Biliary Colic or Cholecystitis: Pain after a fatty meal is a classic symptom of gallbladder pathology, as fatty foods trigger the release of cholecystokinin, which can cause the gallbladder to contract. If the gallbladder is inflamed or if there are gallstones, this contraction can cause pain.

Pancreatitis: While pancreatitis more commonly presents with mid-abdominal pain radiating to the back, it can sometimes cause left flank pain, especially if the pancreatic tail is involved. A fatty meal can trigger pancreatitis in susceptible individuals.
Gastroesophageal Reflux Disease (GERD): Although GERD typically presents with heartburn and regurgitation, it can sometimes cause chest or abdominal pain that might be referred to the left flank, especially after eating fatty or large meals.
Diverticulitis: Inflammation of the diverticula in the sigmoid colon, which is located in the left lower quadrant, can cause left flank pain. While not directly related to fatty meals, diverticulitis can cause pain that worsens after eating.

Kidney Stone: Although kidney stones are more commonly associated with severe, colicky pain, they can sometimes present with more dull, persistent pain. A stone in the left ureter could cause left flank pain, and while not directly related to eating, the pain could potentially worsen after increased fluid intake, which might occur with meals.
Appendicitis: While appendicitis typically presents with right lower quadrant pain, a retrocecal appendix can cause pain that is more diffuse or even on the left side. It's crucial to consider appendicitis in any case of abdominal pain, as it requires prompt surgical intervention.
Aortic Dissection: This is a life-threatening condition where there is a tear in the aorta's inner layer. It can cause severe, tearing pain that can be in the abdomen, back, or flank, and is not directly related to eating but is crucial to diagnose quickly.

Splenic Infarction: This can cause severe left upper quadrant or flank pain and is more likely in individuals with sickle cell disease, blood clots, or other conditions affecting the spleen.
Left Ovarian Pathology: Conditions like ovarian torsion or cyst rupture can cause severe left flank pain in women, though these are not typically associated with eating fatty meals.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause chronic abdominal pain, including left flank pain, though the pain is usually not directly triggered by fatty meals.