Gallbladder removed two months ago. some fatty foods will cause bright yellow diarrhea right after. why? is this normal?

Yes.: The gallbladder serves as a storage place for bile made in the liver. Bile helps us digest fatty food. After the gallbladder is removed, the body has to adjust to a new system where the bile comes directly from the liver. Some patients take longer to adjust and may have fatty food intolerance. If the fat isn't getting absorbed, it passes through into the stool (technically called steatorrhea).

Gallbladder/Diarrhea: Some patient after having gallbladder surgery will have postprandial diarrhea. This is likely related to bile overflow since your gallbladder is removed and now bile is being stored in the duodenum (could lead to overproduction). Aka post-cholecystic syndrome. Majority of patients will have symptoms resolved within 3 months. If not, can use Cholestyramine to control the diarrhea.