How Effective are Dietary Therapies in IBS Treatment?

How Effective are Dietary Therapies in IBS Treatment?

Irritable Bowel Syndrome (IBS) is a disorder of altered brain-gut interactions (formerly called functional gastrointestinal disorder) characterized by symptoms of chronically recurring abdominal pain associated with altered bowel habits. Depending on diagnostic criteria used, IBS affects approximately 10% – 20% of the adult population in Western countries, and psychosocial stress as well as diet have been identified as key triggers of symptoms.

Despite its high prevalence, associated medical costs, and impact on patients’ quality of life, available medical treatments have been marginally effective, while behavioral and dietary intervention have shown the greatest therapeutic benefit. Other treatments for IBS include hypnosis, mindfulness-based stress reduction, pre- and probiotics, and herbal therapies. Since diet has been identified as one of the key triggers for IBS symptoms, it is not surprising that some dietary interventions have shown a sustainable benefit in the reduction of IBS symptoms.

A variety of dietary therapies have been applied in IBS treatment, of which traditional dietary advice (TDA), a low FODMAP diet (LFD), and a gluten-free diet (GFD) have received the most attention.

TDA mainly focuses on the adoption of healthy eating patterns, such as the ingestion of regular meals; adequate portion size; sufficient hydration; reduction of alcohol, caffeine, processed foods, fatty foods, and spicy foods; and limiting the intake of sugar as well as gas-producing foods like bread.

The LFD focuses on the elimination of FODMAPs which are short-chain fermentable carbohydrates found in fruit, vegetables, dairy, wheat, and artificial sweeteners. FODMAPs are known to increase the water volume of the small intestine as well as gas production in the colon, both of which can induce gastrointestinal symptoms.

A GFD aims to eliminate gluten-containing products from the diet, including bread, pasta, and other wheat products. Even in individuals without celiac disease, the ingestion of gluten can produce IBS-like gastrointestinal symptoms in about 10% of the general population, which is why the GFD has been become a global trend. It is proposed however, that the efficacy of a GFD in IBS treatment may not be attributed to the removal of gluten per se, but more likely is attributable to the reduction of fructan ingestion, which belongs to the FODMAPs and therefore may contribute to IBS symptoms.

According to a recent large-scale research study led by Imran Aziz from the Sheffield Teaching Hospitals NHS Foundation Trust in the UK, and published in the journal Clinical Gastroenterology and Hepatology, a 50% reduction of IBS symptoms was observed after a 4-week dietary intervention (which was confirmed with a nutrition assessment questionnaire) in 14 out of 33 patients on TDA, 18 out of 33 patients following LFD, and 19 out of 33 patients on the GFD. This means that the reduction in IBS symptoms was not significantly different between the 3 diets (p = 0.43). Although the differences were not statistically significant, it was observed that the GFD tended to have the highest efficacy in the treatment of IBS followed by the LFD, then TDA.

The results were independent of mode of delivery of dietary advice, which was either virtual or face-to-face. However, the study participants found the TDA much cheaper, less time-consuming, and easier to adhere to than either the LFD or GFD. While slightly more effective, the LFD and GFD may be more inconvenient, more expensive, and harder to follow, which is why TDA is still the most used dietary therapy amongst medical professionals.

However, the decision about which dietary therapy should be implemented needs to be made to match the patient’s individual preference, need, and life situation, and therefore should be made in dialogue with the patient.

The authors of this study suggested that the underlying IBS-reducing benefits of each of these diets may be attributed to the reduction in FODMAP intake, a characteristic shared by all three dietary therapies. However, the underlying mechanisms of action remain incompletely understood, including a role of the gut microbiome.

In addition, it needs to be emphasized that a long-term low FODMAP diet is inconsistent with gut microbial health, as it deprives the microbes of complex carbohydrates, their main source of food. It contradicts current recommendations of a healthy diet high in multiple types of fiber and polyphenols.

In summary, all 3 dietary approaches, TDA, LFD, and GFD were shown to be somewhat effective in reducing IBS symptoms even though there was no significant difference between them. Currently, TDA is still the most popular approach due to its patient friendliness. Given the small differences in symptom improvement, the negative health effects of a chronic low FODMAP diet, and the inconvenience and cost of a gluten-free diet, LFD and GFD should not be considered first line therapies and should probably be reserved for patients who have not responded to other more effective therapies.


Jill Horn is an international student from Switzerland on a pre-med track, currently majoring in Neuroscience at UCLA.