Reference
Nybacka S, Törnblom H, Josefsson A, et al. A low FODMAP diet plus traditional dietary advice versus a low-carbohydrate diet versus pharmacological treatment in irritable bowel syndrome (CARIBS): a single-centre, single-blind, randomised controlled trial. Lancet Gastroenterol Hepatol. 2024;9(6):507-520. doi:10.1016/S2468-1253(24)00045-1
Study Objective
To directly compare the efficacy of 3 different treatment options for irritable bowel syndrome (IBS):
- Low-FODMAP (low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet combined with traditional dietary advice for IBS (LFTD group);
- Low-carbohydrate, high protein and fat, fiber-optimized diet (low-carb group); and
- Pharmacological intervention targeting the predominant IBS symptoms; e.g. abdominal pain, constipation, or diarrhea (drug group).
This study is the first to directly compare dietary interventions with symptom-targeted pharmacological treatment for IBS management.
Key Takeaway
All 3 groups improved IBS symptom severity, but both diet groups improved symptoms more than the drug group. Therapeutic diets, including low-FODMAP and low-carbohydrate diets, are potentially excellent first-line treatments for patients with IBS. The low-carbohydrate diet may be preferable for patients who find the low-FODMAP diet challenging to follow.
Design
Single-center, single-blind, randomized controlled trial
Participants
The modified intention-to-treat population of this study included 294 adults (82% female, mean age 38 ± 13 years) with moderate-to-severe IBS (IBS-SSS score ≥175, Rome IV criteria), including all IBS subtypes (IBS-D, IBS-C, or IBS-M). The active intervention phase lasted for 4 weeks, and symptoms were tracked for an additional 6 months.
Exclusion criteria included significant comorbidities or food allergies, adherence to a restrictive diet, or prior treatment with any of the interventions studied.
Intervention
Participants were randomly assigned (1:1:1) to an active treatment group (the LFTD group [n=96], the low-carb group [n=97], or the drug group ]n=101]) for 4 weeks.
Both diet groups were advised on the diet by a nutritionist, given recipes consistent with their diet, and had weekly home delivery of the ingredients necessary to prepare the recipes. They were instructed to consume weight maintenance calorie content and not change their activity level.
- to eat at regular intervals;
- to avoid excessive coffee, alcohol, carbonated drinks, and fatty and spicy foods;
- to chew food thoroughly; and
- to sit down during meals.1
This diet consisted of 50% carbohydrate, 33% fat, and 17% protein, with fiber content of 29.3 g/day, and a mean total FODMAP intake of 3-4 g/day. After the 4-week active intervention, participants were taught how to challenge FODMAPs to assess individual tolerance and were encouraged to continue avoiding problem FODMAPs and continue the NICE traditional advice.
The low-carbohydrate diet consisted of 10% carbohydrates, 67% fat, and 23% protein, with mean fiber intake of 23.9 g/day. After the 4-week active intervention, this group was encouraged to continue with a low-carbohydrate diet.
Pharmacological treatment was administered by the study physician, at no cost, and participants were instructed not to alter their diet or exercise regimens during the intervention. After the 4-week active intervention, participants were offered personalized dietary counseling and the option to continue with their prescribed medication.
Study Parameters Assessed
Participants completed an IBS Symptom Severity Score (IBS-SSS) and Gastrointestinal Symptom Rating Scale for Irritable Bowel Syndrome (GSRS-IBS) at baseline, weeks 1-4, and at the 3- and 6-month follow-ups. Additional questionnaires assessed quality of life, mental health, stool quality, general health, and dietary intake through a food record.
Primary Outcome
The primary outcome was a 50-point or greater reduction in IBS symptom severity on the IBS-SSS at 4 weeks, compared to baseline. The IBS-SSS assesses symptoms in 5 domains: pain severity, pain frequency, bloating severity, bowel habit dissatisfaction, and interference with daily life. Each symptom is scored on a scale of 0-100.
Secondary outcomes included changes in GSRS-IBS scores from baseline to 4 weeks, changes in nutrient intake, changes in quality of life (IBS-QOL), changes in anxiety and depression (HADS), and changes in intestinal somatic symptoms (PHQ-12).
Key Findings
At the end of the 4-week active intervention period:
- IBS symptoms, as well as anxiety and depression, significantly improved (P<0.0001) in all 3 groups. Quality of life and non-gastrointestinal somatic symptoms improved in all groups, but the most improvement was seen in the LFTD group.
- 76% of the LFTD group, 71% of the low-carb group, and 58% of the drug group achieved a reduction of 50 or more points in IBS-SSS scores.
- 62% of the LFTD group, 58% of the low-carb group, and 39% of the medical treatment group achieved a reduction of 100 or more points in IBS-SSS scores
- Significant changes in stool consistency were observed with both diets but not with pharmaceutical treatment. The LFTD diet primarily reduced the frequency of loose stools (P<0.0001), while the low-carb diet primarily reduced the frequency of hard stools (P<0.0001).
By 6 months, both dietary intervention groups partially returned to their baseline diets. The LFTD group consumed significantly fewer polyols and a higher percentage of protein compared to baseline, with most reintroducing FODMAP foods. The low-carb group consumed significantly fewer carbohydrates, more protein and fat, and fewer FODMAPs, despite not being counseled to reduce FODMAPs.
Participants continuing pharmaceutical treatment after the 4-week intervention showed a greater reduction in IBS-SSS scores (166 ± 82) compared to those who did not continue the medication (260 ± 101). However, adding dietary counseling to the medication regimen did not result in a significant difference in symptom severity (P=0.33).
Subjects in both diet groups experienced greater reductions in bloating than those in the medication group, although no medications specifically targeting bloating were prescribed.
Transparency
The study received funding through grants from various Swedish public and private foundations and organizations involved in healthcare and research. These entities had no role in study design, data collection, data analysis, data interpretation, or writing of the report.
Limitations
During the study, patients in the diet groups received guidance from a dietitian, detailed meal plans, and home delivery of ingredients at no cost. Implementing restrictive diets can be tricky, and it’s hard to know how much this type of support helped patients improve. It’s also hard to blind dietary therapies, and this study only included participants with moderate-to-severe IBS symptoms. It’s unclear what type of dietary counseling patients in the drug group received, or how much if at all they continued with their drug therapy, but this is not excessively limiting, since this group’s outcomes were significantly inferior to diet therapy for several outcomes immediately following the end of the active intervention.
Practice Implications
Approximately 4% of adults around the world have IBS, and even more in North America.2,3 Patients with IBS experience recurrent abdominal pain and altered bowel movements. Bloating is not one of the formal diagnostic criteria,1 but it’s the second most common symptom reported by IBS patients4 and can be challenging to treat.
Patients and practitioners often use dietary interventions to address IBS symptoms.4 The low-FODMAP diet is a frequently prescribed diet for people with IBS, and can be quite effective,5 but real-world adherence is challenging for many patients. It involves a lot of knowledge or calculation of the amounts of FODMAPs in various foods, and rationing of portion sizes, which can be stressful and can limit dining out and other food-oriented socialization.
The low-carbohydrate diet evaluated in this study reduced IBS symptoms about as well as the low-FODMAP diet and seems to be more practical and manageable. Both diets were superior to standard-of-care drug therapies for IBS in almost all measured domains, including bloating.
It’s helpful to have another evidence-informed diet strategy in our toolkit, especially one that can help with bloating. This study reaffirms that the low-FODMAP diet works for IBS, at least as well as conventional therapies, and establishes that a low-carbohydrate diet is also superior to drug therapy and is about as effective as low-FODMAP. Recommending a low-carbohydrate diet to patients with IBS who find a low-FODMAP diet overwhelming is a viable option. A low-FODMAP may be more effective for IBS-D patients, and a low-carb diet may be more effective for IBS-C patients.
To implement a low-carbohydrate diet like this, clinicians can direct patients to limit carbohydrates to no more than 10% of their total caloric intake, include significant amounts of high-quality fats, aim for a 3:1 fat-to-protein ratio, and aim for at least 24 grams of fiber per day. For patients with the financial means, working with a personal chef or specialized food delivery service for an initial 4-week introduction period may reduce obstacles and support effective uptake.
Conflict of Interest Disclosure
The authors declare no conflict of interest.
