Fig 1.
Flowchart showing article selection.
Adapted from the PRISMA 2020 flow diagram [22].
Table 1.
General characteristics of the included randomised controlled trials.
Table 2.
Risk of bias of the included studies.
Table 3.
Effects of pre-, pro- or synbiotic interventions on microbiota composition.
Fig 2.
Bar charts showing the number of interventions (several studies used more than one intervention) with a significant effect on the microbiota composition at at least one time point in the clusters of 0–1 weeks (a), 1–4 weeks (b) or >4 weeks (c).