Written by: Emmanuel Dubure & Kristen DiFilippo, PhD, RDN
Introduction
Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder characterized by recurrent abdominal pain and changes in bowel habits involving diarrhea, constipation, or both. These symptoms may occur without visible signs of structural damage or disease in the digestive tract (National Institute of Diabetes and Digestive and Kidney Diseases, 2024). IBS is one of the most common gastrointestinal disorders in the United States, affecting an estimated 10%–15% of adults. Despite its high prevalence, many individuals remain undiagnosed, with only 5–7% of U.S. adults having received an IBS diagnosis. IBS is also one of the leading reasons for visits to gastroenterologists and contributes substantially to the healthcare burden (American College of Gastroenterology, 2026).
The exact mechanism underlying IBS is not fully understood (Black & Ford, 2020). However, it is widely connected to disordered communication between the gut and the brain, gut microbiome changes, and immune activation, leading to motility disturbances and visceral hypersensitivity (Ford et al., 2020; Jayasinghe et al., 2024). Because diet is a common trigger for symptoms, medical nutrition therapy is an important component of IBS management and plays an important role in managing symptoms and improving patients’ quality of life (Whelan et al., 2024).
The role of medical nutrition therapy in IBS management
Medical nutrition therapy (MNT) plays a significant role in the management of IBS symptoms. Dietary modification is considered a first-line treatment because certain foods can trigger or worsen gastrointestinal symptoms (Jayasinghe et al., 2024). Evidence-based approaches such as the low-FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet, fiber modification, and regular meal planning have been shown to reduce IBS symptoms and improve quality of life (Chey et al., 2022; Jayasinghe et al., 2024; Lacy et al., 2021). Therefore, MNT is an important component of comprehensive IBS management. Through individualized nutrition assessment and counseling, registered dietitians can help patients identify dietary triggers, control symptoms, and enhance overall nutritional status (Chey et al., 2022).
The primary goal of MNT is to reduce gastrointestinal symptoms while maintaining adequate nutritional intake and(Lacy et al., 2021). Quality of life in IBS reflects the broader impact of the disorder beyond gastrointestinal symptoms alone, including effects on physical functioning, mental and emotional well-being, and daily activities (AlDosari et al., 2024; Ballou et al., 2019).Current U.S. guidelines recommend an individualized, stepwise approach to the nutritional management of IBS, recognizing that no single diet is effective for all patients (Lacy et al., 2021).
Initial management focuses on assessing dietary habits, identifying symptom-triggering foods, encouraging regular meals, and promoting a balanced diet (Lacy et al., 2021). Soluble dietary fiber is recommended to improve symptoms in patients with IBS, particularly when constipation is present (Lacy et al., 2021). Research suggests that soluble fiber, which is found in sources such as oat bran, barley, beans, and psyllium, is more helpful in relieving IBS symptoms and can benefit patients with constipation-predominant IBS (Bijkerk et al., 2009; Lacy et al., 2021; Nagarajan et al., 2015). On the other hand, insoluble fiber, such as wheat bran, is less beneficial (Nagarajan et al., 2015) and generally not recommended as it may exacerbate abdominal pain and bloating (Currò, 2022; Lacy et al., 2021).
Low-FODMAP diets are recommended for improving global IBS symptoms, particularly abdominal pain, bloating, and diarrhea (Chey et al., 2022). Research indicates that FODMAPs increase small intestinal water content through their osmotic activity and undergo rapid fermentation by colonic bacteria, producing gases and short-chain fatty acids (SCFAs). Increased luminal water and gas production contribute to intestinal distension, which can trigger meal-related symptoms such as abdominal pain, bloating, and altered bowel habits (Moayyedi et al., 2020; Staudacher et al., 2014; Barrett & Gibson, 2012).
Current guidelines recommend that the low-FODMAP diet be implemented as a three-phase process. Phase 1 consists of short-term restriction (2–6 weeks) where FODMAP-containing foods are removed from the diet. In phase 2, individual FODMAP groups (i.e., fructans, lactose, galacto-oligosaccharides, and polyols) are systematically reintroduced while monitoring for symptoms to identify which groups trigger symptoms. Phase 3 involves personalizing the patient’s diet for the long term by limiting foods that trigger symptoms while maintaining the least restrictive diet possible(Chey et al., 2022). Strict long-term is discouraged as it may reduce dietary quality and adversely affect the gut microbiota (Halmos et al., 2014; Lacy et al., 2021). Importantly, the low-FODMAP elimination phase is not intended to restrict caloric intake. Individuals following the diet should continue to consume adequate calories to meet their energy and metabolic needs. Because the low-FODMAP diet involves dietary restriction, clinicians should assess for disordered eating behaviors and monitor for excessive restriction or difficulty with food reintroduction. Patients exhibiting concerns related to food avoidance, anxiety around eating, or inability to liberalize their diet may benefit from referral to an eating disorder dietitian or mental health professional (Whelan et al., 2024). Additionally, behavioral approaches targeting the gut-brain interaction, including gut-directed hypnotherapy, may be considered as adjunctive therapies for IBS symptom management (Simicich et al., 2024).There is currently insufficient evidence supporting the routine use of gluten-free diets, probiotics, or IgG-based food sensitivity testing for all patients with IBS (Biesiekierski et al., 2013; Ford et al., 2018; Lacy et al., 2021). While some patients may benefit from these interventions, current clinical guidelines do not recommend their routine use in the management of IBS (Lacy et al., 2021). Therefore, the American College of Gastroenterology recommends serologic screening for celiac disease in patients with diarrhea-predominant IBS or mixed-type IBS before initiating a gluten-free diet to avoid masking the diagnosis of celiac disease (Lacy et al., 2021).
Individuals with IBS may be at risk of malnutrition due to inadequate dietary intake (Bek et al., 2022). Therefore, nutrition assessment should also evaluate the potential for micronutrient deficiencies, particularly in individuals with restrictive eating patterns, poor dietary intake, or other risk factors for malnutrition. Assessment of biomarkers such as a complete blood count, iron studies, vitamin B12, and vitamin D may be appropriate when clinical findings or dietary history suggest possible deficiencies. When deficiencies are identified, individualized interventions should include dietary counseling to increase intake of nutrient-rich foods and, when appropriate, supplementation with nutrients such as vitamin D, vitamin B12, or iron in collaboration with the patient’s primary care provider or other qualified healthcare professionals (Raymond & Morrow, 2020).
[Alternatively: Individuals with IBS may be at risk of malnutrition due to inadequate dietary intake (Bek et al., 2022). Therefore, nutritional assessment in IBS should also evaluate the risk of micronutrient deficiencies, particularly in individuals with restrictive eating patterns, eating disorders, or other risk factors for malnutrition. When the nutrition assessment or clinical presentation suggests possible micronutrient deficiencies, appropriate laboratory evaluation and management should be considered in collaboration with the patient’s primary care provider or other qualified healthcare professional (Chey et al., 2022).]
Overall, current guidelines emphasize personalized dietary management, beginning with general healthy eating recommendations and progressing to evidence-based interventions, such as treatment with soluble fiber and a structured low-FODMAP diet.
Counseling tips for medical nutrition therapy for IBS
Effective nutrition counseling is an important component of helping individuals with IBS successfully manage their symptoms and maintain adequate nutritional status. Counseling should begin with a comprehensive nutrition assessment, including a review of the patient’s dietary intake, symptom history, lifestyle habits, medications, and psychosocial factors. Nutrition counseling can help patients adopt dietary changes while maintaining nutritional adequacy and quality of life (Chey et al., 2022; Lacy et al., 2021). Important counseling strategies include:
- Perform a comprehensive nutrition assessment before recommending dietary changes.
- Encourage patients to keep a food and symptom diary to identify individual triggers.
- Explain that IBS trigger foods vary among individuals and unnecessary long-term food restrictions should be avoided.
- Educate patients that the low-FODMAP diet has three phases (elimination, reintroduction, and personalization) and should ideally be implemented under the guidance of a registered dietitian.
- Encourage regular meals, adequate fluid intake, and gradual increases in soluble fiber when appropriate.
- Assess lifestyle and environmental factors, including stress, sleep, and physical activity, discuss their potential impact on IBS symptoms, and provide individualized counseling to support sustainable lifestyle changes.
- Schedule follow-up visits to monitor symptoms, assess nutritional status, reinforce education, and adjust the nutrition plan as needed.
(Chey et al., 2022; Lacy et al., 2021)
Conclusion
Irritable bowel syndrome (IBS) is a common chronic gastrointestinal disorder that can significantly affect an individual’s quality of life. Evidence-based medical nutrition therapy (MNT) is a fundamental part of symptom management. Individualized dietary interventions, including the low-FODMAP diet, appropriate fiber modification, regular meal patterns, and identification of personal food triggers, have been shown to reduce symptoms and improve overall well-being. Nutrition counseling provided by a registered dietitian plays an important role in helping patients implement these strategies while maintaining adequate nutritional intake. By combining these approaches with lifestyle modifications and ongoing follow-up, healthcare providers can help individuals with IBS better manage their symptoms and improve their long-term quality of life.
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