Signs related to chronic gastrointestinal (GI) disease, such as occasional vomiting, are so common in the cats that the exact number of cats affected is unknown and likely underestimated. As many owners consider the signs “normal,” cats commonly present to veterinarians in advanced stages of disease, when nutritional deficiencies and impact on quality of life develop. Cats with intestinal (GI) disease have low blood iron levels and low vitamin B12. Inflammation in the body caused by the GI disease can trap iron in cells, preventing its movement throughout the body. Cats with decreased appetites may also take in less iron through their diets and may have decreased absorption of dietary iron due to disease in the intestines. As iron is needed for the formation of red blood cells, this can result in decreased red blood cell formation. Low vitamin B12 levels decrease the body’s ability to form red blood cells and cause structural changes within the intestines that decrease nutrient absorption, including iron. In people, low iron is associated with worse signs of GI disease, but this has not been studied in cats specifically with GI disease. If our study shows that cats with iron deficiency have a decreased response to standard-of-care treatment for GI disease, results would expand treatment options for cats affected by long-standing GI disease.