Table 1.

Terms and definitions of functional constipation, prebiotics and dietary fibre

Terms and definitions
Functional constipation	Functional constipation, normal and slow transit constipation, chronic or chronic idiopathic constipation are used interchangeably(14,69). Here the definition according to the ROME foundation’s expert committee of gastroenterologists is used, with the Rome IV criteria being current at the time of writing(3). A person must have experienced at least two of the following symptoms for the previous 3 months to be diagnosed with functional constipation: Fewer than three spontaneous bowel movements per week; straining for more than 25 % of defecation attempts; lumpy or hard stools for at least 25 % of defecation attempts; sensation of anorectal obstruction or blockage for at least 25 % of defecation attempts; sensation of incomplete defecation for at least 25 % of defecation attempts; manual manoeuvring required to defecate for at least 25 % of defecation attempts. In addition, loose stools should rarely be present without laxatives and there should be no diagnosis of irritable bowel syndrome (IBS).
Prebiotics	In 2016, the International Scientific Association for Probiotics and Prebiotics defined prebiotics as substances which are selectively used by microbes conferring a demonstrated health benefit to the host(70). They are mainly non-digestible oligosaccharides fructans, galactans and inulin(71). They may include polyphenols and conjugated fatty acids. Candidate prebiotics include pectins, arabinoxylan, resistant starches, whole grains, cellulose, mannose, maltose, polydextrose, lactulose and β-glucans(71).
Dietary fibre	Natural foods contain a mix of soluble and insoluble fibres. Soluble fibres can be viscous (psyllium) or non-viscous (guar gum), and in addition fermentable (guar gum, pectins, inulin) or non-fermentable (cellulose, lignin) with overlapping categories(72). Only fermentable fibre has an effect on microbiota but not necessarily an effect on laxation(70).