Chronic constipation is one of the most common conditions of gut-brain interaction, affecting approximately 1 in 10 adults worldwide. It has a significant impact on quality of life and carries economic burdens such as direct costs and reduced productivity.¹.

New evidence suggests that Intestinal transit time is an important factor in shaping the composition and metabolic activity of the intestinal microbiotawhich can lead to constipation and affect long-term gut health. To manage symptoms of constipation, people often first try dietary changes, but existing guidelines for constipation management typically include limited dietary advice, primarily focused on increasing fiber intake and ensuring adequate fluid intake.¹.

New guidelines from the British Dietetic Association (BDA) provide the first comprehensive, evidence-based recommendations for the use of supplements, food and drink, and whole diets for chronic constipation.^{2, 3}.

The guidelines were developed through four systematic reviews and meta-analyses of 75 randomized controlled trials and evaluated using the GRADE approach with a Delphi consensus process.

The guidelines include a total of 59 recommendations. Evidence supporting the use of kiwifruit, prunes, rye bread, and high-mineral water. Six randomized controlled trials (RCTs) showed that consuming two to three kiwifruit per day may increase bowel movements and reduce overall intestinal symptoms. In particular, kiwifruit had fewer side effects than prune and psyllium supplements. Furthermore, two RCTs showed that eating six to eight slices of rye bread a day may increase bowel movements and shorten intestinal transit time, but may worsen intestinal symptoms compared to white bread. High mineral content water was another intervention that improved response to treatment in four RCTs compared with tap water or low mineral content water.

Perhaps the synergistic effects of multiple components in foods are responsible for their effects on specific outcomes of constipation. Prunes and kiwifruit in particular have been shown to alter the gut microbiome in human studies, with prunes increasing fecal weight and kiwifruit increasing water content in the small intestine and feces.⁴. To what extent does water with high mineral content improve constipation through the formation of intestinal microbiota? unknown.

In addition to food and drink, several supplements can help relieve constipation. Psyllium supplements, kiwifruit supplements, magnesium oxide supplements, and certain probiotic strains may improve certain constipation outcomes. Multiple RCTs (n = 16) consistently showed that psyllium (Ispagula fiber) can improve bowel movement and straining, with optimal effects achieved at doses greater than 10 g/day and longer treatment periods (approximately 4 weeks). Based on 30 RCTs investigating probiotics, their effects were species, strain, and outcome specific. especially, Bifidobacterium lactis, bacillus coagulans Lilac-01, L. reuteri DSM 17938, and Escherichia coli Nissle 1917 may improve bowel movement frequency. Kiwifruit supplements may improve incomplete bowel movements and abdominal pain. Magnesium oxide supplements (0.5 to 1.5 g/day) have been shown to consistently improve constipation outcomes, including response to treatment, bowel frequency, stool consistency, and overall constipation symptoms. Please note that the dosage should be gradually increased to a monitored and tolerated level.

The mechanisms by which probiotics affect intestinal motility and constipation include effects on intestinal regulatory T cells, gut microbiota formation, and fermentation byproducts, which are thought to influence intestinal motility through the enteric nervous system rather than the brain-gut axis.⁵.

but, There was insufficient evidence to support a whole-food approach to constipation, including the traditional advice to adopt a high-fiber diet.. In addition, certain probiotics (e.g. Lactobacillus casei Shirota), prebiotics (inulin-type fructans softened stool consistency but had no clinically meaningful effect), synbiotics, and senna supplements. Additionally, no eligible RCTs were found for oats and flaxseed, so we cannot make recommendations regarding their benefits for constipation.

Clinician-friendly tools have also been developed to support implementation of these guidelines in daily practice.

The BDA guidelines for chronic constipation emphasize the importance of high-quality evidence to guide dietary therapy to manage impaired gut-brain interactions. It also reminds us that nutrition clinical trials face more challenges than trials of pharmacological interventions, especially considering methodological issues, complex composition of foods, and compliance monitoring. Impact of background diet and diet-microbiome interactions on research results⁶.

Current evidence does not support some dietary treatments targeting the gut microbiome in healthy adults with chronic idiopathic constipation, but they may be worth trying in certain clinical situations. For example, fermented milk containing probiotics and prebiotics is used for patients with Parkinson’s disease. Shown to improve constipation without serious adverse events. Evidence of the benefits of dietary interventions on constipation outcomes allows health care professionals to offer adult patients with chronic constipation effective options instead of vague advice to eat more fiber, drink more water, and do more physical activity.

References:

1. Lancet Gastroenterology Hepatology. Filling the evidence gap in dietary approaches to intestinal disease. Lancet Gastrointestinal Roll Hepatol. 2025;10(12):1053. doi: 10.1016/S2468-1253(25)00326-7.
2. Dimidi E, van der Schoot A, Barrett K, et al. British Dietetic Association guidelines for dietary management of chronic constipation in adults. J Ham Nuttle Diet. 2025;38(5):e70133. doi: 10.1111/jhn.70133.
3. Dimidi E, van der Schoot A, Barrett K, et al. British Dietetic Association guidelines for dietary management of chronic constipation in adults. neurogastrointestinal rollmotil. 2025;37(12):e70173. doi: 10.1111/nmo.70173.
4. Katsirma Z, Dimidi E, Rodriguez Mateos A, et al. Fruits and their effects on intestinal flora, intestinal motility, and constipation. Function of food. 2021; 12(19):8850-8866. doi: 10.1039/d1fo01125a.
5. Dimidi E, Scott SM, Whelan K. Probiotics and constipation: mechanism of action, evidence of effectiveness, and use by patients and health professionals. Proc Nutr Soc. 2020; 79(1):147-157. doi: 10.1017/S0029665119000934.
6. Staudacher HM, Yao CK, Chey WD, et al. Optimal design of clinical trials of dietary interventions in gut-brain interaction disorders. Am J Gastroenterol. 2022; 117(6):973-984. doi: 10.14309/ajg.0000000000001732.