A 53-year-old man without remarkable medical or surgical history was evaluated for acute progressive macrocytic anemia (hemoglobin: 8.7 g/dL decreased from 10.3 two weeks ago, mean cell volume: 115.4 fL). The patient endorsed brown-colored, formed bowel movements without blood and denied unusual dietary habits, medication use or alcohol consumption. He reported his hair has been completely gray since his late-20s (Figure).