Diet modification in constipation

• diets with a high fibre content are effective in increasing stool weight and bowel movement frequency
  • the effects of a high fibre diet (e.g. approximately 30g per day) may occur after a few days
  • however a high fibre diet should be tried for at least a month before its effects are determined
• it is important to ensure an adequate fluid intake (e.g. two litres of water/day) if a patient is on a high fibre diet
  • note though that drinking this amount of fluid is problematic for some people
• a high-fibre diet should be used with caution in patients who have obstructive symptoms or faecal impaction, and may be ineffective in slow-transit constipation (e.g. secondary to opioid use) or if constipation is caused by a defecatory disorder (1)
• there is evidence from observational studies suggest an association between constipation and reduced physical activity - therefore encouraging exercise is especially good health advice for patients with constipation, where lack of mobility may be a contributing factor

Guidelines from the British Dietetic Associate (BDA) with respect to the dietary management of constipation note (2):

Summary recommendations:

• psyllium supplements, certain probiotic strains, magnesium oxide supplements, kiwifruits, rye bread and high mineral water are recommended to improve specific constipation outcomes.

Fibre supplements: Good Practice statements

• fibre supplement doses above 10 g/d are optimal for increasing the number of people with constipation who have a clinical benefit, improving stool output and reducing the severity of straining (evidence-based recommendation)
• consuming fibre supplements for a minimum duration of 4 weeks is optimal for increasing stool frequency and improving global constipation symptoms of constipation (evidence-based recommendation)
• in people with constipation who experience tolerance issues with fibre, fibre supplement intake may be increased gradually with weekly increments to avoid adverse effects, such as bloating and flatulence (expert opinion recommendation)
• when advising the use of inulin-type fructan supplements in constipation, the possibility of increased flatulence should be discussed (evidence-based recommendation)
• fibre supplements should be accompanied by additional fluid intake where clinically appropriate (expert opinion recommendation)

Probiotic supplements: Good Practice statements

• though some species and strains of probiotics, such as B. lactis and Bacillus coagulans Unique IS2, may improve constipation, in general, there is a lack of convincing evidence to recommend specific strains of probiotics in constipation (evidence-based recommendation)
  • therefore, clinicians may support patients who wish to try probiotics, and advise them to try a probiotic brand of their choice for at least 4 weeks, following the instructions recommended by the manufacturer (expert opinion recommendation)

Magnesium oxide supplements: Good Practice statements

• magnesium oxide supplements at a dose of 0.5–1.5 g/d for at least 4 weeks may be recommended in constipation, as clinically appropriate (evidence-based recommendation)
  • magnesium oxide supplements may be increased gradually with weekly increments, while monitoring tolerance, starting at a dose of 0.5 g/d (evidence-based recommendation)

Kiwifruits: Good Practice statements

• consumption of 2–3 kiwifruit daily for at least 4 weeks may be recommended in constipation (evidence-based recommendation)
• Kiwifruit without skin may be recommended for constipation (evidence-based recommendation). While not assessed in studies, keeping the skin on will provide additional fibre, which may potentially be beneficial, but may also potentially increase side effects (expert opinion recommendation)
• Kiwifruit may be a preferred option over psyllium in people with constipation who experience side effects such as bloating, abdominal pain and flatulence (evidence-based recommendation)

Rye bread: Good Practice statement

• consuming 6–8 slices of rye bread daily for at least 3 weeks may be recommended in constipation, (evidence-based recommendation), however, this may not be realistic or manageable for some patients

Reference:

1. MeReC Bulletin (2004); 14(6)21-4.
2. Dimidi E, van der Schoot A, Barrett K, Farmer AD, Lomer MC, Scott SM, Whelan K. British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults. Neurogastroenterol Motil. 2025 Oct 13:e70173.