A new dietary approach for the treatment of irritable bowel syndrome

Irritable bowel syndrome frequently occurs with comorbid depression, but traditional treatment just targets the troubling gut symptoms. A recent study tells us a new dietary approach may be able to treat both.

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder that affects around 4% of the Australian population. People with IBS experience recurrent abdominal pain and altered bowel habits, often accompanied by other symptoms such as bloating. IBS can range from mild to severe and in many cases can limit social activities and the ability to work and affect overall quality of life.

The past 15 years have seen significant advances in understanding of the aetiology of IBS. This better understanding has necessitated shifts in care from a medical-centric to a broader integrated care focus, including medical, dietary and psychological treatment. Australian researchers led the way in our understanding of how restriction of specific dietary carbohydrates termed “FODMAPs” (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) could benefit people with IBS symptoms. Consequently, dietitians have rapidly become fundamental in the care of people with IBS around the world, as diet features prominently in treatment pathways and clinical guidelines.

The contribution of gut–brain dysregulation in driving gut symptoms has also become increasingly clear, as has a greater appreciation of the high prevalence of psychological comorbidity in IBS (eg, ~30% of people with IBS in Australia have anxiety or depressive symptoms). Psychologists are also now increasingly recognised as key members of the integrated care team for IBS, with cognitive behavioural therapy and gut-directed hypnotherapy for treatment of IBS symptoms backed by strong evidence.

The complexity of comorbid depression

Depression is a leading contributor to the global burden of disease. In IBS, a quarter of people experience a depressive disorder, a rate three times higher than people without IBS. Depression can often mean difficulties in engagement in self-care and higher rates of health care seeking, with the need to consider these by clinicians in their treatment approach well recognised. In Australia, treatment guidelines for depression have transitioned from psychotropic medication with talking therapies as first-line treatment to include lifestyle change as foundational. From a dietary perspective, there is growing evidence that a Mediterranean diet – which focuses on extra virgin olive oil, fruit, vegetables, wholegrains, nuts and seeds, fish, and small quantities of red meat and processed foods – reduces depressive symptoms and may drive a considerable rate of remission.

Testing the Mediterranean diet with people with IBS and depression

The effects of a Mediterranean diet in depression are theorised to occur via modifying gut microbiome. These trillions of organisms in our gut are active participants in constant communication between our gut and brain, and so it makes sense that modulating the gut microbiome could have an impact on psychological symptoms. Interestingly, in IBS, beneficial modulation of the microbiome also improves gut function. Could a Mediterranean diet, therefore, potentially improve both gut and psychological symptoms in people with IBS?

The randomised-controlled trial of Mediterranean diet for people with IBS (and mild to moderate depression or anxiety), led by this article’s first author, was the first of its kind. We wanted to firstly test whether a Mediterranean diet was even feasible in people with IBS. This diet is inherently rich in high FODMAP foods – could people with IBS who are known to have heightened sensitivity to FODMAPs even follow it? We randomly assigned people either to the Mediterranean diet dietary counselling from a dietitian or to continue their habitual diet for a period of six weeks. We found people could stick to the diet – the Mediterranean diet adherence score was modestly higher in the treatment group versus controls at week 6.

Also, and quite astonishingly, 83% of participants on the Mediterranean diet had a 50-point reduction in their IBS gut symptom severity score compared with only 37% in the control group. Improvements in symptoms of depression were also greater in the Mediterranean diet group compared with the control group (52% v 20% achieving a clinically meaningful improvement in depressive symptoms). We were, however, not able to relate these improvements in gut and depressive symptoms directly to changes in gut microbiome – larger trials are needed to help uncover the underlying mechanisms.

For the first time we showed that people with IBS can adhere to a Mediterranean diet and appear to experience improvements in both gut and psychological symptoms. More research is needed to confirm these findings, but we think this trial has opened a new line of thinking for how to care for people with IBS and comorbid depression and/or anxiety.

What does this mean for dietary treatment of IBS?

Our recent review provides comprehensive discussion on the multidisciplinary approach to managing people with IBS who also experience depression or anxiety. Treatments should be guided by the degree of gut and psychological symptom severity. From a dietary perspective, we recommend standard dietary approaches (healthy eating guidelines), the low FODMAP diet, the Mediterranean diet or a combination, based on individual needs. With the help of an expert dietitian, people with IBS can successfully implement elements of more than one dietary approach if necessary. In people with severe gut symptoms but low psychological burden, a full low FODMAP diet may be recommended. In people with considerable coexisting psychological symptoms, a Mediterranean diet should be considered (in addition to psychological strategies such as cognitive behavioural therapy or gut-directed hypnotherapy). In people with moderate levels of both gut and psychological symptoms a combined approach could be used. We also recommend avoiding the promotion of restrictive diets in people with an already very restricted diet, unintentional weight loss, severe mental illness or eating pathology.

Additional take-home messages for care of people with IBS and comorbid mental ill-health

Key take-home messages for clinicians for the safe and effective care of IBS with comorbid mental ill-health are presented in our article here. In addition to specific medical, psychological and dietary treatment recommendations we also guide on service delivery and training:

• Counselling should be patient-centred and trauma-informed.
• Provide adequate education on gut–brain interaction. Manage the language used to be psychologically safe and validate that gastrointestinal and psychological symptoms are real and taken seriously.
• Build rapport, be flexible and adjust frequency, duration and intensity of appointments as needed or desired by the person.
• Where possible, engage a multidisciplinary team to ensure the person is treated holistically.
• Understand thresholds for referral to other specialists (gastroenterologists, dietitians, gastropsychologists) — we provide specific guidance here.
• Understand the difference between psychological therapies specific for mental ill-health and those specific for treating IBS symptoms.
• Engage in additional training to assist in enhancing self-management (eg, mindfulness-based approaches).

Dr Heidi Staudacher is an advanced accredited practising dietitian with expertise in the dietary management of individuals with gastrointestinal disorders.

Dr Scott Teasdale is a Senior Research Fellow with the Discipline of Psychiatry and Mental Health and Accredited Practising Dietitian. He holds a National Health and Medical Research Council Emerging Leader Fellowship focusing on reducing physical health comorbidities in people with serious mental illness.

Dr Antonina Mikocka-Walus is Professor of Health Psychology in the School of Psychology and the former Faculty of Health HDR Director. She is a psychologist with expertise in clinical health psychology, behavioural medicine and psychosomatic medicine.

The statements or opinions expressed in this article reflect the views of the authors and do not necessarily represent the official policy of the AMA, the MJA or InSight+ unless so stated. 

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