The purpose of this study is to determine the effect of a prebiotic (BGOS) on gut microbiota and metabolites in children with autism spectrum disorders.

Children with ASD have a higher incidence of dietary and/or bowel problems than typically developing children. it has been postulated that imbalances in the gut bacteria and/or metabolites present in the gut may be a contributing factor to these symptoms, with potentially bad (toxin-producing) bacteria colonising the gut. Certain carbohydrates (so-called 'prebiotics') are not digested by the human gut and they provide food for beneficial bacteria and thus they improve the composition by preventing the growth of bad bacteria. Individuals could therefore benefit from these safe and effective dietary interventions to maintain the healthy gut bacteria and overall health. This study is being carried out to establish the effect of one such prebiotic, called galactooligosaccharide (B-GOS) on the relative balance of gut bacteria and metabolites in children with ASD. The aim is to enrol 42 children, ages 5-10 with formal ASD diagnosis and with signed informed consent from their parents, into double-blind, placebo controlled, parallel study. The trial will last 10 weeks in total (2 weeks run in period, 6 weeks treatment and 2 weeks follow up). Children will be required to take food supplement daily during the treatment period and their parents will collect stool, saliva and urine samples. Various questionnaires will also be used for assessments. Children will not be required to make other extra changes to their diet, medication or lifestyle.

Inclusion Criteria:

• children aged 5-10 years with formal ASD diagnosis
• children's parent or guardian has given written informed consent to participate and is willing to participate in the entire study

Exclusion Criteria:

• consumption of antibiotics, prebiotic or probiotics in the last 4 weeks prior to or during the study
• participants who have received bowel preparation for investigative procedures in the 4 weeks prior to the study
• undergone surgical resection of any part of the bowel

upon completion of the whole study, volunteers will be able to access their individual data following written request