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Expert Critique
FROM THE ASCO Reading Room
The main types of FODMAPS are lactose (dairy products); fructose (vegetables, sweeteners, fruits and juices, high-fructose corn syrup); fructans (artichokes, asparagus, leaks, garlic, onions, wheat); galacto-oligosaccharides (GOS) (beans); and polyols (fruits with pits, peaches, cherries, some vegetables, cauliflower, snow peas, artificial sweeteners).
Research on low-FODMAP diets has shown that approximately 50% of patients with IBS will have symptom improvement by 1 to 2 months. It should be noted, however, that a low FODMAP diet is a restrictive diet, and not feasible to maintain on a long-term basis. After patients restrict various FODMAPS from their diet, they should begin to slowly reintroduce foods that contain FODMAPS to see what they may or may not be sensitive to.
At this point we do not know what the long-term consequences of such a restrictive diet are. Gluten-free diets have also been studied in patients with IBS and have shown some benefit. It is unclear if gluten itself is a trigger for pain in patients with IBS, or if by decreasing gluten, one is actually decreasing the burden of FODMAP, thus leading to decreased bacterial fermentation, gas, bloating, and abdominal pain.
Older therapies that have been used for IBS include fiber and probiotics. Psyllium is often used for patients with both diarrhea and constipation-predominant IBS. Psyllium is an insoluble fiber that helps bulk up stool and regulate bowel frequency; it is often first-line therapy for patients with either diarrhea or constipation.
Other recent therapies for IBS include IBgard (encapsulated delayed-release peppermint oil). This releases in the small bowel and causes smooth muscle relaxation which has been shown to reduce abdominal pain. Lastly there is little evidence to support the use or probiotics or prebiotics. However, in our practice we typically recommend a trial of probiotics in patients with IBS, given the low side-effect profile.
There has been a renaissance of interest in the role of diet in the pathogenesis and symptomology of irritable bowel syndrome (IBS) – the most common gastrointestinal ailment in the world and a heterogeneous condition that generates an estimated 3.65 million annual healthcare visits in the U.S. With nearly two-thirds of patients perceiving their symptoms to be , and the variable efficacy of pharmacologic therapies "there has been somewhat of a paradigm shift in looking to specialized diets for symptom relief in patients with IBS," wrote , of the Dartmouth-Hitchcock Medical Center in, Lebanon, N.H., and a colleague in a comprehensive evidence review in
Trials have studied the roles of food intolerance and hypersensitivity, as well as other mechanisms such as gut hormones and interactions with gut microbiota, the paper noted, but solid data on dietary strategies remain sparse. The most promising approach appears to be restriction diets low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP), although gluten-free regimens have also yielded some encouraging results.
"Although there is interest in gluten-free diets and the elimination of foods tied to allergies, by far the greatest evidence is related to the low-FODMAP diet," said , of the University of Michigan in Ann Arbor, in comments to 番茄社区.
Added , of Cedars-Sinai Medical Center in Los Angeles: "Evidence is mounting that low-FODMAP works for both IBS-diarrhea and IBS-constipation, because by restricting foods that ferment, it restricts the fuel for bloating." According to epidemiology studies, IBS-constipation accounts for about 30% of IBS.
Low-FODMAP Regimens
Encompassing a wide range of healthy but poorly digested and absorbed foods including grains, dairy, vegetables, legumes, and fruits, FODMAPs interact with colonic flora to cause fermentation, gas, distention, and pain. of hydrogen breath testing found that these compounds triggered bothersome GI symptoms in IBS patients and healthy controls alike.
A comprehensive list of FODMAPs and their recommended dietary alternatives was recently published in a New Zealand in Clinical and Experimental Gastroenterology.
In an abstract at this year's Digestive Disease Week from the first U.S. randomized controlled trial of low FODMAP, Chey and colleagues reported that in a cohort of 92 IBS patients, more of those assigned to a 4-week low-FODMAP diet had an improvement of more than 10 points in scores on a 100-point quality-of-life index for IBS-diarrhea than controls assigned to a common regimen of small, frequent meals and avoidance of IBS trigger foods (58% versus 24%, P=0.0032).
Abdominal pain and bloating scores and stool frequency also improved from baseline in the FODMAP arm of the study versus controls. In addition, sleep quality score was superior for those on the intervention diet compared with those on the control diet (6.33 versus 7.46, P=0.0336).
Other have also reported symptom improvement with low-FODMAP diets, although studies also found some benefit from and .
Experts caution, however, that the long-term health effects of the unbalanced low-FODMAP diet banning nutritious foods that may be heart-healthy and cancer-preventive are unknown. "Stringent FODMAP restriction is not recommended owing to risks of inadequate nutrient intake and potential adverse effects from altered gut microbiota," wrote , and colleagues from the University of Otago in Christchurch in the New Zealand evidence overview.
"The low-FODMAP diet can work acutely, but it may not be a long-term solution," said Pimentel, adding that one health drawback is excessive weight loss. "So most of the expert dietitians who implement the diet recommend it for a 1- or 2-month period [only] because of possible health consequences." New modifications of the diet in which gluten-containing foods are not restricted may make it easier to tolerate on a long-term basis.
Peppermint Oil
Pimentel noted that the peppermint oil supplement IBgard is drawing attention for its significant alleviation of IBS symptoms. L-menthol, the main constituent, has antispasmodic, anti-carminative, topical analgesic, anti-infective, and 5-HT3 receptor antagonism properties. "Mainly, [IBgard] reduces bacteria and relaxes muscle to improve IBS symptoms," he said.
Gluten-free Diet
Even for IBS patients who do not have celiac disease, some encouraging research has found gluten elimination to be beneficial. In of 41 patients, a 6-week gluten-free diet produced a response in 29 patients (71%), with a mean total decrease in the IBS Severity Score from 286 at baseline to 131 after 6 weeks (P<0.0001).
suggested that the IBS triggers may be the carbohydrate components (fructans and galacto-oligosaccharides) in wheat rather than the gluten, explaining the efficacy in nonceliac patients.
Standard Exclusion Diets
Although long recommended for GI conditions, the elimination of food items remains an unproven approach, Chey noted. of 17 heterogeneous randomized controlled trials of elimination diets in 1,568 IBS patients was unable to find sufficient solid data to perform a meta-analysis. Limited evidence and the unknown adverse effects of long-term food restriction led Shah's group to recommend against the routine use of strict exclusion diets in IBS.
Foods specifically linked to allergies may be more suitable targets for elimination, Chey added. "Australian researchers have reported a higher likelihood of atopic phenomena such as eczema and asthma in IBS patients, suggesting that a subset of patients likely have immune dysregulation or [disordered] immune activation."
Fiber
Regarding fiber, a and meta-analysis of 14 randomized controlled trials with 906 IBS patients found insoluble fiber such as psyllium to be somewhat superior to placebo for improving global IBS symptoms, with a relative risk of 0.86 (95% CI 0.80-0.94). Insoluble dietary fiber such as bran, however, conferred little clinical benefit (RR 0.90, 95% 0.79-1.03).
Probiotics/Synbiotics
The review by Shah and his colleague found insufficient evidence to recommend prebiotics or synbiotics in IBS. "Any benefit is likely specific to individual strains and individual patients," said Chey. "Even studies showing a potential benefit report only a marginal therapeutic benefit of 7% to 10%, which tells you there is likely a subgroup of patients who get better with probiotics compared with placebo, while the majority probably do not."
That ties into the heterogeneity of the condition, he added. "Everybody's microbiome and genetics are different. IBS is not just one disease."
The bottom line? "We think most of the excitement in terms of treatment will reside in [manipulating] the microbiome," said Pimentel. In the meantime, dietary trial and error may be the best approach. As Shah et al concluded: "There still exists no one-size-fits-all dietary intervention for patients with IBS."