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336 In chapter 2 , we describe a cross-sectional population-based study on the association between overweight and FC in 2,820 Colombian children. A Spanish translation of the QPGS-RIII was used to diagnose FC, while anthropometric data on weight, height, and body mass index were obtained following World Health Organization (WHO) guidelines. In this study, 13.0% of children fulfilled the Rome III criteria for FC, 19.2% were overweight and 6.7% were obese. We did not find FC to be more prevalent in children who were obese or overweight compared to children with a normal weight. Interestingly, FC and excessive bodyweight were found to be significantly more prevalent in children attending private schools compared with children attending public schools. We hypothesized that this difference could be related to lifestyle factors associated with higher socioeconomic status. The results from our study, performed in a developing country, did not confirm findings from previously published studies performed in developed countries which had demonstrated an association between FC and excessive bodyweight in children. 9–13 This led to the hypothesis that factors such as genetics, lifestyle, diet and socioeconomic status could play an important role in the association between FC and overweight. In addition, we emphasized that, unlike our own study, most studies demonstrating an association between FC and excessive bodyweight had been performed in hospital settings. We concluded that it would be valuable to investigate the different factors that could explain the differences found between our study and previous studies. Therefore, in chapter 3 , we conducted a systematic review of the literature assessing the association between FDDs and excessive bodyweight. For this systematic review, we included eight studies; two studies evaluated the prevalence of FDDs in obese children, three studies evaluated the prevalence of overweight or obesity in children with FDDs, and three studies evaluated the association between FDDs and bodyweight in a population-based sample. An association between FDDs and excessive bodyweight was reported in both studies conducted in obese children and in two out of three studies in children with FDDs. However, results from larger population-based studies were less convincing; only one out of three studies reported a significant association. Since study results varied strongly across included studies, we could neither confirm nor refute an association between FDDs and excessive bodyweight in children based on the available data. In chapter 4 we evaluated the association between attention deficit hyperactivity disorder (ADHD) and FDDs. We asked parents of children with FDDs to complete the Child Behavior Checklist (CBCL) and the VvGK (a Dutch questionnaire based on the American Disruptive Behavior Disorder rating scale). Children with CBCL or VvGK scores suggestive for ADHD were referred for psychiatric evaluation. Moreover, we asked parents of children treated for ADHD at a specialized ADHD outpatient clinic to complete a standardized questionnaire regarding their child's defecation pattern to assess if their child fulfilled the Rome III criteria for FDDs. Out of 282 children with FDDs, 10.3% had ADHD and out of 198 children seen