There is a lack of evidence for high-fiber diets to control constipation. This is what works

Chronic constipation is common, but available nutritional advice is vague

Chronic constipation, defined as less than three bowel movements per weekHard stools or difficulty urinating without underlying pathology is a long-term condition that affects quality of life and imposes an economic burden on both patients and healthcare systems. Chronic constipation is due to a wide range of causes, with emerging research suggesting that intestinal transit may impact the gut microbiota, opening up new ways to manage constipation.

For years, nutritional advice for constipation was vague, with people told to increase fiber intake and drink more water¹.

The first-ever evidence-based dietary guidelines for adults with chronic constipationled by researchers at King’s College London and endorsed by the British Dietetic Association (BDA), concludes Kiwis, rye bread, high mineral water, psyllium husk supplements, certain probiotic strains and magnesium oxide supplements can all help relieve chronic constipation^2.3.

A group of experts reviewed more than 75 clinical studies that led to 59 clear recommendations on which supplements, foods, drinks and whole diets work for constipation. Unlike previous guidelines, the new dietary recommendations for constipation are based on four rigorous systematic reviews and meta-analyses, which summarize reliable studies published to date.

Some foods can help relieve constipation by altering the gut microbiota and increasing fecal weight

One of the most important findings is that eating 2-3 kiwis per day (with or without skin)8-10 prunes per day, some rye bread and replacing tap water with water with a high mineral content can help relieve chronic constipation. It’s worth noting that kiwifruit was associated with fewer side effects than prunes or psyllium supplements. Kiwifruit was the food that was more effective at increasing stool frequency, thanks to its fiber, which increases stool volume and water content in the intestines, which can soften stool, and actinidin, which promotes protein digestion in the stomach and small intestine.

There is no nutritional component involved in its benefits for constipation. In particular, plums and kiwifruit have been shown to alter the gut microbiota, with plums increasing fecal weight and kiwifruit increasing small intestinal and fecal water content.⁴. The new guidelines suggest that it is wise to try foods that work against constipation for at least four weeks^2.3.

The new guidelines also show that some supplements can help improve constipation, including: psyllium fiber supplements, some probiotic strains (e.g. Bifidobacterium lactis, Bacillus coagulans lilac-01, Lactobacillus reuteri DSM-17938, en Escherichia coli Nissle 1917), and magnesium oxide supplements. Psyllium is a type of fiber that forms a gel-like substance and can add volume to the digestive material and prevent constipation. It showed consistent benefits for constipation across studies, especially when used at higher doses (>10 g/day) and with longer treatment duration (³4 weeks).

It appears that some probiotics can increase intestinal transit time and the number of weekly bowel movements and help stool pass more easily by affecting immune cells in the intestines, forming the composition of the intestinal microbiota and fermentation byproducts, which in turn appear to influence intestinal motility via the intestinal nervous system.⁵. The byproducts of the gut microbiota, called short-chain fatty acids, increased by some probiotics, also appear to be involved in improving intestinal transit time.

Which nutritional advice does not work for constipation?

Take Senna supplements (a type of laxative)synbiotics and some probiotics did not seem to work well for constipation. There was also no strong evidence for eating a high-fiber diet, even though fiber is still essential for overall gut health, longer life and a reduced risk of heart disease, diabetes and some types of cancer.

Additionally, there is also a lack of research on the role of prebiotic fibers that nourish our gut microbes and contribute to a healthy gut microbiome.

Takeaways

• Kiwis, plums and some probiotic strains can help relieve constipation by shaping the gut microbiota and increasing stool weight.
• Other dietary interventions that may help constipation include rye bread, high-mineral psyllium husk supplements, and magnesium oxide supplements.
• Taking senna supplements, synbiotics and prebiotics does not seem to work well for constipation.
• Remember to gradually increase the dose of all foods or supplements to avoid bloating or excessive flatulence. If constipation persists or is accompanied by other complaints, or if you would like tailored advice, it is important to talk to a registered dietitian or consult a doctor.

References:

1. The Lancet Gastroenterology Hepatology. Bridging the evidence gap in the nutritional approach to intestinal disorders. Lancet Gastroenterol Hepatol. 2025; 10(12):1053. two: 10.1016/S2468-1253(25)00326-7.
2. Rejects E, goes to school, Barrett K and all. British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults. J Hum Nutr Diet. 2025; 38(5):e70133. doi:10.1111/jhn.70133.
3. Rejects E, goes to school, Barrett K and all. British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults. Neurogastroenterol Motil. 2025; 37(12):e70173. doi: 10.1111/nmo.70173.
4. Katsirma Z, Ontslag E, Mats A and al. Fruits and their impact on the intestinal microbiota, intestinal motility and constipation. Food Function. 2021; 12(19):8850-8866. two: 10.1039/d1fo01125a.
5. Dimidi E, Scott SM, Whelan K. Probiotics and constipation: mechanisms of action, evidence for effectiveness and use by patients and healthcare professionals. According to Nutr Soc. 2020; 79(1):147-157. doi: 10.1017/S0029665119000934.