Objective To analyze the impact of body mass index (BMI) on surgical difficulty and surgical reaction of patients with colorectal cancer served by West China Hospital, based on the current version of Database from Colorectal Cancer (DACCA). MethodsThe data of DACCA were updated on September 22, 2021. All data items included BMI, operative duration, anatomical difficulty, pelvic stenosis, abdominal obesity, adhesion in surgical area, abnormal mesenteric status, tissue or organ hypertrophy, intestinal quality in surgical area, surgery reaction, and perioperative complications of colorectal cancer module including temperature, flatus, pain, and mental status. The patients were divided into lean (BMI <18.5 kg/m2), normal (BMI 18.5–23.9 kg/m2), overweight (BMI 24.0–27.9 kg/m2), and obesity (BMI ≥28.0 kg/m2) by Chinese four classification method. ResultsAfter scanning, 6 311 data rows were analyzed. ① The effect of BMI on surgical difficulty: BMI was weakly positively correlated with operative duration (rs=0.096, P<0.001). The overweight and obesity patients were more likely to have anatomical abnormalities (rs=0.385, P<0.001 ), pelvic stenosis (rs=0.386, P<0.001), abdominal obesity (rs=0.567, P<0.001), and adhesion in surgical area (rs=0.043, P=0.004). There was difference in tissue or organ hypertrophy among patients with different BMI (χ2=39.988, P<0.001). It was also found that the lean patients were prone to develop ‘very heavy adhesions’ when adhesions occurred in surgical area, and to ‘mesangial contracture, short, fixed’ of abnormal mesenteric status, while the obesity patients were prone to ‘mesangial thickening’ of abnormal mesenteric status. There was no difference in intestinal quality among patients with different BMI (P>0.05). ② The effect of BMI on surgical reaction: BMI was weakly positively correlated with the overall assessment of surgical reaction (rs=0.049, P=0.001), and obesity patients were more likely to have severe surgical reaction. BMI was weakly negatively correlated with pain (rs=–0.058, P<0.001）and the lean patients were more likely to have pain that needed drug control. However, there were no differences in temperature, flatus, and mental status among patients with different BMI (P>0.05). ConclusionsHigh BMI of patients will affect several indicators including operative duration, anatomical difficulty, pelvic stenosis, abdominal obesity, adhesion in surgical area, abnormal mesenteric status, tissue or organ hypertrophy, resulting in increased difficulty of surgery. Although high BMI might affect overall response state after surgery, it will not affect temperature, flatus, and mental status, reflecting a relatively weak impact on surgical reaction.