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Two dietary interventions were more effective in reducing irritable bowel syndrome (IBS) symptom severity compared with pharmacotherapy, a randomized controlled trial showed.

After 4 weeks of treatment in the modified intention-to-treat population, 76% of participants following a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) and 71% of those following a low-carbohydrate diet had a reduction of 50 or more points in the IBS Severity Scoring System compared with 58% of those receiving optimized medical treatment (P=0.023), reported Sanna Nybacka, PhD, of the University of Gothenburg in Sweden, and colleagues.

"At 4 weeks, between-group comparisons showed significant differences in pain severity, pain frequency, bloating severity, and daily life interference, but not in bowel habit dissatisfaction," they wrote in .

The authors also noted that participants across all three groups experienced improved quality of life, anxiety and depression symptoms, and non-gastrointestinal somatic symptoms. Over 6 months of follow-up, the improvements largely persisted.

IBS affects an estimated 4% of adults, but it's been unclear how dietary interventions compare to pharmacotherapy in reducing symptoms, which most often include abdominal pain, constipation, and diarrhea.

"The key implication of this study is the potential of dietary interventions to become first-line treatments for IBS," noted Uday C. Ghoshal, MD, of Apollo Multispeciality Hospitals in Kolkata, India, and colleagues in an .

However, they pointed out that diets, though likely less expensive than medications, have their own limitations, including "nutritional compromise, gut microbiota effects, difficulty integrating into a vegetarian diet, development of avoidant restrictive food intake disorder, and social and psychological effects."

In addition, some patients may be hesitant to switch to alternative foods, cost may be a factor in changing diets for some patients, and those with cognitive impairment may struggle to change diets, they wrote, so it's important to determine who is best suited for a dietary intervention versus medication.

"Furthermore, if a patient's primary diet does not actually include trigger foods, placing them on a restrictive diet might be needless and ineffective," the editorialists added. "A dedicated dietitian should thoroughly assess the primary diet before the implementation of restrictive diets, and candidates suitable for pharmacotherapy should be identified."

For this conducted at a specialized outpatient clinic at the Sahlgrenska University Hospital from January 2017 to September 2021, Nybacka and colleagues compared three treatments in 294 adults with IBS over 4 weeks: 96 patients following a diet low in FODMAPs -- poorly digested short-chain carbohydrates that reduce the amount of fermentable substrates and water to the colon -- alongside traditional IBS dietary advice, 97 patients following a fiber-optimized diet low in total carbohydrates and high in protein and fat, and 101 patients receiving pharmacotherapy to target their dominant IBS symptom.

Most of the participants (82%) were women, mean age was 38, and all but eight had a body mass index between 18 and 35. All participants had moderate-to-severe symptom severity based on the IBS Severity Scoring System and did not have any other serious diseases or food allergies. Though 20 participants dropped out or were lost to follow-up during the study, the dropout rate did not significantly differ across groups.

All groups experienced a significant decrease in IBS Severity Scoring System score (P<0.0001), but the change was greatest in the low-FODMAPs diet group (-149 points, P<0.0001), followed by the low-carbohydrate diet group (-128 points, P=0.0004), and the medical treatment group (-76 points). When the researchers assessed treatment response based on a score reduction of at least 100 points, the response rates were 61% in the low-FODMAPs diet group, 58% in the low-carbohydrate diet group, and 39% in the medication group (P=0.0025).

Most participants completed the 4 weeks of treatment in each group (90-95%). Two patients in each of the diet groups said that adverse events were the reason for discontinuing their intervention. Five participants in the medical treatment group stopped treatment prematurely due to side effects. No serious adverse events or treatment-related deaths occurred.

At the conclusion of the 4-week intervention, participants in the medication group were offered personalized dietary counseling if they wanted it, and 74% accepted. The participants in the diet groups were encouraged to continue with those diets. The low-FODMAPs participants were also provided instruction on gradual reintroduction of FODMAPs based on how well they individually tolerated them.

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