Eating a Wider Variety of Foods May Ease Constipation by Reshaping Gut Bacteria

Chronic constipation is one of the most common gastrointestinal complaints worldwide, affecting up to 15.3% of the global population depending on the diagnostic criteria used. Dietary modification is a standard recommendation, but whether the sheer variety of foods a person eats matters as much as any single nutrient has been unclear. A new cross-sectional study published in the journal Nutrition suggests that dietary diversity scores are positively associated with bowel movement frequency in people with functional constipation, and that shifts in the gut microbiota may help explain why.

Dietary Diversity Score and Bowel Movement Frequency in Functional Constipation

The study, led by Tang A and colleagues, enrolled 250 participants aged 18 to 70 years who had been diagnosed with functional constipation (FC). FC is a condition defined by persistently difficult, infrequent, or incomplete defecation without an identifiable structural or biochemical cause. Researchers assessed what participants ate using food frequency questionnaires and converted those responses into a Dietary Diversity Score (DDS) ranging from 0 (the lowest variety) to 8 (the highest). The result: higher DDS was positively associated with bowel movement frequency (BMF), with a trend P-value of 0.012. In plain terms, participants eating from a broader range of food categories tended to report more frequent bowel movements. Parallel research in adult women in the United States has found similar links between diet quality scores and lower constipation rates, adding some cross-population weight to this direction of evidence.

Why Gut Bacteria Could Be the Mechanism Behind This Link

The microbiota findings are where the study gets more specific. Gut microbiota composition was measured using 16S ribosomal RNA amplification, a widely used sequencing approach that identifies bacterial genera from stool samples. Across the 121 genera evaluated, one stood out: the Ruminococcus torques group showed a strong inverse correlation with bowel movement frequency (beta = -0.901, P < 0.001, false discovery rate P = 0.022). That means participants who harbored more of this bacterial group tended to have fewer bowel movements. The same group was also potentially correlated with dietary diversity scores (beta = -0.142, P = 0.029), though this association did not survive multiple-testing correction (false discovery rate P = 0.116), so that particular link should be treated cautiously. Beyond individual genera, the distribution of gut microbial enterotypes, broad compositional patterns in the microbiome, differed both by DDS level and by weekly bowel movement frequency. The picture that emerges is one where what you eat may influence which bacterial communities dominate, and those communities may in turn influence how regularly you go.

How the Cross-Sectional Design Shapes What the Study Can Show

The researchers used a cross-sectional design: everyone's diet and microbiome were measured at a single point in time rather than tracked over months. That approach is useful for identifying associations, but it cannot establish which came first. Did low dietary diversity cause an overgrowth of Ruminococcus torques, which then slowed bowel transit? Or did pre-existing constipation change eating habits in ways that drove diversity down? The data cannot answer that. Distinguishing association from causation remains one of the central challenges in microbiome research, and this study is no exception. Dietary intake was also captured through food frequency questionnaires, a self-report method that introduces recall error and varies considerably across individuals, which is a known limitation of diet-microbiome research generally.

Open Questions About Ruminococcus torques and Constipation Severity

The role of the Ruminococcus torques group deserves attention as a thread for future work. Ruminococcus torques is a mucus-degrading bacterium associated with compromised intestinal barrier function in some contexts, but its specific role in bowel transit and constipation pathophysiology is not well characterized. The correlation observed here was among the strongest in the dataset, but the study was not designed to isolate its mechanism. It also bears noting that gut microbiome responses to diet are highly individual: research has shown that even large reductions in dietary variety do not produce uniform microbiome shifts across people, which complicates any simple story about diversity driving specific bacterial changes. Whether the Ruminococcus torques association holds in larger or more ethnically diverse samples, and whether it reflects cause or consequence, remains to be established.

What Comes Next for Dietary Interventions in Functional Constipation

For now, the findings are consistent with the general clinical guidance that broader, more varied diets tend to support gastrointestinal health, but they add a microbiome-level layer to that advice. A 250-person cross-sectional study in a predominantly Chinese population is a starting point, not a conclusion. Longitudinal trials that track how deliberately increasing dietary diversity affects both gut bacteria and constipation symptoms over time would be the logical next step. So would mechanistic work on Ruminococcus torques, given its apparent connection to both diet quality and stool frequency in this dataset. Functional constipation is a condition that affects hundreds of millions of people globally, and dietary interventions are appealing precisely because they are accessible and low-risk. Studies like this one build the biological rationale for taking variety seriously as a therapeutic variable, even if the causal story is still being written.

Evidence rating

EMERGING — 80/100

Caveats:

• Cross-sectional design means this study shows association, not causation — it cannot confirm that increasing dietary diversity directly improves constipation.
• The correlation between Ruminococcus torques group and dietary diversity did not survive false discovery rate correction (FDR P = 0.116), so that specific link remains tentative.
• Study population was limited to Chinese adults with functional constipation; findings may not generalise to other populations.
• Funding source was not disclosed by the authors.

Cross-sectional study of 250 adults with functional constipation. Findings show associations between dietary diversity, bowel movement frequency, and gut microbial composition — including a named genus with a quantified effect size — but the design cannot establish causation. The proposed microbial mediator (Ruminococcus torques group) did not reach significance after false discovery rate correction for the dietary diversity link, and the findings have not yet been independently replicated.