IBS is one of the most prevalent gastrointestinal conditions, affecting 7–21% of people globally. People with IBS experience abdominal pain with altered stool form or frequency, which can dramatically affect their quality of life. IBS is categorized into subtypes according to bowel habits:
IBS with constipation (IBS-C)
IBS with diarrhea (IBS-D)
Mixed IBS (IBS-M)
Unsubtyped IBS (IBS-U)
🔍 Digging Deeper: How is IBS diagnosed?
IBS is diagnosed with the Rome criteria. The first version of the Rome criteria (Rome I) was established in the 1980s. Rome has since been updated three times; the most recent update (Rome IV) was in 2016.
Diagnosing IBS with the Rome IV criteria necessitates recurrent abdominal pain for an average of at least one day per week for the previous three months, with symptom onset at least six months before diagnosis. In addition, recurrent abdominal pain must be associated with at least two of the following:
Change in stool frequency
Change in stool form
The efficacy of pharmacological treatments for people with IBS is modest, and most people report food-related symptoms. Fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPS) are poorly absorbed dietary carbohydrates associated with gastrointestinal symptoms due to their fermentability and influence on intestinal fluid retention. Following a low-FODMAP diet involves temporarily reducing and then gradually reintroducing FODMAPs. Is this strategy efficacious for IBS?
This meta-analysis of 10 randomized controlled trials assessed the efficacy of low-FODMAP diets in people with IBS. The included studies compared low-FODMAP diets to control diets (such as traditional IBS dietary advice, a high-FODMAP diet, or a usual diet), were at least 3 weeks in duration, and included 511 total participants. The authors meta-analyzed the following outcomes:
Global improvement of IBS symptoms, assessed as a dichotomous outcome (i.e., improvement or no improvement; the criteria varied between studies but all were focused on identifying “clinically meaningful” improvements)
IBS symptoms, assessed with the IBS Severity Scoring System (IBS-SSS) score
Sub-items on the IBS-SSS (pain intensity, pain frequency, abdominal distension, dissatisfaction with bowel habits, and interference with life in general)
Irritable bowel syndrome-related quality of life (IBS-QOL)
Scores on the hospital anxiety and depression scale (HADS)
Stool consistency and frequency scores
Participants following a low-FODMAP diet were 54% more likely to report global symptom improvement and reported greater improvements in overall IBS-SSS scores and the following IBS-SSS sub-items:
Interference with life in general
Dissatisfaction with bowel habits
Additionally, participants following a low-FODMAP diet reported improved stool consistency and a non-significant reduction in stool frequency than participants following control diets. When the authors assessed the data based on IBS subtype, the benefits for stool consistency and frequency were more consistent among participants with IBS-D.
There were no effects of low-FODMAP diets on IBS-QOL, anxiety scores, depression scores, or BMI.
The data quality was rated as moderate for IBS-SSS scores, stool consistency, and stool consistency and frequency for IBS-D. The data quality for all other outcomes was rated as “low” or “very low.”
The restriction phase of a low-FODMAP diet is temporary, followed by food challenge testing and reintroduction of well-tolerated FODMAPs. During the four to six-week restriction phase, high-FODMAP foods are reduced or replaced with low-FODMAP alternatives.
It’s prudent to track dietary habits and GI symptoms during the restriction phase. If there is no change in symptoms during the restriction period, it could indicate unintentional FODMAP intake, another food intolerance, or a non-diet mechanism underlying symptoms. If symptoms do not improve during the restriction phase, high-FODMAP foods should be reintroduced in amounts previously consumed to confirm the lack of response.
After the restriction phase, systematic reintroduction of moderate- and high-FODMAP foods begins. Individual tolerance to the FODMAP groups can be assessed through food-challenge testing. This is the process of ingesting progressively larger servings of specific foods over the course of three days and monitoring symptoms, with a two- to three-day rest period between tests.
Long-term adherence to a low-FODMAP diet is not recommended, because the lack of prebiotics can negatively affect the gut microbiome, and a low-FODMAP diet can be nutritionally inadequate.
The Big Picture: Five other meta-analyses have been published assessing low-FODMAP diets for IBS:
A 2015 meta-analysis, which included 6 RCTs and 16 non-randomized interventions, found that low-FODMAP diets improved IBS-SSS and IBS-QOL scores and reduced abdominal pain and bloating.
A July 2017 meta-analysis of 8 RCTs reported that low-FODMAP diets improved gastrointestinal symptoms, abdominal pain, and health-related quality of life, compared to various other diets.
An August 2017 analysis of 10 studies (5 RCTs, 2 non-randomized controlled trials, and 3 prospective studies) reported that both low-FODMAP diets and standard IBS dietary advice improved IBS-SSS scores, with a non-significantly greater improvement observed in participants following low-FODMAP diets.
Another August 2017 meta-analysis of 6 RCTs and 6 cohort studies reported that participants following low-FODMAP diets experienced a greater reduction in pain, bloating, and stool frequency than participants following a traditional IBS diet, with no effect on stool consistency. That analysis also found that low-FODMAP diets reduced abdominal pain and bloating more than high-FODMAP diets and that they reduced abdominal pain and bloating in cohort studies without a control group.
A 2018 meta-analysis of 7 RCTs reported that a low-FODMAP diet reduced global symptoms compared to various control diets.
Overall, the body of literature suggests that low-FODMAP diets can be efficacious in reducing symptoms of IBS. They should always be utilized under the guidance of a registered dietitian well-versed in low-FODMAP dietary regimens.
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