Gene Limits Effectiveness of Low-Carb Diet on IBS-D

Individuals with irritable bowel syndrome with diarrhea (IBS-D) who have hypomorphic sucrase-isomaltase gene variants are 3 to 4 times less likely to respond to a carbohydrate-limited diet than their counterparts who are free of the gene, according to a new study.

To determine whether a low FODMAP diet—one that limits fermentable oligo-, di-, mono-saccharides and polyols that are not absorbed well in the small intestine—is less effective in individuals with IBS who carry the hypomorphic sucrase-isomaltase variant, the researchers re-evaluated results from a previous study.

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The researchers of the original study had explored the effect of a low FODMAP diet in participants with IBS-D. For the new study, the researchers stratified for the genotype. In all, 46 participants with the hypomorphic sucrase-isomaltase gene variant were identified for the new analysis.

Overall, 52.2% of participants in the original study experienced adequate relief of their IBS-D symptoms, defined as an improvement in symptoms of 50% or more. However, participants who carried the hypomorphic sucrase-isomaltase variant had a significantly lower response rate than those without the gene (43.5% vs 60.9%).

The researchers also evaluated the genotype data of 39 participants who followed the modified National Institute for Health and Care Excellence dietary guidelines. With a response rate of 16.7%, those with 2 copies of the hypomorphic sucrase-isomaltase gene variant were less likely to experience relief through a low-carb diet than participants with 1 copy (42.1%) or no copies (56.1%)

The researchers observed a similar trend for abdominal pain reduction, but the difference was not statistically significant.

“While study limitations include small sample size and lack of mucosal disaccharidase measurements in patients, this may bear implications for the development of patient treatment stratification strategies in IBS,” the researchers concluded.

—Colleen Murphy

Reference:

Zheng T, Eswaran S, Photenhauer AL, et al. Reduced efficacy of low FODMAPs diet in patients with IBS-D carrying sucrase-isomaltase (SI) hypomorphic variants [published online January 18, 2019]. Gut. doi: 10.1136/gutjnl-2018-318036.