Carbohydrate and protein intake and risk of ulcerative colitis: Systematic review and dose-response meta-analysis of epidemiological studies

Background & aim: Dietary carbohydrate and protein intake is generally thought as risk factors for onset of ulcerative colitis (UC), while epidemiological data had been controversial. This study aimed to evaluate the role of carbohydrate and protein intake in the development of UC. Methods: Comprehensive search in PubMed and Embase was conducted to identify all relevant studies, and the role of carbohydrate and protein intake in the development of UC was quantitatively assessed by dose-response meta-analysis. Results: Nine studies (5 case-control and 4 prospective cohort) were identified with a total of 975 UC cases and 239352 controls. The summary relative risks (RR) for per 10 g increment/day were 1.005 (95% CI: 0.991-1.019, I-2 = 31.5%, n = 5) for total carbohydrate intake, 1.001 (95%CI: 0.971-1.032, I-2 = 0.0%, n = 7) for the subtype of fiber intake, 1.029 (95%CI: 0.962-1.101, I-2 = 68.9%, n = 2) for the subtype of sugar intake, and 1.010 (95%CI: 0.975-1.047, I-2 = 12.4%, n = 7) for total protein intake. Among sugar subtypes, only sucrose intake was found positively related with UC risk (RR for per 10 g increment/day: 1.098, 95%Cl: 1.024-1.177, I-2 = 0.0%, n = 3). No evidence of a non-linear dose-response association was found between the nutrient intake and UC risk, except for the subtype of sucrose (P for non-linear trend = 0.032). Subgroup analyses showed consistent results. Conclusions: This meta-analysis suggested a lack of association between dietary carbohydrate or protein intake and the risk of UC, except for the subtype of sucrose which played a significant role in the development of UC. Large-scale prospective designed studies are needed to confirm our findings. (C) 2016 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.