Constipation

A real trial with a striking result

Chronic constipation affects an estimated 10 to 20% of people worldwide. In a randomised, double-blind, placebo-controlled trial, researchers gave people with chronic constipation a combination of prebiotic fibre and probiotic bacteria. Weekly bowel movements more than doubled, rising from an average of 2.8 to 5.9 per week, a significantly bigger improvement than any group received alone.

Source: Gastroenterology Report, Supplementation with probiotics, prebiotics, and synbiotics in patients with chronic functional constipation

Bigger trials confirm the pattern

A 132-person randomised trial in middle-aged and older adults tested a multi-strain probiotic over 28 days against a placebo, tracking gut bacteria and stool metabolites alongside bowel movement frequency. By day 28, 88% of people taking the probiotic were classed as responders, meaning their bowel movements had genuinely improved, compared with just 26% on placebo. Their gut bacteria shifted too: three helpful groups, Faecalibacterium, Lactobacillus, and Bifidobacterium, increased, while three others, Enterobacter, Collinsella, and Oscillibacter, decreased. A systematic review pooling multiple randomised trials found probiotics significantly increased stool frequency and softened stool consistency overall, with formulas using multiple bacterial strains together outperforming single-strain products.

Source: Efficacy in bowel movement and change of gut microbiota on adult functional constipation patients treated with probiotics-containing products

Fibre works through the same gut bacteria

A separate trial gave adults with self-reported constipation a specific prebiotic fibre, galacto-oligosaccharides, at two different doses. The higher dose increased stool frequency, particularly in people with genuinely low bowel movement frequency at the start and in adults over 35, and produced a clear, dose-dependent rise in Bifidobacterium, a bacteria group already linked to digestive comfort elsewhere in this research.

Source: Prebiotic Galacto-Oligosaccharides Impact Stool Frequency and Fecal Microbiota in Self-Reported Constipated Adults

One organism that physically slows things down

A specific gut organism, Methanobrevibacter smithii, produces methane gas as it ferments food in the gut. This isn't just a passive byproduct. In animal studies, methane gas directly slowed intestinal transit time by 59%, and increased the strength of gut contractions in a way that pushes contents along less effectively. In people, a meta-analysis of 1,277 participants found that testing positive for methane on a breath test was strongly linked to constipation-predominant IBS, with methane-positive people over three times more likely to have this type of IBS.

This has become useful for diagnosis too. A breath test measuring methane has been shown to predict constipation-type IBS with 91% sensitivity, meaning it correctly identifies most people who have the condition, giving doctors a specific, gut-bacteria-based tool rather than relying on symptoms alone.

Source: A novel treatment for patients with constipation: Dawn of a new age for translational microbiome research?

What this means for you

Sudden changes in bowel habits, blood in stool, or unexplained weight loss need medical assessment before assuming ordinary constipation. If constipation is persistent and doesn't respond to diet changes, a doctor can also order a breath test to check for excess methane, since that specific finding points toward a different, more targeted treatment approach than fibre or probiotics alone. For everyday constipation, the trials above point to a real, evidence-backed lever: increasing fibre intake gradually, and considering a multi-strain probiotic if dietary changes alone aren't enough. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.