Fiber blend relieves constipation and improves stool consistency

By Dr. Liji Thomas, MDReviewed by Lauren HardakerJun 30 2026

Adults with chronic functional constipation experienced more frequent bowel movements and better stool consistency after taking a blend of dietary fibers from multiple food sources in a placebo-controlled trial.

Study: Combination of Dietary Fibers From Different Food Origins as a Treatment for Adults With Functional Constipation: A Randomized Clinical Trial. Image credit: triocean/Shutterstock.com

A recent study in the journal Food Science & Nutrition reports that a combination of dietary fibers from various foods significantly improved symptoms of functional constipation in a small randomized clinical trial compared with placebo.

Chronic constipation remains difficult to treat 

Constipation may present as fewer than three bowel movements per week, or as irregular bowel movements, hard or lumpy stools, having to strain excessively during defecation, or a feeling of incomplete evacuation. Chronic constipation, lasting for three or more months, is reported in up to 15% of the population. It reduces quality of life, accounts for a significant share of healthcare spending, and is often difficult to treat.

One common cause of chronic constipation is functional constipation. Adequate hydration and the inclusion of whole grains, legumes, vegetables, and fruits in the diet are the primary treatment strategies for constipation. These are valuable sources of dietary fiber that pass down into the colon. There, fiber is either fermented by gut microbes to produce beneficial bioactive compounds, or absorbs water to increase stool bulk. Insoluble fiber, if present, mechanically triggers mucus secretion by the intestinal mucosa, increasing motility.

However, most people consume too few vegetables. Earlier studies suggest that, in the short term, increasing vegetable intake is associated with increased abdominal gas, distension, and bloating, thereby promoting the use of laxatives.

However, laxatives do not provide uniform relief. The overall lack of effective and well-tolerated treatments motivated the current study, a small, single-center randomized clinical trial that compared a supplement containing multiple-source dietary fiber with placebo. The researchers used a combination of resistant dextrin from wheat starch, pectins, insoluble fiber from citrus species, and oat fiber, which also yields β-glucan and starch.

This was provided in 6.5 g servings, containing 5 g of dietary fiber. Of this, about 80% was soluble and 20% insoluble fiber.

Randomized trial tested fiber supplement against placebo

The researchers conducted a single-center, randomized, double-blind, placebo-controlled clinical trial with 54 Caucasian adults who had chronic functional constipation. They were randomly assigned to receive either the fiber supplement or a placebo twice daily for 28 days. In addition, they continued to follow their normal diet. They were instructed on proper defecation, proper fluid intake, and the need to record any other treatments. These steps were aimed at ensuring conformity to real-life use conditions.

They kept a bowel function diary which recorded the number of spontaneous complete bowel movements, time, and stool consistency using the Bristol Stool Form Scale (BSFS). Difficulty in defecation, constipation symptoms such as heaviness, bloating, flatulence, and pain were also explored, as well as the need for laxatives or other measures to induce bowel movements.

Fiber supplement increased bowel movements within two weeks

The treatment group showed a progressive increase in the number of spontaneous complete bowel movements from baseline to 1 week after the last dose, and between consecutive weekly measurements. In contrast, the control group showed a modest increase between baseline and the last week of treatment, but not at the one-week follow-up.

A significant increase in the number of spontaneous complete bowel movements per week was visible between groups from the end of the second week, from one more at the end of week 2 to two more by the end of the follow-up period.

Similarly, stool consistency improved, as reflected by progressively higher BSFS scores during treatment, though it dropped slightly during the follow-up week. The difference was observed from baseline to the end of week 4 and week 5, beginning at 0.55 at the end of week 2 and ending at 1.5 at the end of the follow-up week. The greatest difference, 1.7, occurred at the end of week 4.

The effect of treatment varied across individual constipation symptoms. For instance, abdominal bloating decreased progressively over the treatment period in the treatment group but not in the control group, as did heaviness and abdominal distension. Interestingly, distension was higher in the treatment group at baseline. Flatulence also improved significantly in the treatment group, whereas abdominal pain did not differ significantly between groups.

The supplement was well-tolerated, with no adverse events reported and no participants requiring rescue laxative treatment during the study.

Different fibers may work through complementary mechanisms

The results are supported by a meta-analysis of earlier randomized controlled trials, showing, in particular, the benefits of pectins on bowel function, with high doses of fiber linked to the greatest improvements in stool frequency and consistency when used for over four weeks of treatment.

Oat fiber has also been associated with improvement in multiple constipation-related areas. Resistant dextrin has been shown to act as a prebiotic, increasing the production of short-chain fatty acids by gut bacteria, while also modulating enzyme activity and stabilizing the gut microbiota.

Thus, this combination may have exerted complementary effects on the bowel, improving function and relieving constipation.

Small trial limits broader applicability of findings

The study has several limitations. Its sample size was small, limiting its generalizability. The single-center design and the inclusion of only Caucasian participants further limit the breadth to which the findings can be applied. The duration is too short to measure long-term effects. Residual confounding caused by dietary or behavioral changes cannot be excluded.

In addition, many outcomes relied on participant-reported symptom questionnaires, which are inherently subjective and may be influenced by reporting bias. The one-week follow-up was also too short to determine whether the benefits would persist after treatment stopped.

Combined dietary fibers show promise for chronic constipation

The combination of resistant dextrin, pectins and insoluble fibers from citrus, and oat fibers can provide rapid and clinically meaningful relief from constipation and its symptoms in a population with chronic functional constipation at a daily dose of 13 g. 

This dose is lower than the doses of the individual fiber components typically used separately, while avoiding the discomfort associated with the same dose of resistant dextrin.

Future larger multicenter studies should validate these results, examine how long the improvement persists, and explore changes in the gut microbiota.

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