A Mediterranean diet could be beneficial for irritable bowel syndrome Original paper

In this 6-week randomized controlled trial, adopting a Mediterranean diet led to improvements in irritable bowel syndrome symptoms. The diet did not involve a change in the participants’ fiber or FODMAP intake.

The effect of a Mediterranean diet intervention in participants with irritable bowel syndrome (IBS).

The primary outcomes were the feasibility and acceptability of a Mediterranean diet among people with IBS. The secondary outcomes included IBS symptoms and mental health indices.

59 people (average age of 34; 49 women and 10 men) with IBS who were living in Australia.

All participants had a Rome IV diagnosis of IBS and experienced abdominal pain at least twice per week but did not have any other gastrointestinal conditions or eating disorders. Additionally, the participants had mild or moderate anxiety or depressive symptoms, based on a score of 8–14 on the Hospital Anxiety and Depression Score (HADS) subscale.

In this 6-week randomized controlled trial, the participants were assigned to follow a Mediterranean diet or their usual diet. The participants assigned to the Mediterranean diet received dietary counseling via a 20–minute to 30-minute virtual session with a dietitian. Details on the Mediterranean diet intervention can be found in the “Anything else I need to know?” section at the end of this summary.

Some components of the Mediterranean diet can be IBS triggers, such as onions, garlic, and legumes. Participants were advised to introduce these foods slowly and exclude them when appropriate.

Diet feasibility was defined as an increase of 2 points on the Mediterranean Diet Adherence Screener (MEDAS), which measures level of adherence to the diet. Diet acceptability was based on a questionnaire in which participants rated the diet out of 5 points, with more than 3 considered acceptable. IBS symptoms were assessed using the IBS Severity Scoring System (IBS-SSS). The HADS questionnaire was used to assess symptoms of depression and anxiety.

The Mediterranean diet was considered feasible for people with IBS, as the group assigned to the diet increased their MEDAS score by an average of 2.1 points compared to the baseline. The participants in the control group increased their MEDAS score by an average of 0.5 points. The Mediterranean diet was also considered acceptable, as the participants assigned to the diet rated its acceptability as 4.3 out of 5.

IBS symptom severity improved in the diet group compared to the control group (change in IBS-SSS scores: –113 vs. –20). This improvement was considered clinically significant.

Effect of a Mediterranean diet on IBS symptom severity

Symptoms of both depression and anxiety decreased in the Mediterranean diet group compared to the control group.

The two groups consumed similar amounts of FODMAPs, fiber, and calories.

IBS is a common gastrointestinal (GI) disorder featuring symptoms like abdominal pain, bloating, nausea, diarrhea, and constipation. Diet often plays a central role in the management of IBS, with one of the most common approaches being a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs). FODMAPs are a class of carbohydrates in food that can provoke gastrointestinal symptoms by promoting gas production and fluid retention in the gut. A large number of foods contain appreciable amounts of FODMAPs, including many fruits, vegetables, grains, beans, and nuts.

A low-FODMAP diet has been repeatedly found to improve IBS symptoms.^[1] However, the diet is not without downsides. It can be difficult to follow due to its complexity and numerous restricted foods. It’s also not recommended that people follow the diet over the long term, due to potentially deleterious changes in nutrient intake. Finally, some people do not experience adequate symptom resolution from the diet.

This is what makes the current trial somewhat novel and exciting — it suggests that a Mediterranean diet is a viable approach to improving IBS symptoms and that the benefits are independent of FODMAP restriction because FODMAP intake was not different between study groups.

A Mediterranean diet also has a good track record when it comes to health outcomes. It’s one of the most well-studied dietary patterns, having been shown to lower the risk of cardiovascular disease. Following the diet more closely is also associated with a lower risk of Alzheimer’s disease,^[2] frailty, and certain types of cancer.^[3] The diet has even been found to improve symptoms of depression in a few clinical trials, a finding seen in the current study as well.^[4][5][6] In short, rather than requiring people to strike a balance between managing IBS symptoms and eating a healthful diet, a Mediterranean diet seems to offer the best of both worlds.

Exactly how a Mediterranean diet helps with IBS remains far from certain. One speculative possibility is that the effect is caused by polyphenols and other related molecules supplied by the diet. Human evidence remains limited, but some researchers have hypothesized that polyphenols might be beneficial for IBS, possibly via anti-inflammatory, immune-modulating, and/or microbiota-mediated effects.^[7]

Ellagic acid is a polyphenol found in plant foods, including various berries and nuts, foods that are encouraged on a Mediterranean diet. In a 2-month randomized controlled trial from 2021, supplementation with ellagic acid reduced IBS symptoms compared to a placebo.^[8] Another source of polyphenols is olive oil, a key component of the Mediterranean diet (the current study recommended about 2 ounces per day). Although no studies have tested the effect of olive oil on IBS, one randomized crossover trial in people with ulcerative colitis, a type of inflammatory bowel disease, found that using extra virgin olive oil, which is high in polyphenols, improved gastrointestinal symptoms compared to using canola oil, which is low in polyphenols.^[9]

Finally, it should be acknowledged that at least some of the effects seen in the current study came from a placebo effect, with benefits arising from participants’ expectation that a Mediterranean diet would be beneficial. It’s well established that the brain and nervous system play an important role in the pathophysiology of IBS,^[10] meaning that a psychological change can probably lead to improvements in GI symptoms among people with IBS.^[11] The degree of improvement in IBS symptoms in the current trial appears similar to that of previously conducted trials that tested the effect of a low-FODMAP diet,^[1][12] thus strengthening the idea that a Mediterranean diet does provide true benefits for IBS.

The Mediterranean diet used in this study emphasized whole grains, vegetables, fruit, legumes, nuts, olive oil, dairy, and seafood, included moderate poultry, and limited refined sugar, butter, and processed meat. The diet also included a single serving of red meat per week and allowed a small amount of red wine for alcohol drinkers. The participants were advised to cook using gentler cooking methods, favoring stewing and boiling and avoiding frying or barbecuing. To assist with diet compliance, at the start of the trial participants in the Mediterranean diet group were provided with the following foods:

• 1 loaf of seeded sourdough bread
• 750 grams of oats
• 500 mL of extra virgin olive oil
• 180 grams of tuna in oil
• 12 grams of mixed dried herbs
• 450 grams of almonds
• 500 grams of peanut butter
• 250 grams of frozen salmon filets
• 800 grams of tinned tomatoes
• 800 grams of tinned chickpeas
• 400 grams of tinned 4-bean mix
• 1 brown onion
• 180 grams of mixed salad leaves
• 500 grams of frozen mixed berries
• 1,000 grams of Greek yogurt