The Impact of Dietary Fiber Supplementation on Gut-Brain Axis Biomarkers and Symptoms in Functional Constipation: A Meta-Analysis of Randomized Controlled Trials.

In adults with chronic idiopathic constipation, the AGA-ACG panel suggests the use of fiber supplementation over management without fiber supplementation. This is a CONDITIONAL recommendation based on LOW certainty of evidence. The guideline attaches several qualifiers that must not be dropped: (1) among the fiber supplements the panel evaluated, psyllium (3 trials), bran (1 trial), inulin (2 trials), methylcellulose (no trials found), only psyllium appears to be effective, with 'very limited and uncertain' data on bran and inulin and no evidence base at all for methylcellulose; (2) there is no clear evidence that soluble or insoluble fiber is more effective for constipation specifically; (3) on implementation, 'fiber supplements can be used as first-line therapy for CIC, particularly for individuals with low dietary fiber intake,' and 'dietary assessment is important to determine total fiber intake from diet and supplements'; (4) 'a trial of fiber supplement can be considered for mild constipation before PEG use or in combination with PEG'; (5) the total daily fiber target cited by the guideline is 20-30 g/day from diet plus supplement, derived from the Academy of Nutrition and Dietetics figure of 14 g per 1,000 kcal; (6) flatulence is a commonly observed side effect and adequate hydration should be encouraged. Fiber's placement within the guideline's own hierarchy is itself part of the recommendation: polyethylene glycol, bisacodyl, sodium picosulfate, linaclotide, plecanatide and prucalopride carry STRONG recommendations, whereas fiber, magnesium oxide, lactulose, senna and lubiprostone carry CONDITIONAL ones.