass, the rearranged anatomy reduces stomach acid and bypasses portions of the small intestine, leading to malabsorption of several key nutrients. Iron deficiency is common because absorption largely happens in the duodenum and needs an acidic environment, both of which are diminished after the procedure. Vitamin B12 deficiency is also frequent since its absorption relies on intrinsic factor produced by the stomach and passage through the stomach to the ileum; the smaller stomach and altered digestion reduce B12 uptake. Calcium and vitamin D are often low as fat malabsorption and reduced stomach function impair calcium absorption and vitamin D status, which together threaten bone health. Thiamine (vitamin B1) deficiency can occur early postoperatively with poor intake or vomiting, risking serious neurologic issues if not addressed. These nutrients are the ones most routinely monitored and supplemented after this surgery, making them the best answer. Other options mention nutrients that are less consistently deficient or are addressed more variably in practice, so they don’t capture the typical post-op pattern as effectively.