Gut Microbiota and Nutrition in Irritable Bowel Syndrome: The New Science Behind an Old Pain

 The information in this article is entirely based on the comprehensive scientific review "Intestinal Microbiota And Diet in IBS: Causes, Consequences, or Epiphenomena?" published in the prestigious journal The American Journal of Gastroenterology (2015, Volume 110, pp. 278–287), DOI: 10.1038/ajg.2014.427. The authors include renowned scientists and clinicians from various countries and fields, such as Mirjana Rajilić-Stojanović (PhD, University of Belgrade), Daisy M. Jonkers (PhD, Maastricht University), Anne Salonen (PhD, University of Helsinki), Kurt Hanevik (MD, PhD, University of Bergen), Jeroen Raes (PhD, KU Leuven), and dozens of other leading experts in microbiology, gastroenterology, immunology, and psychology. The publication analyzes the role of gut microbiota and dietary factors in the development and manifestations of irritable bowel syndrome (IBS), summarizing the latest evidence from clinical practice and laboratory research. All the questions and answers below are strictly aligned with the findings of this international team.

“Diet and gut microbiota are closely intertwined in the onset and management of symptoms in irritable bowel syndrome. Understanding this interaction is key to a better life for patients.”

What the Experts Say

IBS is one of the most common gastrointestinal disorders, affecting up to 10–15% of the population in industrialized countries. Symptoms vary greatly between individuals and often include pain, bloating, diarrhea, or constipation. In recent years, science has uncovered the critical role of gut microbiota and nutrition—not only as symptom triggers but also as potential therapeutic tools. Here are five of the most current expert opinions and scientific summaries from top researchers in the field, offering practical insights for patients and their families.

1. Can diet trigger or relieve IBS symptoms?

“The environment we live in, and especially our diet, plays a significant role in the development and manifestation of IBS. Diet provides substrates for microbial fermentation, and the composition of the gut microbiota in IBS patients often differs from that of healthy individuals. The link between food, microbiota composition, and fermentation byproducts may be key in symptom generation.”

Explanation: This expert opinion emphasizes that individual responses to food in IBS are due to the unique interaction between diet and the microbiome. Changing one’s diet can rapidly alter the composition and function of gut microbiota, which directly impacts symptoms.

2. Which foods most commonly trigger IBS symptoms?

“Between 64–89% of IBS patients report that their symptoms are triggered by meals or specific foods... The most frequently reported are wheat/grains, vegetables, dairy products, fatty foods, spicy foods, coffee, and alcohol—these foods are particularly associated with abdominal pain and gas.”

Explanation: While many patients self-limit certain foods, doing so without professional guidance poses a risk of nutritional deficiencies. Elimination diets should be conducted under the supervision of a dietitian.

3. What is the role of the FODMAP diet in IBS?

“The concept of intolerance to poorly absorbed and rapidly fermented carbohydrates led to the development of the FODMAP diet (fermentable oligo-, di-, mono-saccharides and polyols)... Randomized controlled trials show significant improvement in overall symptoms, abdominal pain, and bloating in IBS patients following a low-FODMAP diet.”

Explanation: The low-FODMAP diet has become one of the most effective non-pharmacological interventions for symptom relief in IBS, particularly in patients with bloating and diarrhea. However, it should be followed under professional guidance to avoid nutrient deficiencies and unwanted changes in microbiota.

4. Is there a difference in microbiota between people with IBS and healthy individuals?

“Numerous studies show differences in microbial profiles between IBS patients and healthy controls... Recent data indicate increased relative abundance of Firmicutes (mainly Clostridium cluster XIVa and Ruminococcaceae) and a decrease in Bacteroidetes... Bifidobacteria levels are also lower in IBS.”

Explanation: These shifts are often associated with symptoms such as increased gas production. Supplementing with probiotics—especially Bifidobacterium—may be beneficial, though there is still no consensus on which strains are most effective.

5. What does the future hold—and what are scientists recommending?

“Better-designed studies are needed to assess the effect of food on symptom generation and the underlying mechanisms... The potential benefits of FODMAP restriction seem promising but require further research and dietary guidance due to the risk of inadequate nutrient intake. More data is also needed on long-term effects and how the microbiota is altered by such interventions.”

Explanation: In the future, therapies will likely be personalized—tailored to both the symptom profile and the microbiota composition of each patient. Introducing customized dietary approaches based on microbiome analysis is one of the most promising directions.

Q&A Section

1. Does my long-term diet affect my gut microbiota—and how does that influence IBS? 

Answer: Yes, long-term eating habits have a significant effect on the composition of your gut microbiota. For example, diets high in protein and animal fats are associated with the so-called Bacteroides enterotype, while carbohydrate-rich diets promote the Prevotella enterotype. These microbial differences can influence how your body responds to specific foods and what IBS symptoms you may experience.

2. Why do some people with IBS experience more gas and bloating than others? 

Answer: This often relates to the microbiota and how it breaks down carbohydrates. IBS patients tend to have more gas-producing bacteria (like Dorea species) and fewer methane-producing microbes (which typically help remove hydrogen gas). This imbalance can lead to excess gas buildup and a stronger sensation of bloating and abdominal pain.

3. Is there a difference in microbiota between those with diarrhea-predominant IBS (IBS-D) and those with constipation-predominant IBS (IBS-C)? 

Answer: Yes, the article notes that methane-producing bacteria are more common in people with IBS-C and less common in those with IBS-D. Increased methane slows down intestinal transit and can contribute to constipation, while the absence of these bacteria may result in faster transit, leading to diarrhea and bloating.

4. What are the potential risks of following a low-FODMAP diet long term? 

Answer: Although the low-FODMAP diet can relieve symptoms for many IBS patients, it also reduces beneficial Bifidobacteria in the gut, along with other helpful bacteria that produce butyrate. This may have negative effects on long-term gut health and requires careful monitoring by a nutrition professional.

5. Can the microbiota from an IBS patient cause symptoms in healthy people or animals? 

Answer: Yes, scientific experiments have shown that transplanting microbiota from IBS patients into lab rats or mice can induce IBS-like symptoms, such as increased gut sensitivity and faster transit. This suggests that the microbiome plays an active role in the development of the condition, not just as a consequence.

Conclusion 

The latest scientific findings presented in the article by Rajilić-Stojanović and colleagues highlight that IBS is an extremely complex and individualized condition, shaped by subtle interactions between diet, gut microbiota, and the unique features of each person’s body. It is crucial for patients to understand that there is no one-size-fits-all approach to IBS; the best results come from careful, evidence-based tracking and personalized nutritional and therapeutic strategies. Advances in microbiome research are expected to lead to even more precise and effective recommendations for people living with this common and socially significant disorder.

Sources: Rajilić-Stojanović, M., Jonkers, D.M., Salonen, A., et al. "Intestinal Microbiota And Diet in IBS: Causes, Consequences, or Epiphenomena?" The American Journal of Gastroenterology, 2015; 110:278–287. doi: 10.1038/ajg.2014.427.