MC, I tried to get to the bottom of why doctors might recommend limiting fats for gastritis. All I could find was one unconvincing publication on mutant (LDL receptor-negative (LDLR(-/-)) mice. http://www.ncbi.nlm.nih.gov/pubmed/11397709
Did your doctor happen to share any other information / publications with you supporting this idea?
Also, were you diagnosed with H. pylori and if so, was it treated successfully?