Chronic Constipation: What Does the Nutrition Evidence Really Say?
Can changing your diet help chronic constipation? Discover what the latest evidence says about fibre, probiotics, kiwifruit, magnesium, rye bread and mineral water.
If you have chronic constipation, you've probably heard the usual advice: “Eat more fibre and drink more water.”
But is it really that simple?
New evidence-based guidelines from the British Dietetic Association (BDA) provide a more specific look at which dietary strategies may actually help. And some of the findings may surprise you.
Let's separate a few common constipation myths from the evidence.
1. “More fibre is always better.”
Evidence: Not necessarily.
Fibre can help constipation, but more isn't always better. Increasing fibre too quickly can cause bloating, gas and abdominal discomfort.
The strongest evidence is for specific fibre supplements, particularly psyllium. Doses above 10 g per day, taken for at least four weeks, may improve stool output, reduce straining and improve constipation symptoms.
Interestingly, the guidelines did not recommend simply following a generic “high-fibre diet” because there isn't enough high-quality evidence to support a specific whole-diet approach.
Take-home: Fibre can help, but focus on the type, amount and your individual tolerance.
2. “Probiotics will fix constipation.”
Evidence: Maybe, but it depends on the strain.
Some probiotic strains, including Bifidobacterium lactis, may improve constipation. However, there isn't enough evidence to recommend one specific probiotic for everyone.
If you want to try one, a four-week trial following the manufacturer's instructions is reasonable.
Take-home: Probiotics may help, but they're not a guaranteed solution.
3. “Kiwifruit is just a gut-health trend.”
Evidence: This one has research behind it.
Eating 2–3 kiwifruit daily for at least four weeks may improve constipation.
Kiwifruit may also be a useful alternative for people who experience bloating or abdominal discomfort with psyllium.
Take-home: Kiwifruit is a simple food-based option worth considering.
4. “Magnesium is harmless because it's natural.”
Evidence: Magnesium oxide may help but isn't suitable for everyone.
Magnesium oxide 0.5–1.5 g per day for at least four weeks may improve constipation when clinically appropriate.
However, magnesium can cause gastrointestinal side effects and may not be suitable for people with certain medical conditions, particularly kidney problems.
Take-home: Check with your doctor or pharmacist before starting magnesium supplements.
5. “Rye bread can't possibly affect constipation.”
Evidence: It may.
Studies suggest that 6–8 slices of rye bread daily for at least three weeks may improve constipation.
However, that's a lot of bread and may not be practical, or comfortable, for everyone.
Take-home: Rye bread is an evidence-supported option, but it doesn't need to become your entire diet.
6. “Drinking more water will fix constipation.”
Evidence: The type of water may matter.
The guidelines found that 0.5–1.5 L of high-mineral-content water per day for 2–6 weeks may improve some constipation outcomes.
However, there is currently no standard definition of what counts as “high-mineral-content” water.
Take-home: Stay adequately hydrated, but don't assume that drinking huge amounts of plain water will solve constipation.
So, what should you actually try?
There isn't one “constipation diet” that works for everyone.
The current evidence supports several specific options:
Psyllium/fibre supplements: >10 g/day for at least 4 weeks
Kiwifruit: 2–3 per day for at least 4 weeks
Probiotics: some strains may help; evidence is still limited
Magnesium oxide: 0.5–1.5 g/day when clinically appropriate
Rye bread: 6–8 slices/day was studied for at least 3 weeks
High-mineral-content water: 0.5–1.5 L/day for 2–6 weeks
The important message is that you don't need to try everything at once. Choose an approach that suits your preferences and tolerance, give it enough time, and assess whether it actually helps.
And remember: evidence-based doesn't mean guaranteed to work for everyone.
If constipation is persistent, severe, suddenly different, or associated with blood in the stool, unexplained weight loss, vomiting or significant abdominal pain, seek medical advice.
Forget the search for a “magic” constipation food. The best approach is one that is evidence-based, practical and works for you.
References
Dimidi E, et al. British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults. Journal of Human Nutrition and Dietetics. 2025.
Dimidi E, et al. Systematic reviews and GRADE-based evidence underpinning the BDA dietary guidelines for chronic constipation. 2025.