Objectives To assess evidence supporting the view that ‘low fibre causes childhood constipation’. Design Triangulation integrated three approaches: a systematic review NICE guideline CG99 examining effectiveness of increasing fibre; a cohort study, Avon Longitudinal Study of Parents and Children (ALSPAC), to assess if constipation (or hard stools) can precede fibre intake at weaning; and a literature search for twin studies to calculate heredity. Setting CG99 examined the literature regarding the effectiveness of increasing fibre. ALSPAC asked parents about: hard stools at 4 weeks, 6 months and 2.5 years and constipation at age 4–10 years, as well as fibre intake at 2 years. Twin studies and data from ALSPAC were pooled to calculate concordance of constipation comparing monozygotic and dizygous twin pairs. Participants CG99 reported six randomised controlled trials (RCTs). ALSPAC hard stool data from 6796 children at 4 weeks, 9828 at 6 months and 9452 at 2.5 years plus constipation data on 8401 at 4–10 years were compared with fibre intake at 2 years. Twin studies had 338 and 93 twin pairs and ALSPAC added a further 45. Results Increasing fibre did not effectively treat constipation. Hard stools at 4 weeks predated fibre and at 6 months predicted lower fibre intake at 2 years (p=0.003). Heredity explained 59% of constipation. Conclusions RCTs indicate that increasing fibre is not an effective treatment for constipation in children. Hard stools can precede and predict later fibre intake. Genetic inheritance explains most childhood constipation. Extended treatment with stool softeners may improve fibre intake and limit long-term damaging sequelae of constipation.
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