Low FODMAP Diet Improves Fatigue, Mental Health in IBS, Study Finds

A 12-week strict low FODMAP intervention may have significant impacts on coexisting symptoms of fatigue, anxiety, and depression in patients with irritable bowel syndrome (IBS), according to findings from a recent study.1

The open-label, single-center, 12-week dietary intervention study was conducted at Haukeland University Hospital in Bergen, Norway, and found that after the intervention, participants experienced improvements in fatigue, anxiety, and depression, and performed better on a test of attention than they did pre-intervention.1

“By using a longer intervention period than typical LFD studies and measuring emotional and cognitive domains in addition to GI symptoms, this study fills an important research gap and contributes new insight into the broader effects of dietary treatment in IBS,” Astri Lundervold, a professor of clinical neuropsychology at the University of Bergen, and colleagues wrote.1

Globally, it is estimated that 5-10% of the population has IBS. Given the complex and multifactorial pathophysiology of IBS, patients frequently experience coexisting symptoms associated with psychological distress in addition to their GI symptoms. While the low FODMAP diet has established benefits for improving GI symptoms in IBS, less is known about its impact on extraintestinal symptoms such as fatigue, anxiety, and depression.1,2

The Bergen Brain Gut study is an open-label, single-center, 12-week dietary intervention for patients with moderate or severe IBS-D and IBS-M. The study was conducted at Haukeland University Hospital from May 2019 to June 2021 and enrolled patients 18–65 years of age who fulfilled Rome IV criteria, had an IBS–Symptom Severity Score (IBS-SSS) > 175, and followed a normal diet for ≥3 weeks before inclusion.1

In the study, participants followed a 12-week strict low FODMAP diet guided by a registered dietitian. The procedure included 3 in-person consultations at baseline and weeks 4 and 12 as well as a single phone consultation at week 8. Investigators assessed dietary adherence by calculating FODMAP intake from 3-day dietary records at baseline and week 12.1

At baseline and postintervention, participants completed standardized questionnaires assessing symptoms of fatigue, anxiety, and depression and performed a computerized test of attention, including the Chalder Fatigue Scale (CFQ-11), the Hospital Anxiety and Depression Scale (HADS), and the third edition of the Connors’ continuous performance test (CPT-3).1

Additionally, IBS-SSS was used to assess GI symptom severity at baseline and week 12. Changes in scores were used to investigate its association with changes in symptoms of fatigue, anxiety, depression, and inattention.1

Of 60 participants with IBS assessed for the dietary intervention, 49 were enrolled in the 12-week strict low FODMAP diet and 36 completed it. Most of the participants were female, and all had moderate or severe IBS at baseline.1

Following the 12-week intervention, investigators observed a significant reduction in self-reported fatigue (P < .013, d = 0.8). At baseline, 68% of participants were classified as having fatigue, decreasing to 32% post-intervention.1

Participants also reported a reduction in self-reported symptoms of anxiety (P < .013) and depression (P = .018), both with medium effect sizes. At baseline, 50% of participants were defined as doubtful cases or cases of anxiety. Following the intervention, the number of doubtful cases and cases of anxiety decreased to 21%.1

Investigators noted participants demonstrated improved performance on the CPT-3 test from baseline to the 12 week follow-up, with results collectively showing improved attentional control, as the patients show more consistent, accurate, and stable performance across the assessment—all hallmarks of reduced inattention.1

Further analysis revealed no statistically significant associations between changes in core GI symptoms measured by IBS-SSS and changes in fatigue, anxiety, depression, and attention.1

“The observed multidomain improvement supports a system view on IBS that extends beyond GI symptoms and underscores the potential therapeutic value of nutritional interventions for addressing the cognitive and affective components of this disorder,” investigators concluded.1

References

1. Bjørkevoll SMG, Randulff Hillestad EM, Lied GA, et al. A 12-Week Strict Low FODMAP Diet Reduces the Severity Levels of Fatigue, Depression, Anxiety, and Inattention in Patients with Irritable Bowel Syndrome. Curr Dev Nutr. doi:10.1016/j.cdnut.2025.107483

2. International Foundation for Gastrointestinal Disorders. About IBS. Accessed July 16, 2025. https://aboutibs.org/what-is-ibs/facts-about-ibs/