Abstract
Inulin is a soluble dietary fibre, also classified as a prebiotic, extracted from chicory roots. The present study aimed to determine the effect of consumption of native chicory inulin on the stool frequency of middle-aged to older adults (40–75 years old) with uncomfortably but not clinically relevant low stool frequency, specified as two to four days without bowel movements per week. Two randomised, double blind, placebo-controlled crossover trials were conducted using similar protocols in differing populations. Trial A was conducted in Amsterdam, The Netherlands and subsequently Trial B was conducted in Newcastle, United Kingdom. Both trials involved supplementation for 5 weeks with 10 g per day of inulin or placebo, a washout period of 2 weeks, and then crossed over to receive the other treatment. In Trial B, faecal gut microbiota composition was assessed using 16S rRNA gene sequencing. In Trial A, which 10 volunteers completed, the stool frequency was significantly increased to an average 4.9 ± 0.23 (SEM) times per week during inulin periods versus 3.6 ± 0.25 in the periods with placebo (p = 0.01). In contrast, in Trial B which 20 volunteers completed, there was no significant effect of the inulin on stool frequency (7.5 ± 2.1 times per week with inulin, 8.1 ± 3.0 with placebo, p = 0.35). However, many subjects in Trial B had a stool frequency >5 per week also for the placebo period, in breach of the inclusion criteria. Combining the data of 16 low stool frequency subjects from Trials A and B showed a significant effect of inulin to increase stool frequency from 4.1 to 5.0 per week (p = 0.032). Regarding secondary outcomes, stool consistency was significantly softer with inulin treatment compared to placebo periods, it increased 0.29 on the Bristol stool scale (p = 0.008) when data from all subjects of Trials A and B were combined. No other differences in bowel habit parameters due to inulin consumption were significant. None of the differences in specific bacterial abundance, alpha or beta diversity were significant, however the trends were in directions consistent with published studies on other types of inulin. We conclude that 10 g per day of native chicory inulin can increase stool frequency in subjects with low stool frequency.
Highlights
Constipation is a gastrointestinal tract (GIT) symptom that is characterised by irregular, difficult and/or painful stool expulsion and hard, dry stool consistency (Mccrea et al, 2009), and can cause additional GIT symptoms such as distention, abdominal pain and poor appetite, amongst others (Lembo & Camilleri, 2003)
There was a significant increase in stool frequency at week 5 (p = 0.04) and for the average trial score (p = 0.01). These changes correspond to an increase in frequency of 1.3 bowel movements per week; bowel movements increased from an average ± standard error of mean (SEM) of 3.6 ± 0.25 to 4.9 ± 0.23 per week (Fig. 3a)
Time point and treatment period were not significantly associated with the microbiota profiles (p = 0.920) and (p = 0.922), respectively, explaining only 0.3% and 0.1% of the overall variability, respectively. This corroborates the previous findings that each volunteer has a unique bacterial community, which is stable over time despite inulin intervention. These randomised, double blind, placebo-controlled trials assessed the effects of inulin on bowel symptoms of constipation, with stool frequency as the primary outcome, quality of life and gut microbiota composition in middle-aged to elderly populations
Summary
Constipation is a gastrointestinal tract (GIT) symptom that is characterised by irregular, difficult and/or painful stool expulsion and hard, dry stool consistency (Mccrea et al, 2009), and can cause additional GIT symptoms such as distention, abdominal pain and poor appetite, amongst others (Lembo & Camilleri, 2003). The prevalence of constipation is difficult to determine as most people do not seek medical treatment, it is estimated to cause recognised discomfort to around 2–27% of the general population, with an increase with age (Gallagher & O'mahony, 2009). Consuming less than the recommended daily fibre intake of 25 g/day has been associated with an increased incidence of constipation (Suares & Ford, 2011). In a recent meta-analysis, increased dietary fibre has been shown to be a useful treatment in those people suffering with constipation (Rao, Yu, & Fedewa, 2015), how to increase dietary fibre intake remains an area of concern, and it is not known if all types of fibres have equal effects
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