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Can a Diet Low in FODMAPs Reduce IBS Symptoms in the Real World?

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In patients with irritable bowel syndrome (IBS), a real-world diet low in fermentable oligosaccharides, monosaccharides, disaccharides and polyols (FODMAPs) reduced symptoms compared with a sham diet, researchers report in the October issue of Gastroenterology. The study also showed that co-administration of the multistrain probiotic increased numbers of Bifidobacterium species and might be given to restore these bacteria to patients on a low-FODMAP diet.

Changes in relative abundance of selected bacterial genera according to 16S rRNA sequencing. (A) Change in relative abundance of Bifidobacteria for low FODMAP diet (LFD) vs sham diet (P = .0027) and probiotic vs placebo (P = .3549). (B) Change in relative abundance of Streptococcus species for low FODMAP diet vs sham diet (P = .1141) and probiotic vs placebo (P = .00017). (C) Change in relative abundance of Lactobacillus species for low FODMAP diet vs sham diet (P = .5782) and probiotic vs placebo (P = .9521) (Wilcoxon rank-sum test, FDR correction). The central line indicates the median, the box indicates the 25th and 75th percentiles and the whiskers indicate 1.5× interquartile range.

IBS is a functional gastrointestinal disorder; most patients believe their symptoms to be related to diet. Many patients with IBS are placed on a diet with reduced fermentable carbohydrates—a diet low in FODMAPs—because carbohydrates increase small intestinal water and colonic gas. Their dietary restriction has been investigated in a number of trials, with up to 70% of patients reporting reduced symptoms.

A previous placebo-controlled trial of patients with IBS found that a low-FODMAP diet reduced symptoms. However, in this study, all dietary components were provided to participants, so it is not clear if this diet is effective in a real-world setting.

Furthermore, the low-FODMAP diet alters some genera of the intestinal microbiota and has been reported to reduce specific microbes, such as bifidobacteria, in patients with IBS.

Heidi Maria Staudacher et al aimed to investigate the effects of a diet low in FODMAPs compared with a sham diet in patients with IBS, and determine the effects of a probiotic on diet-induced alterations in the microbiota.

They performed a 2×2 factorial trial of 104 patients with IBS. Patients were either given counselling to follow a sham diet or diet low in FODMAPs for 4 weeks, but not the actual foods. Patients also received a placebo or multistrain probiotic formulation, resulting in 4 groups (27 receiving sham diet/placebo, 26 receiving sham diet/probiotic, 24 receiving low-FODMAP diet/placebo, and 27 receiving low-FODMAP diet/probiotic).

The sham diet restricted a similar number of staple and non-staple foods as the low-FODMAP diet, so the diets had similar degrees of difficulty to follow. For example, suitable carbohydrates on the sham diet included fruits such as apples, bananas, and pears, whereas oranges, raspberries, and strawberries were not allowed; the sham diet allowed grains such as wheat, but not rice.

After 4 weeks, Staudacher et al found no significant interaction between the interventions in adequate relief of symptoms or Bifidobacterium species.

In the intention-to-treat analysis, a higher proportion of patients receiving the low-FODMAP diet had adequate symptom relief (57%) than in the sham diet group (38%), although the difference was not statistically significant.

In the per-protocol analysis, a significantly higher proportion of patients on the low-FODMAP diet had adequate symptom relief (61%) than in the sham diet group (39%).

The total mean IBS severity score was significantly lower for patients on the low-FODMAP diet (173 ± 95) than the sham diet (224 ± 89), but there was no significantly difference between patients given probiotic (207 ± 98) or placebo (192 ± 93).

Patients on the low-FODMAP diet had signifcantly lower subscores for days of pain and distension severity, but higher scores in evaluations of physical health, energy/fatigue, body image, social reaction, and relationships, compared to patients on the sham diet, indicating a better quality of life. There was no effect of probiotic on HRQOL compared with placebo.

Fecal samples were collected from all participants at baseline and after 4 weeks and analyzed by quantitative PCR. At the 4-week follow-up time point, the abundance of Bifidobacterium species was significantly lower in fecal samples from patients on the low-FODMAP diet (8.8 rRNA genes/g) than patients on the sham diet (9.2 rRNA genes/g), but significantly higher in patients given probiotic (9.1 rRNA genes/g) than patients given placebo (8.8 rRNA genes/g). There was no effect of the low-FODMAP diet on microbiota diversity in fecal samples.

16S rRNA sequencing confirmed the low-FODMAP diet led to a significant reduction in relative abundance of Bifidobacterium species between baseline and 4 weeks of follow up (1.70% vs 0.79%) that did not occur in sham group (1.57% vs 1.93%). So, there was a mean reduction in the low-FODMAP group of 0.91% compared a mean increase of 0.36% in patients on sham diets (see figure).

There was no significant difference in the change in relative abundance of Bifidobacterium species between baseline and the 4-week follow-up time point between the probiotic group (1.60% vs 1.50%) compared with the placebo group (1.68% vs 1.18%).

Staudacher et al conclude that a diet low in FODMAPs leads to adequate relief of gastrointestinal symptoms in about 60% of patients with IBS, compared to fewer than 40% of patients receiving sham dietary advice. Low-FODMAP dietary advice alone reduced inake of FODMAPs by patients, without altering energy or macronutrient intake. These findings indicate that the observed effects are likely the result of FODMAP restriction rather than changes in nutrient intake. Furthermore, this trial showed that the decrease in bifidobacteria from the low-FODMAP diet can be modified with probiotics.

In an editorial that accompanies the article, Peter R. Gibson and Rebecca E. Burgell write that the overall findings provide convincing evidence that the low-FODMAP diet is more efficacious than a sham diet in patients with IBS, and that these results should calm dissenters regarding the diet’s efficacy in real-world practice.

The complexity of and difficulty in adhering to a low-FODMAP diet has been considered a limitation to its implementation. However, in this study, Staudacher et al spent only 10 minutes teaching each patient the diet, with no explanation of how FODMAPs might induce of symptoms. Gibson and Burgell state that although this approach was less involved than that considered best dietetic practice, it is reassuring that so many patients reported adequate relief of symptoms. The diet seems to be easier to implement than previously thought.


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Kristine Novak

Kristine Novak

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About The Author:

Dr. Kristine Novak

Dr. Kristine Novak

Dr. Kristine Novak is a science writer and editor based in San Francisco. She has extensive experience covering gastroenterology, hepatology, immunology, oncology, clinical, and biotechnology research discoveries.

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