Nutrient Intake, Diet Quality, and Diet Diversity in Irritable Bowel Syndrome and the Impact of the Low FODMAP Diet

Background: Individuals with irritable bowel syndrome (IBS) may modify their diet, which may pose nutritional risk. Further, some dietary approaches, such as a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs), are restrictive and may contribute to nutritional inadequacy.

Objective: Our aim was to evaluate habitual nutrient intake, diet quality, and diversity in IBS and the effect of a 4-week low FODMAP diet on these parameters compared with controls.

Design: Data from two randomized controlled trials were included for this secondary analysis. Participants were randomized to low FODMAP diet (n=63) or control diet (sham diet n=48, habitual diet n=19).

Participants/setting: Participants included 130 individuals with IBS referred to a tertiary center in London, UK between January 2010 to June 2011 and January 2013 to November 2014.

Intervention: Participants in one trial were randomized to receive either low FODMAP dietary counseling or sham control dietary counseling. In the other, they were randomized to receive low FODMAP dietary counseling or to continue habitual diet. All advice was provided by a specialist dietitian.

Main outcome measures: Habitual (usual) dietary intake at baseline (n=130) and after a 4-week intervention period was measured using 7-day food records.

Statistical analyses performed: Analysis of covariance and χ² tests evaluated differences across groups at 4 weeks.

Results: When examining habitual intake of individuals with IBS, fiber intake was low, with only 6 (5%) achieving the target (30 g/day). In those receiving low FODMAP advice, there was no difference in intake of most nutrients compared with controls. However, there was lower intake of starch (109 g/day) vs habitual control diet (128 g/day; P=0.030), and higher intake of vitamin B-12 (6.1 μg/day) vs habitual (3.9 μg/day) and sham control diets (4.7 μg/day; P<0.01). Overall scores for diet quality were lower after low FODMAP advice vs habitual control diet (P<0.01).

Conclusion: This study demonstrates many individuals with IBS fail to meet dietary reference values for multiple nutrients. A 4-week low FODMAP diet, when delivered by a specialist dietitian, does not impact on intake of most nutrients or diet diversity but decreases diet quality compared with control diets.