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261 Pre-, pro- and synbiotics 12 microbiota in healthy Dutch children between 2–18 years, specifically excluding children with FC. 30 Analysis of fecal samples revealed that microbial compositional stability was 70% on average over a period of 18 months, indicating that a fairly stable core gut microbiota is likely to exist within the gut of healthy children. Also, microbiota stability correlated with higher microbial diversity. The core gut microbiota of these children was dominated by species from the phyla Bacteroidetes and Firmicutes. Aside from the study by Zhu  et al.  in obese children 2 , there are no studies that have used culture-independent techniques to assess the microbiota of children with FC. This study found differences between constipated and non-constipated obese children with regard to microbiota composition and diversity. A significantly decreased abundance of Prevotella and an increased representation of several genera of Firmicutes were observed in constipated patients compared with controls. 2 Interestingly, the genera that have been used in most probiotic trials so far ( Bifidobacterium  and  Lactobacillus , from the phyla Actinobacteria and Firmicutes respectively) were not decreased in constipated patients. This may possibly explain the negative outcomes of the probiotic trials as discussed in this systematic review. Furthermore, Zhu  et al.  demonstrated a lower gut microbiota diversity in children with FC. 2 Microbiota diversity has been shown to be decreased in a number of gastrointestinal and non-gastrointestinal diseases and it has been hypothesized that regaining microbial diversity may potentially be beneficial. 1,31 In support of this hypothesis, a recent pilot study of fecal microbiota transplantation in adults with FC has shown promising results. 32 Future studies are needed to further investigate the role of the gut microbiota in children with FC and to further evaluate the role of microbial diversity in the pathogenesis. Also, a better understanding of the role of specific pre- and probiotics in the process of defecation is warranted. This will result in a more tailored approach in using pre- and probiotics in the treatment of FC. In conclusion, there is insufficient evidence to recommend pre-, pro- or synbiotics in the treatment of children with FC. A better understanding of the gut microbiota in healthy and constipated children is needed. Furthermore, large, high-quality randomized controlled trials are warranted.