Elemental diets are effective treatments for active Crohn's disease. To determine which dietary constituents are of therapeutic importance, the effectiveness of four separate feeds was related to their compositions, and the findings substantiated by meta-analysis of previous dietary studies. 76 patients with active Crohn's disease were recruited. 17 were randomised to an amino acid-based elemental diet (E028), 22 to E028 with added long-chain triglyceride (E028 LCT), 18 to a semi-elemental, peptide based diet (Pepdite 2+) and 19 received E028 with added medium-chain triglyceride (E028 MCT). Disease activity fell in all groups and remission rate was negatively correlated with the amount of energy derived from LCT (r = -0.97, p = 0.016). Inflammatory indices fell in the groups (E028 + E028 MCT) containing least LCT. No other dietary constituents correlated with remission rate. A meta-analysis of published studies confirmed a negative correlation between remission rate and LCT (r = -0.63, p = 0.006) but not other constituents. The association between dietary LCT and remission rate may have pathogenic significance and allow the development of more effective enteral feeds.