Fructooligosaccharides for Relieving Functional Constipation: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Abstract

Fructooligosaccharides (FOS) are prebiotics with great potential to improve constipation. This study set out to investigate the usefulness of consuming FOS as a dietary supplement on bowel movement frequency, stool consistency, abundance of Bifidobacteria, gastrointestinal transit time, and gastrointestinal symptoms through a systematic review and meta-analysis of randomized controlled trials (RCTs). We searched the Cochrane Library, PubMed, EMBASE, and Web of Science databases up to 2 March 2024. Randomized controlled trials reporting the use of FOS as a supplement by participants were included. Bias risk was assessed using the Cochrane Risk of Bias assessment tool. Results were synthesized using a random-effects model or fixed-effects model, combining outcomes using odds ratios (OR), weighted mean differences (MD), or standardized mean differences (SMD) with 95% confidence intervals (CI). The meta-analysis encompassed 17 randomized controlled trials, involving a total of 713 study participants. Overall, the intake of FOS significantly increased bowel movement frequency (95% CI: 0.80, 1.50, p < 0.00001) and positively affected stool consistency, softening the stool (SMD: 0.36, 95% CI: 0.12, 0.60, p = 0.76). It also reduced the effort and pain during defecation (SMD: -0.60, 95% CI: -0.85, -0.34, p = 0.12). At the same time, mild bloating was noted as an adverse event associated with FOS ingestion (OR: 10.36, 95% CI: 3.32, 33.23, p = 0.24). No reports of serious adverse events were documented. Overall, FOS may enhance bowel movement frequency, stool consistency, and overall constipation symptoms, suggesting cautious optimism regarding their use as a dietary treatment alternative. Nevertheless, further robust and definitive randomized controlled trials are required to more accurately determine the most effective dosage and duration of use. Additional research and evidence are necessary before the efficacy of FOS as a therapeutic method for treating functional constipation can be firmly established.

Keywords: constipation; fructooligosaccharides (FOS); gut microbiota; meta-analysis.

Figure 1

PRISMA Flowchart of study selection.

Figure 2

Forest plot for the effect of FOS on stool frequency [21,22,23,25,26,28,29,30,31,32,33,34,35].

Figure 3

Subgroup analysis of stool frequency after FOS intake based on health status [21,22,23,25,26,28,29,30,31,32,33,34,35].

Figure 4

Forest plot for the effect of FOS on stool consistency [21,31,32,33,34].

Figure 5

Forest plot for the effect of FOS on straining effort and pain [21,26,28,29].

Figure 6

Forest plot for the effect of FOS on abdominal distension [25,26,31,35,37].

Figure 7

Risk of bias graph: the judgements about each risk of bias item presented as percentages across all included studies.

Figure 8

Risk of bias summary: the judgements about each risk of bias item for each included study [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37].

Figure 9

Putative, microbe-driven mechanisms for FOS action and the functional roles of SCFAs. FOS is fully transported and hydrolyzed by cytoplasmic GH32 family β-fructofuranosidase. The extracellular hydrolysis of FOS is mediated by surface-associated GH32 β-fructofuranosidase, followed by the uptake of hydrolysis products through one or more transport proteins. SCFAs are rapidly absorbed by colonic cells via monocarboxylate transporters, passive diffusion, or an exchange mechanism with bicarbonate (HCO₃⁻), subsequently undergoing partial oxidation to carbon dioxide (CO₂) to generate ATP for cellular energy. SCFAs can enhance intestinal motility by activating receptors that promote the production of 5-hydroxytryptamine (5-HT), leading to increased synthesis and release of 5-HT. Additionally, SCFAs can activate GPR-43 and GPR-41 receptors, resulting in the production of gut peptides such as GLP-1 and PYY, which enhance pancreatic sensitivity to insulin. SCFAs exhibit antioxidant activity, reducing intracellular oxidative stress and protecting cells from oxidative damage, thereby mitigating β-cell injury and promoting insulin secretion. By decreasing oxidative stress, SCFAs also help maintain the activity of glutathione S-transferase (GST), thereby enhancing its capacity to effectively eliminate harmful substances.