Managing irritable bowel syndrome: The low-FODMAP diet
ABSTRACTA diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) has been found to significantly reduce symptoms of irritable bowel syndrome (IBS). The diet is best implemented in two phases: initial strict elimination of foods high in FODMAPs, then gradual reintroduction based on symptoms. Further study of this diet’s effect on intestinal microbiota is needed.
KEY POINTS
- In clinical trials, the low-FODMAP diet has been found to improve symptoms in up to 70% of patients with IBS.
- FODMAPs are poorly absorbed for a variety of reasons.
- High-FODMAP foods include wheat, onions, legumes, dairy products, and many fruits and vegetables.
- The diet initially involves strict elimination of foods high in FODMAPs, after which they are gradually reintroduced as tolerated.
- A low-FODMAP diet may have negative effects on the gut microbiome. Therefore, we should be cautious about recommending this diet in the long term.
- Probiotics have a beneficial effect in IBS and can be taken concurrently with the diet.
LOW-FODMAP DIET REDUCES SYMPTOMS
The low-FODMAP diet was inspired by the results of several studies that evaluated the role of dietary carbohydrates in inducing IBS symptoms and found improvement with their restriction.25,26
One study found that 74% of patients with IBS had less bloating, nausea, abdominal pain, and diarrhea when they restricted their intake of fructose and fructans.27
A prospective trial randomized 41 patients with IBS to 4 weeks of either a low-FODMAP diet or their habitual diet.28 The low-FODMAP diet resulted in greater improvement in overall IBS symptoms (P < .05) and stool frequency (P = .008). This study was limited by different habitual diets between patients and by lack of standardization of the low-FODMAP diet.
Halmos et al,29 in a randomized crossover trial, compared gastrointestinal symptoms in IBS patients over 3 weeks on a low-FODMAP diet vs a moderate-FODMAP (ie, regular) diet, as well as in healthy controls. Food was provided by the study and was matched for all nutrients. Up to 70% of the IBS patients had significantly lower overall symptom scores while on a low-FODMAP diet vs IBS patients on a regular diet (P < .001); bloating, abdominal pain, and flatulence were reduced. Symptoms were minimal and unaffected by either diet in the healthy controls.
A double-blind trial30 randomly assigned 25 patients with IBS who initially responded to a low-FODMAP diet to be challenged by a graduated dose of fructose alone, fructans alone, a combination of both, or glucose. The severity of overall and individual symptoms was markedly more reduced with glucose consumption than with the other carbohydrates: 70% of patients receiving fructose, 77% of those receiving fructans, and 79% of those receiving a mixture of both reported that their symptoms were not adequately controlled, compared with 14% of patients receiving glucose (P ≤ .002).30
Murray et al31 evaluated the gastrointestinal tract after a carbohydrate challenge consisting of 0.5 L of water containing 40 g of glucose, fructose, or inulin or a combination of 40 g of glucose and 40 g of fructose in 16 healthy volunteers. Magnetic resonance imaging was performed hourly for 5 hours to assess the volume of gastric contents, small-bowel water content, and colonic gas. Breath hydrogen was also measured, and symptoms were recorded after each imaging session.
Fructose significantly increased small-bowel water content compared with glucose (mean difference 28 L/min, P < .001), but combined glucose and fructose lessened the effect. Inulin had no significant effect on small-bowel water content (mean difference with glucose 2 L/min, P > .7) but led to the greatest production of colonic gas compared with glucose alone (mean difference 15 L/min, P < .05) and combined glucose and fructose (mean difference 12 L/min, P < .05). Inulin also produced the most breath hydrogen: 81% of participants had a rise after drinking inulin compared with 50% after drinking fructose. Glucose did not affect breath hydrogen concentrations, and combined glucose and fructose significantly reduced the concentration measured vs fructose alone. In patients who reported “gas” symptoms, a correlation was observed between the volume of gas in the colon and gas symptoms (r = 0.59, P < .0001).31
The authors concluded31 that long-chain carbohydrates such as inulin have a greater effect on colonic gas production and little effect on small-bowel water content, whereas small-chain FODMAPs such as fructose are likely to cause luminal distention in both the small and large intestines. The study also showed that combining equal amounts of glucose and fructose reduces malabsorption of fructose in the small bowel and reduces the effect of fructose on small-bowel water content and breath hydrogen concentration.31
PROBIOTICS HELP
A Danish study32 randomized 123 patients with IBS to one of three treatments: a low-FODMAP diet, a normal diet with probiotics containing the strain Lactobacillus rhamnosus GG (two capsules daily), or no special intervention. Symptoms were recorded weekly. IBS severity scores at week 6 were lower in patients on either the low-FODMAP diet or probiotics compared with the control group (P < .01). Subgroup analysis determined that patients with primarily diarrheal symptoms were more likely to have improved quality of life with the low-FODMAP diet.
A LOW-FODMAP DIET MAY ALSO HELP IN INFLAMMATORY BOWEL DISEASE
The low-FODMAP diet has also been studied in patients with inflammatory bowel disease with functional gut symptoms. In a retrospective pilot study,33 overall symptoms improved in about half of such patients on a low-FODMAP diet. A controlled dietary intervention trial is needed to confirm these findings and define the role of the low-FODMAP approach for patients with inflammatory bowel disease.
Marsh et al34 performed a meta-analysis of six randomized clinical trials and 16 nonrandomized interventions of a low-FODMAP diet on improving functional gastrointestinal symptoms in patients with either IBS or inflammatory bowel disease. They found significant improvements in:
- IBS Symptoms Severity Scores in the randomized trials (odds ratio [OR] 0.44, 95% CI 0.25–0.76)
- IBS Symptoms Severity Scores in the nonrandomized interventions (OR 0.03, 95% CI 0.01–0.2)
- IBS Quality of Life scores in the randomized trials (OR 1.84, 95% CI 1.12–3.03)
- IBS Quality of Life scores in the nonrandomized interventions (OR 3.18, 95% CI 1.6–6.31)
- Overall symptom severity in the randomized trials (OR 1.81, 95% CI 1.11–2.95).
DIETARY COUNSELING IS RECOMMENDED
Adherence is a major factor in the success of the low-FODMAP diet in IBS management and is strongly correlated with improved symptoms.35 Patients should be counseled on the role of food in inducing their symptoms. Haphazard dietary advice can be detrimental to outcomes, as many diets restrict food groups, impairing the consumption of essential nutrients.36 The involvement of a knowledgeable dietitian is helpful, as physicians may lack sufficient training in dietary skills and knowledge of food composition.
Access to and cost of dietary counseling can be prohibitive for some patients. Group consultation, which can decrease costs to each patient, has been found to be as effective as one-on-one sessions when administering the low-FODMAP diet in functional bowel disorders.37
ELIMINATION, THEN REINTRODUCTION
Before embarking on the low-FODMAP diet, the patient’s interest in making dietary changes should be explored, a dietary history taken, and unusual food choices or dietary behaviors assessed. The patient’s ability to adopt a restricted diet should also be gauged.
The diet should be implemented in two phases. The initial phase involves strict elimination of foods high in FODMAPs, usually over 6 to 8 weeks.38 Symptom control should be assessed: failure to control symptoms requires assessment of adherence.
If symptoms are successfully controlled, then the second phase should begin with the aim of following a less-restricted version of the diet as tolerated. Foods should gradually be phased back in and symptoms monitored. This approach minimizes unnecessary dietary restriction and ensures that a maximum variety in the diet is achieved while maintaining adequate symptom control.39
LOW-FODMAP DIET ALTERS THE GUT MICROBIOTA
Multiple putative benefits of certain bacterial species for colonic health have been reported, including the production of short-chain fatty acids. Colonic luminal concentrations of short-chain fatty acids may be important to gut health, given their role in intestinal secretion, absorption, motility, and epithelial cell structure. Because short-chain fatty acids are products of bacterial fermentation, a change in the delivery of fermentable substrates to the colon would be expected to alter the concentrations and output of fecal short-chain fatty acids.18
Several studies evaluated the effect of the low-FODMAP diet on intestinal microbiota, finding a change in the bacterial profile in the stool of patients who adopt this diet. Staudacher et al28 found a marked reduction in luminal bifidobacteria concentration after 4 weeks of a low-FODMAP diet in patients with IBS.
A single-blind randomized crossover trial40 investigated the effects of a low-FODMAP diet vs a carefully matched typical Australian diet in 27 patients with IBS and 6 healthy controls. Marked differences in absolute and relative bacterial abundance and diversity were found between the diets, but not in short-chain fatty acids or gut transit time. Compared with fecal microbiota on the typical diet, low FODMAP intake was associated with reduced absolute abundance of bacteria, and the typical FODMAP diet had evidence of stimulation of the growth of bacterial groups with putative health benefits.
The authors concluded40 that the functional significance and health implications of such changes are reasons for caution when reducing FODMAP intake in the long term and recommended liberalizing FODMAP restriction to the level of adequate symptom control in IBS patients. The study also recommended that people without symptoms not go on the low-FODMAP diet.40
Molecular approaches to characterize the gut microbiota are also being explored in an effort to identify its association with diet.
The sustainability of changes in gut microbiota and the potential long-term impact on health of following a low-FODMAP diet require further evaluation. In the meantime, patients following this diet should have FODMAP foods reintroduced based on tolerance and should consider taking probiotic supplements.41
DIETARY ADEQUACY OF THE LOW-FODMAP DIET
Continual dietary counseling should minimize nutritional inadequacies and ensure that FODMAPS are restricted only enough to control symptoms. Because no single food group is completely eliminated in this diet, patients are unlikely to experience inadequate nutrition.
Ledochowski et al26 found that in the initial, strict phase of the diet, total intake of carbohydrates (eg, starches, sugars) was reduced but intake of total energy, protein, fat, and nonstarch polysaccharides was not affected. Calcium intake was reduced in those following a low-FODMAP diet for 4 weeks.
The diet can also reduce total fiber intake and subsequently worsen constipation-predominant IBS. For those patients, lightly fermented high-fiber alternatives like oat and rice bran can be used.
ACCUMULATING EVIDENCE
The low-FODMAP diet is accumulating quality evidence for its effectiveness in controlling the functional gastrointestinal symptoms in patients with IBS. It can be difficult to adhere to over the long term due to its restrictiveness, and it is important to gradually liberalize the diet while tailoring it to the individual patient and monitoring symptoms. Further clinical trials are needed to evaluate this diet in different IBS subtypes and other gastrointestinal disorders, while defining its nutritional adequacy and effects on the intestinal microbiota profile.
