Alderson et al are to be congratulated on a clear and pragmatic presentation of the management of IBS.1 They based their recommendations for the dietary management of IBS on the best evidence we have. But caution is needed when considering the implications of the best evidence for dietary manipulation because the results are not clear cut. A meta-analysis found that both a low-FODMAP diet (LFD) and the Mediterranean diet improve overall symptoms and quality of life.2 The review found several studies of LFD but only one for the Mediterranean diet. Thus we have more evidence for the effectiveness of LFD. On the other hand, the Mediterranean diet had a greater effect. Of the two, the LFD is harder to apply. So far, it would seem sensible to recommend the Mediterranean diet first in primary care and that LFD be reserved for non-responsive or more severe cases. A clear plan for dietary management? I am not sure. There seems to be a contradiction. The Mediterranean diet, replete with pulses, wheat products, fruit, onions, and brassicas, is high in FODMAPs. How can both it and an LFD be effective? Another review found that soluble fibre (as found in oats and products like ispaghula) is effective for global symptoms but insoluble fibre (Mediterranean) may worsen some symptoms.3 However, the review had several shortcomings. It did not fully describe the inclusion criteria and there was no risk of bias assessment.
There is another problem when it comes to translating research into practice: research on dietary management has focused on constipation, pain, and bloating. But what are we to suggest for patients with mixed constipation and diarrhoea (IBS-M)?
For me, the message is that we should share the uncertainty about diet with patients, then guide them to explore the effects of different diets over a suitable period with the warning that they may not find an answer. Future research should look further into the Mediterranean diet, include IBS-M, and explore better the difference between soluble and insoluble fibre. We might then be able to give our patients more accurate guidance.
- © British Journal of General Practice 2026
