Is a Low-FODMAP Diet the Next Big Thing?

Does the Evidence Support Efficacy?

In reviewing the spate of studies extolling the benefits of a low-FODMAP diet in patients with IBS, there is a noticeable lack of uniformity. The studies suffer from varying definitions of clinical response, inclusion of patients without clearly stratifying them by Rome criteria–based IBS subtypes, disparity in the symptom questionnaires employed, low sample sizes, short diet durations, and variable rigor in diet restriction and implementation (eg, some provide all the food, others a dietitian-led educational approach). Feeding studies are difficult to "blind" if the diet components are included as whole foods.^[18] It is unclear as to whether there is a dose-dependent response to FODMAPs reduction: greater outcome with better adherence. With such broad restriction, it is also unclear as to which prohibited food component was responsible for the favorable response in any individual patient.

With these caveats in mind, there are several key studies that demonstrate the reported effect of FODMAPs restriction on patients with IBS.

Eswaran and colleagues^[19] compared the efficacy of a low-FODMAP diet versus a diet based on the traditional modified National Institute for Health and Care Excellence (mNICE) guidelines for patients with IBS and diarrhea (IBS-D). The mNICE is a multifaceted approach that prescribes a high fluid intake, alcohol and caffeine restriction, and limited fiber intake. Over half (52%) of the low-FODMAP diet group versus 41% of the mNICE group reported adequate relief of their symptoms. Compared with baseline scores, the low-FODMAP diet led to a greater reduction in abdominal pain, bloating, consistency, frequency, and urgency than the mNICE diet.

In a separate study,^[20] this group compared the effects of the low-FODMAP diet with the traditional dietary recommendations on health-related quality of life (QOL), anxiety and depression, work productivity, and sleep quality in patients with IBS-D. After 4 weeks, a significantly higher proportion of patients in the low-FODMAP diet group had a meaningful clinical response, based on an increased IBS-QOL score, than subjects in the mNICE group (52% vs 21%). Of note, anxiety scores and activity impairment were significantly reduced in those adhering to the low-FODMAP diet compared with the mNICE diet.

Several other studies have achieved a similar outcome.^{[11,12,13,18,21,22,23,24,25,26,27]} In one prospective study, the efficacy of the low-FODMAP diet was durable over a follow-up period of approximately 16 months in 90 consecutively treated patients with IBS.^[28] A somewhat lower response rate was reported by Böhn and coworkers^[22] who compared the effects of a diet low in FODMAPs with traditional dietary advice. Patients with IBS were randomly assigned to either a diet low in FODMAPs or a dietary approach frequently recommended for patients with IBS (a regular meal pattern; avoidance of large meals; and reduced intake of fat, insoluble fibers, caffeine, and gas-producing foods, such as beans, cabbage, and onions). The severity of IBS symptoms was reduced in both groups during the intervention, without a significant difference between the groups. At the end of the 4-week diet period, 50% of the patients in the low-FODMAP diet group had reductions from baseline in the IBS Symptom Severity Score (IBS-SSS) of >50, the minimal change considered to be clinically relevant, compared with 46% of patients in the traditional IBS diet group.

Quality of the Data

Krogsgaard and colleagues^[29] systematically analyzed the quality of published trials on the symptomatic effects of the low-FODMAP diet for patients with IBS. Nine randomized controlled trials (RCTs) were eligible (542 patients). The authors found a high risk for bias in these RCTs; an absence of diets studied in a randomized, controlled setting for more than 6 weeks; and a lack of trials that examined the effect of reintroduction. They commented that the symptomatic effects reported in the trials could possibly be driven primarily by a placebo response.

A meta-analysis by Marsh and colleagues^[30] supported the efficacy of a low-FODMAP diet in the treatment of functional gastrointestinal symptoms. They suggest further research ensuring that studies include dietary adherence, include a greater number of patients, and assess the long-term adherence to a low-FODMAP diet.

In addition to the RCTs assessing a low-FODMAP diet, a published real-world experience with the low-FODMAP diet reported that approximately 70% of patients with IBS respond.^[18] This is significant because the monitored feeding studies do not reflect real-world conditions, where people must make their own food choices, with variable rigor and adherence.^[18]

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