Patients with gastrointestinal diseases often experience symptoms (diarrhea, constipation, abdominal pain, bloating) that worsen after a meal. They draw linkages between what they eat and negative consequences for their well-being. In an attempt to self-manage, patients often end up removing foods from their diet that are needed for nutritional health. They turn to their medical practitioners for information and support – and often, physicians are not confident in up-to-date practice of diet and its impact on gut function and the gut microbiota.

The World Gastroenterology Organization (WGO) Guidelines on Diet & The Gut aims to provide up-to-date practice recommendations to medical practitioners around the world. The recommendations take into account the available evidence, research, expert consensus and existing guidelines, to provide strategies to support patients’ gut health.  Most importantly, they created a cascade of recommendations around fiber intake, the low FODMAP diet, and various food intolerances as they pertain to overall health, and the gut microbiota composition and diversity.

There is a large ‘fiber gap’ in developed countries – with the average intake of fiber far below the recommended levels – which needs to be addressed. The primary recommendations focus on bridging the fiber-gap, the role of different fibers for the gut microbiota, and how fibers influence a variety of gastrointestinal conditions which patients may look to manage through dietary intervention. These topics are reviewed from an individual, policy, and food industry perspective to elucidate how to bridge the ‘fiber gap’ and improve digestive health globally. Strategies include improving access and encouraging intake of plant-based foods, and eventually add fiber supplements to mitigate the fiber gap.

In certain gastrointestinal conditions, e.g. with abdominal pain, individuals often choose to minimize intake of fibre-rich foods to manage their gut symptoms, which can have negative consequences on the gut microbiota. To understand how fibers affect gastrointestinal conditions and symptoms, the guidelines compare and contrast different fibers´ fermentability, solubility, impact on transit time, and easing defecation.  With the help of these guidelines, practitioners can better understand how fibers impact the gut microbiota and symptoms of their patient, and tailor recommendations for those with gastrointestinal disorders, like irritable bowel syndrome (IBS).

In managing IBS – one of the most common gastrointestinal diagnoses – the role of the low FODMAP diet and its impact on the gut microbiota is reviewed. The review highlights the importance of support from a trained professional to ensure dietary adequacy.  When implemented under supervision of a trained practitioner, the low FODMAP diet has the ability to improve IBS symptoms in approximately 75% of patients at short term. Celiac disease should be adequately excluded before proceeding on a trial of the low FODMAP diet for a maximum for 2-6 weeks, followed by strategic reintroduction and maintenance phases. More data is needed to assess the safety and impact of the low FODMAP diet on vulnerable populations with greater nutrient needs, such as children, and during pregnancy – however for the general population, the low FODMAP diet can be nutritionally adequate if special care is taken.

Questions remain about the impact the low FODMAP diet has on gut microbiota, particularly on its reduction of fermentable carbohydrates, and how that influences our gut microbiota. Research suggests that the low FODMAP diet may reduce bacterial abundance, and cause a subsequent loss of bifidobacteria. A small-scale trial looking at the impact reintroduction of FODMAP’s had on the gut microbiota, found that there were no differences in microbial composition once FODMAP’s were part of the regular diet again at an individual amount the patients tolerated – however, the long term consequences of the low FODMAP diet are yet to be elucidated.

In regard to non-celiac gluten sensitivity, gluten has yet to be demonstrated to be a causal factor for IBS symptoms through rigorous scientific studies. At this point, evidence suggests other components of wheat, such as fructans – a fermentable carbohydrate found in wheat – may be the reason why patients see a symptom improvement following a gluten free diet. The gluten free diet is not an appropriate intervention to manage IBS symptoms, though many patients self-prescribe such a diet – practitioners therefore should be prepared to address gaps in patient understanding and barriers to change.

It is clear that many individuals self-diagnose and self-manage their gastrointestinal disorders with nutrition interventions. It is important for medical professionals to understand the impact these self-management strategies have on adequate fiber intake, dietary variety, and on symptoms. Through a better understanding of the evidence, as well as through a cascade of recommendations provided by the WGO, health care professionals may use science-based knowledge to properly guide patients in managing their gut symptoms, while maintaining nutritional adequacy.



Makharia, Govind, et al. (2018). Diet & the Gut. World Gastroenterology Organisation Global Guidelines. Retrieved from:

Staudacher, H. M. (2017). Nutritional, microbiological and psychosocial implications of the low FODMAP diet. Journal of gastroenterology and hepatology, 32(S1), 16-19. DOI: 10.1111/jgh.13688

Halmos, E. P., Christophersen, C. T., Bird, A. R., Shepherd, S. J., Gibson, P. R., & Muir, J. G. (2014). Diets that differ in their FODMAP content alter the colonic luminal microenvironment. Gut, gutjnl-2014. DOI: 10.1136/gutjnl-2014-307264