Yellow stool is typically due to an excess of fatty foods and grease in the diet. Mayo Clinic states that it can also be caused by a malabsorption disorder such as celiac disease.
Yellow stool is generally a sign that food has passed through the digestive tract too quickly. Because bile salts from the liver give stool its brown color, yellow stool can indicate abnormalities with the gallbladder and liver. Healthgrades states that it can also be caused by an infection such as giardiasis. Giardia is a parasite found in waste and contaminated water that causes yellow diarrhea accompanied with flu-like symptoms.