The evidence is mixed: eating more fibre is worthwhile for mild constipation, but in more severe or unexplained constipation extra fibre can worsen symptoms. A Mediterranean or plant-based dietary pattern appears protective in large observational studies, independently of fibre intake. For older adults, robust studies that specifically determine what works best for their situation are still lacking.
A high-fibre diet does not work equally well for everyone when it comes to constipation, and in some people it actually makes symptoms worse. For mild constipation, eating more fibre is still considered a sensible first step. But in so-called idiopathic constipation, constipation without a clear cause, extra fibre can worsen feelings of bloating and straining rather than relieving them. The simple advice to 'eat more fibre' is therefore an oversimplification.
A small Singaporean study involving 63 patients produced a striking result: people who stopped eating fibre altogether went from one bowel movement every 3.75 days to one bowel movement per day. Symptoms such as bloating and straining disappeared completely in the no-fibre group, while those symptoms persisted in people who continued eating fibre. This is an intriguing finding, but the study was small, had no control group, and has not yet been confirmed in larger research. It does not mean that everyone with constipation is better off without fibre, only that in a specific group the conventional approach can backfire.
What does appear to offer consistent protection is a Mediterranean or plant-based dietary pattern as a whole. In three large American cohorts with more than 95,000 middle-aged and older participants, such a dietary pattern was linked to 16% and 20% lower odds of developing constipation, respectively. A Western dietary pattern was associated with 22% higher odds. Notably, this association was independent of how much fibre a person ate. Vegetables and nuts appeared to be the most protective components. This is an association study, so whether this reflects true cause and effect has not yet been established.
For older adults aged 60 and above, guidelines recommend fibre supplements, such as psyllium, as a first step alongside other lifestyle adjustments. It is important that fibre intake is increased gradually in order to limit side effects such as bloating. However, solid evidence specifically for this age group is lacking in the available studies. In older adults, physical inactivity and other factors also play a role, making it difficult to pinpoint a single cause of bowel complaints.
A commonly heard piece of advice is to drink more fluids to combat constipation, but this does not hold true for most people. Research shows no effect of increased fluid intake on constipation, unless a person is actually dehydrated. This advice is therefore not supported by the evidence.
Based on multiple observational cohorts (up to more than 95,000 participants), a small RCT-like study without a control group (n=63), and guideline articles. No large randomised trials specifically in older adults were found in the sources provided.