Department of General Surgery, Jinling Hospital, Medical School of Nanjing University, Nanjing, China. Department of Medical Statistics, Jinling Hospital, Nanjing Medical University, Nanjing, China. Department of Biostatistics, School of Public Health, Southern Medical University, Guangzhou, China. Department of Hepatobiliary Pancreatic Surgery, Changhai Hospital, the Second Military Medical University, Shanghai, China. Department of General Surgery, First Affiliated Hospital of Kunming Medical University, Kunming, China. Department of Gastrointestinal Surgery, the Affiliated Hospital of Qingdao University, Qingdao, China. Department of General Surgery, the Second Affiliated Hospital of Harbin Medical University, Harbin, China. Department of General Surgery, the Second Affiliated Hospital, Army Medical University, Chongqing, China. Department of Gastrointestinal Surgery, the First Affiliated Hospital of Air Force Medical University, Xi'an, China. Department of General Surgery, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing, China. Department of General Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, China. Department of General Surgery, First Medical Center of Chinese PLA General Hospital, Beijing, China. Department of Gastrointestinal Surgery, West China Hospital, Sichuan University, Chengdu, China. Nutrition Unit, Geneva University Hospital, Lausanne, Switzerland.