The effect of low-FODMAP diet on patients with irritable bowel syndrome (2025)

Irritable bowel syndrome (IBS) is an inveterate and burdensome gastrointestinal disease characterized by abdominal pain associated with alteration of bowel habits. IBS is a common condition affecting 9–23% of the population, with a reported 80% being female, with effects on personal lifestyle and medical service cost¹. As outlined by Saha and supported by the Rome criteria, IBS is commonly classified into three subtypes based on stool patterns: constipation-predominant (IBS-C), diarrhea-predominant (IBS-D), and mixed-type (IBS-M)². Additionally, (IBS) has been found to have detrimental effects on various aspects of an individual’s well-being, including physical health, social and emotional functioning, dietary habits, sexual well-being, and overall quality of life³.

The adverse effects of (IBS) encompass recurring episodes of abdominal pain or bloating accompanied by either constipation or diarrhea. However, this condition may also manifest with additional symptoms beyond the gastrointestinal (GI) tract, such as increased urinary frequency, fatigue, lower back pain, headaches, dizziness, muscle aches, anxiety, and depression⁴.

The diagnostic criteria for irritable bowel syndrome are varied. One of the latest international studies for diagnosing IBS is the Rome IV criteria⁵. A significant number of IBS patients reported a worsening of their symptoms after eating⁶. The stages of treatment begin with lifestyle modification and nutritional intervention with certain types of diets, fibers, and probiotics⁵.

Recently, there has been an increased focus on the role of food in the management of functional symptoms associated with IBS. This resulted in an expanded understanding of the dietary interventions for IBS being developed⁶. According to Mullin and others, patients who have been diagnosed with IBS may experience adverse reactions and sensitivities to specific dietary components, including gluten, wheat, lactose, and fermentable sugars such as fructose malabsorption⁷. Therefore, individuals with IBS should regulate their dietary intake by consuming fiber, avoiding foods that trigger symptoms, and incorporating probiotics into their regimen⁸.

Studies have repeatedly demonstrated that certain categories of food have the potential to worsen IBS symptoms. These include wheat-based cereals, high-fat dairy products, spicy meals, coffee, alcohol, insufficient consumption of vegetables, legumes, and fruits, and irregular meal patterns. IBS patients may also demonstrate a heightened sensitivity to fermentable oligosaccharides, disaccharides, monosaccharides, polyols (FODMAPs), and gluten, hence exacerbating their symptoms. Consequently, recent studies have directed their attention to examining the efficacy of a low- FODMAP diet in mitigating symptoms⁹. FODMAPs are a group of fermentable carbohydrates, including oligosaccharides, disaccharides, monosaccharides, and polyols, exhibiting limited absorption in the human body. These compounds have the ability to interact with the microbial population residing in the small intestine, influencing the differentiation of intestinal stem cells and leading to a reduced production of endocrine cells. FODMAPs are prone to fermentation, resulting in the accumulation of fluid within the gastrointestinal system. This fermentation process also contributes to the generation of gas and the occurrence of bloating. Their osmotic activity draws water into the intestinal lumen, potentially resulting in diarrhea¹⁰. The sources of FODMAPs in the diet exhibit variability, encompassing grains, select fruits and vegetables, dairy products, and artificial sweeteners. By reducing the intake of fermentable components, the low-FODMAP diet decreases fermentation and osmotic load, alleviating gastrointestinal symptoms and improving the overall quality of life for IBS patients^5,10.

Multiple prior studies have indicated that the implementation of a low-FODMAP diet has been associated with enhanced quality of life for individuals diagnosed with (IBS), and a reduction in the intensity of their symptoms¹¹. However, in Saudi Arabia and the Middle East, formal national dietary guidelines for managing IBS are currently lacking. Despite this, the low-FODMAP approach is increasingly being adopted in clinical nutritional practices, particularly in urban healthcare settings. Developing region-specific dietary guidelines that align with local dietary patterns remains crucial for improving IBS care in this population. This study aimed to evaluate the impact of a low-FODMAP dietary intervention on IBS symptom severity in adults living in Jeddah, Saudi Arabia.

Study sample

This study involved a low-FODMAP dietary intervention program conducted with a sample of 45 adults (12 males and 33 females) diagnosed with Irritable Bowel Syndrome residing in Jeddah, Saudi Arabia, from March to July 2022. Participants were recruited from the Department of Family Medicine at King Abdulaziz University Hospital (KAUH) and the Primary Health Care Centers (PHCC) of King Fahd Hospital in Jeddah. Individuals were of both genders, ranged in age from 18 to 45 years, had a normal body mass index (BMI), and did not report the use of any drugs, antibiotics, or dietary supplements. The inclusion criteria were those who had received a medical diagnosis of moderate to severe irritable bowel syndrome, specifically those with IBS characterized by persistent diarrhea (IBS-D) or a combination of constipation and diarrhea (IBS-M), as determined by a healthcare professional employing the ROME III criteria. Exclusion criteria encompassed individuals presenting with additional chronic ailments, prior abdominal surgical interventions, comorbidities such as diabetes or inflammatory bowel disorders, as well as those below the age of 18 or over 45 years. Additionally, exclusion criteria included pregnant and lactating women, individuals who consume laxatives, herbal remedies, medications, and dietary supplements in order to alleviate symptoms associated with IBS, and individuals who are classified as obese or overweight. Participants were required to exhibit negative indicators of celiac disease.

Ethical approval

Ethical approval was obtained from the Research Ethics Committee of the Biomedical Ethics Unit of King Abdulaziz University, College of Medicine (No. HA-02-J-008). Also, approval was obtained from Jeddah Institutional Review Board (IRB), Ministry of Health. All methods were performed in accordance with relevant guidelines and regulations.

Study procedures

Study participants were randomly selected from outpatient departments of Family Medicine at King Abdulaziz University Hospital (KAUH) and the Primary Health Care Centers (PHCC) of King Fahd Hospital in Jeddah. Before commencing the interview and questionnaire, participants were provided with information regarding the aims of the study and provided their informed consent. Informed consent was obtained from all subjects and/or their legal guardian(s). A preliminary investigation was undertaken using a sample of 20 individuals diagnosed with IBS. Participants completed a demographic and symptom-related questionnaire, which included the Irritable Bowel Syndrome Symptom Severity Scale (IBS-SSS) to assess the severity of their symptoms. The objective of this pilot study was to assess the level of clarity in the language of the questionnaire. The data was collected through face-to-face interviews conducted in private screening rooms, of an average duration of 15–20min, during which standardized questionnaires were employed. Subsequently, the nurse proceeded to obtain anthropometric measurements, encompassing weight and height, within a designated screening area. The researcher then proceeded to calculate the Body Mass Index (BMI), classified as underweight < 18.5, normal weight 18.5–24.9, overweight 25.0-29.9, or obese > 30.0¹².

Study questionnaire

A questionnaire was administered to gather social and demographic information regarding gender, age, marital status, and economic status. Additionally, IBS symptoms were assessed using a modified version of the Rome III criteria. The choice to use Rome III was based on its broader diagnostic framework and its prevalent application in clinical settings during the study period within our region. Moreover, many of the participants had already been diagnosed using the Rome III criteria, making it a practical and appropriate tool for both recruitment and consistent symptom evaluation¹³. Symptom severity was further evaluated using the IBS Symptom Severity Scale (IBS-SSS), a validated measurement tool that assigns scores ranging from 0 to 500, with higher scores indicating more pronounced symptoms. Participants were categorized into three groups based on symptom severity: mild (75–175), moderate (175–300), or severe (> 300)¹⁴.

A validated semi-quantitative food frequency questionnaire was utilized to assess both FODMAP and nutrient consumption. This questionnaire, originally developed by Monash University, was translated from English to Arabic following a forward-backward translation process conducted by two independent bilingual translators to ensure accuracy and cultural relevance. A panel of experts in gastroenterology and nutrition then reviewed the translation. With permission from the Rome Foundation and Monash University, the Food Frequency Questionnaire (FFQ) was adapted to include locally available foods and beverages relevant to the dietary habits of the target population.

The Low- Low-FODMAP Dietary Intervention: Participants took part in a structured dietary intervention based on the low-FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) approach, which was designed to alleviate IBS symptoms by reducing the intake of fermentable carbohydrates. The sessions were conducted using the Zoom platform. A WhatsApp group was established to facilitate patient monitoring and follow-up. The use of a low-FODMAP diet can assist patients in making informed decisions regarding their daily dietary choices and in avoiding the consumption of items that are high in FODMAPs. The intervention was carried out in two phases over a total of 10 weeks: Restriction Phase (6 weeks): Participants followed a reduced FODMAP diet, eliminating high-FODMAP foods under guidance. Reintroduction Phase (4 weeks): Participants gradually reintroduced specific FODMAP groups to identify individual food triggers and tolerance levels.

All study materials, consent forms, dietary guidelines, and symptom assessment tools were provided in Arabic to ensure cultural and linguistic appropriateness. At the end of the 10-week program, IBS symptoms were reassessed using the same standardized questionnaire applied at baseline.

Statistical analysis

Statistical Package for Social Sciences (SPSS v.29) program was used. Descriptive statistics are used to describe the basic features of the data, and inferential statistics are used to test the difference between groups in the study, as follows: T-test was used to compare the nutrient intake of IBS patients before and after the intervention program. Mann–Whitney U test was used to compare consumed FODMAP according to IBS symptoms. The Chi-squared test was used to check the association between demographics (gender, age, and IBS symptoms) with the consumed FODMAP before and after the intervention program. P-values < 0.05 were considered statistically significant.

Table1 illustrates the demographic characteristics of the study participants, revealing that the majority were female (68.9%) and within the 18–30-year age group (66.7%). In terms of marital status, 62.2% were married, and a significant proportion (42.2%) had a monthly income of less than 5,000 riyals. A significant reduction in IBS severity scores was observed following the intervention. The mean IBS-SSS score decreased from 290 pre-intervention to 190 post-intervention. This reduction was accompanied by a shift in symptom severity categories.

Before the low-FODMAP dietary intervention, 82.2% of participants exhibited moderate IBS symptoms, while 17.8% experienced severe symptoms. Following the intervention, the proportion of participants with moderate symptoms increased slightly to 86%, whereas those with severe IBS decreased to 14% (Fig.1). Lastly, based on BMI classification, the majority of IBS patients (77.8%) were classified as having a normal weight.

Our study findings demonstrated the mean daily energy and nutrient intake among individuals diagnosed with IBS before and after participating in the low FODMAP intervention program, as shown in Table2. A significant difference (P < 0.01) was observed between pre- and post-intervention periods, highlighting the impact of the low-FODMAP intervention program on dietary consumption.

The energy levels experienced a significant decline with a large effect size (1.77), primarily attributed to the reduction in available energy sources. Notably, the most substantial impact was observed for the decrease in carbohydrates (effect size: 1.80) and fat (effect size: 1.42), while protein exhibited a moderate effect size (0.62). The levels of starch, sugars, and fibers were significantly reduced with a strong impact, with reductions of 1.28, 1.78, and 1.20, respectively. The FODMAPs exhibited a significant reduction, with the most pronounced impact size observed for fructo-oligosaccharides (1.61), followed by excess fructose (1.22), and lactose (0.86).

The findings of our study regarding the correlation between the severity of (IBS) symptoms and the intake of FODMAPs before and after participation in a low-FODMAP intervention program are displayed in Table3. The findings indicate that prior to the implementation of the low FODMAP intervention program, a significant difference (P < 0.05) was observed in the levels of lactose between patients experiencing severe symptoms of IBS and those with moderate symptoms. Specifically, patients with severe symptoms had a lower average lactose consumption (2.96 ± 1.15) compared to those with moderate symptoms (4.29 ± 1.54).

Following the completion of the low FODMAP intervention program, a significant difference (p < 0.05) was observed in the levels of sorbitol between patients exhibiting moderate symptoms of IBS (0.13 ± 0.08) and those with milder symptoms (0.24 ± 0.13), specifically in relation to their higher average intake of sorbitol.

The results of our study revealed a statistically significant association (p < 0.05) between fructo-oligosaccharides (FOS) intake and gender before the intervention program. Specifically, 67.7% of females had an above-average FOS intake compared to only 21.4% of males. However, after the intervention, no significant association was observed (p > 0.05). The post-intervention data showed that 46.2% of males had an above-average FOS intake, which was comparable to the 46.7% of females.

The association between lactose, fructose, sorbitol, and mannitol intake and gender was shown to be statistically significant before the intervention program (p < 0.05), Table4. Specifically, females had an above-average lactose intake compared to males. However, following the intervention program, no significant association was observed (p > 0.05) for lactose, fructose, and sorbitol. Finally, no significant association between gender and galacto-oligosaccharides both before and after the low FODMAP intervention program.

The association between age and the consumption of FODMAP items before and after the intervention program is shown in Table (5). There is a significant association between galacto-oligosaccharides and age after intervention program (p < 0.05), specifically favoring the age group of 18–30 years. However, no significant difference was observed between age groups in galacto-oligosaccharide levels at baseline (p > 0.05).

There is a significant association between lactose and fructose consumption and age before and after the intervention program(p < 0.05). Specifically, individuals in the age group of 31–45 years exhibit a higher intake of lactose above the average compared to those in the age group of 18–30 years. For mannitol, a significant relation was observed with the younger age group (18–30) after the intervention program (p < 0.05). Finally, no significant association between age groups and fructo-oligosaccharides or sorbitol both before and after the FODMAP intervention program.

The results of the study indicate that a significant proportion of individuals diagnosed with irritable bowel syndrome (IBS) were female, (68.9%). These findings align with previous research¹⁵ In Lebanon, 29.9% of identified IBS patients were female¹⁶, in Riyadh, 67.3% were female¹⁷, In Poland, 75.3% were female, and¹⁸ in Ireland, where 85% were female. Chatila et al. (2017) analysed the factors contributing to the greater incidence of IBS in females compared to males. These factors encompass heightened serotonin production in the brain, the correlation between IBS and pain relievers that mitigate pelvic-related symptoms such as those experienced during pregnancy and childbirth, and the influence of female sex hormones on gastrointestinal motility¹⁵.

Regarding the age groups, it was observed that the adult participants in our study had the highest prevalence of IBS, accounting for 66.7% of the total cases. These findings are consistent with the results reported by Almousa et al. (2018), who observed that a significant proportion of individuals diagnosed with IBS fell between the age range of 15 to 30 years (52.6%)¹⁶. Hustoft, et al. (2017) reported similar findings, with the majority of IBS patients having an average age of 35 years¹⁹. Furthermore, a study conducted by Chatila, et al. (2017) revealed that the prevalence of IBS among individuals aged 18–30 was 40.8%, whereas it was 27.4% among those aged 31–40¹⁵. According to Han, et al. (2006), there is a suggestion that the occurrence of IBS in individuals aged 20 and above could potentially be associated with factors such as academic stress, occupational demands, marital status, or financial circumstances¹⁹.

The findings of our study revealed a significant association between marital status and the heightened prevalence of IBS. This finding is consistent with research conducted by^{20] and [21}. Our findings indicate that persons with a lower monthly income exhibit a higher likelihood of experiencing IBS aligning with results from studies conducted by²², and²³.The latter found a positive correlation between a decline in monthly household income and an increase in functional gastrointestinal symptoms.

In our study, 77.8% of participants were within the normal weight range. Previous studies have demonstrated a positive correlation between obesity and the severity of IBS, with indications that symptoms tend to ameliorate after weight loss. Pickett-Blakely (2014) suggested the high incidence of IBS might be ascribed to factors such as increased consumption of carbohydrates and insufficient intake of dietary fibers²⁴.

Our results showed a significant reduction in IBS-SSS scores post-intervention, highlighting the effectiveness of the low-FODMAP diet in alleviating IBS symptoms. The prevalence of severe symptoms associated with IBS among participants who adhered to the low-FODMAP dietary intervention was consistent with the findings reported by²⁵. Moreover, specific types of carbohydrates, including fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs), have been recognized as significant factors in the manifestation of symptoms associated with IBS. Böhn, et al. (2015) illustrated that patients diagnosed with IBS possessed the ability to discern particular dietary items that exacerbated their symptoms²⁶. There were two distinct mechanisms for the IBS symptoms due to FODMAPs, Firstly, the malabsorption of (FODMAPs) within the small intestine results in elevated intra-intestinal pressure and subsequent fluid secretion into the large intestine, hence manifesting symptoms such as stomach pain. Furthermore, it has been shown that FODMAPs undergo fermentation by colonic bacteria, leading to the manifestation of symptoms such as abdominal pain, bloating, and heightened gas production. The implementation of a low-FODMAP diet is frequently advised as a means to ameliorate symptoms experienced by patients diagnosed with IBS. Several studies have demonstrated that strict adherence to a low-FODMAP diet results in symptom amelioration among individuals diagnosed with IBS²⁷.

Our results showed a notable reduction in the intake of carbohydrates, starches, sugars, and calcium. The results are consistent with the findings of^10,28,29,30. The decrease in FODMAP consumption could perhaps be attributed to the exclusion of specific food items such as fruits, vegetables, bread, pasta, honey, artificial sweeteners, and dairy products that contain lactose. No significant alterations in calorie, protein, and fat consumption were noted after 4 weeks. Our findings also showed a statistically significant reduction in riboflavin and vitamin C concentrations after participation in a low-FODMAP intervention. These findings are consistent with a study conducted by³¹.

Nevertheless, our research outcomes are incongruent with the study conducted by^{25] and [32} they reported no significant alterations in calorie consumption, carbohydrate intake, starch consumption, or sugar consumption subsequent to adhering to a low FODMAP diet. It is crucial to acknowledge that while adhering to a low FODMAP diet, the inclusion of high FODMAP items is substituted with low FODMAP alternatives, and seeking guidance from a proficient nutritionist aids in upholding nutritional equilibrium.

The results of our study showed that patients who followed the low-FODMAP intervention program had a decrease in the intensity of their symptoms. These findings align with^11,33,34. Moreover, our results indicate a significant correlation between gender and FODMAP consumption before and after participating in a low-FODMAP diet intervention program. Specifically, female participants exhibited elevated levels of FODMAP consumption prior to engaging in the intervention. This finding is consistent with^35,36,37. Jeffery, et al. (2009) indicated a positive correlation between symptoms of depression in females and the intake of high-calorie sweets³⁸. This suggests that sweetened foods may serve as a form of alleviation of the negative effects associated with depression. Furthermore, Dubé, et al. (2005) demonstrated that emotional stimuli can influence the consumption of comfort foods. In the case of females, negative emotions may lead to consuming foods rich in sugars and fats³⁹.

Authors and Affiliations

1. Department of Food and Nutrition, Faculty of Human Sciences and Design, King Abdulaziz University, Jeddah, Saudi Arabia

   Amani A. Alrasheedi&Esra A. Jahlan

2. Department of Family and Community Medicine, Faculty of Medicine, King Abdulaziz University, Rabigh, Saudi Arabia

   Marwan A. Bakarman

Contributions

A. A. and E. J. Data curation, A. A. and E. J. Formal analysis, (A) A., M. (B) and E. J Methodology, (A) A. Project administration. E. J. Resources, Visualization. M. (B) and E. J. Writing - original draft, A. A. review & editing.

Corresponding author

Correspondence to Amani A. Alrasheedi.

Competing interests

The authors declare no competing interests.

Study limitations

The main limitation of this study is the recruitment process for patients with IBS from hospitals posed difficulties, which may have affected the generalizability of our findings to a broader population of IBS patients. Additionally, the lengthy nature of the questionnaire may have discouraged some patients from participating. Another limitation is the use of a Food Frequency Questionnaire (FFQ), which relies on self-reported dietary intake. This method is prone to recall bias and inaccuracies in estimating actual consumption patterns. Moreover, FFQs may not fully capture daily variations in food intake, potentially affecting the precision of nutrient assessments. Despite these limitations, the FFQ remains a widely used and validated tool for assessing dietary patterns in nutritional research.

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