Bloating is one of the most common and stubborn symptoms experienced by as many as 96% of individuals with IBS. In fact, I'd venture to say it is the single most frequently discussed topic in nearly every initial assessment with clients. So if you're dealing with unpredictable or intractable bloating, you're certainly not alone, and there is plenty that can be done.

While it can be frustrating to deal with, understanding the underlying causes of IBS bloating can help us better manage and alleviate your symptom by customizing a care plan that addresses your most likely causes. Today we'll answer a few key questions to get you started:

• What is bloating?
• What is the difference between abdominal bloating and distension, and why does that matter? 
• What causes bloating in IBS?
• How do I know by IBS isn't something else?

Before we dive in, please note that it is crucially important to go in for a complete medical work-up if you're experiencing bloating that persist for over 72 hours or is accompanied with other changes in your physical health. Bloating is associated with numerous medical conditions of varying acuity, which is a fancy way of saying - bloating isn't always caused by IBS, and sometimes it's caused by something more serious. Find a doc you love, and share your symptoms with them. I'm going to be chatting a bit about how to do that here, as well! 

What is Bloating?

Abdominal bloating is a common and often uncomfortable symptom characterized by a sensation of fullness, tightness, or swelling in the abdomen. It can occur in both the upper and lower parts of the stomach and is often accompanied by visible distension, where the stomach area appears noticeably swollen or enlarged. Bloating can range from mildly uncomfortable to severely debilitating, interfering with daily activities and overall quality of life.

The sensation of bloating is frequently reported in individuals with digestive disorders, such as Irritable Bowel Syndrome (IBS) and Small Intestinal Bacterial Overgrowth (SIBO). It can result from various underlying causes, including excessive gas production, altered gut motility, impaired digestion, or an imbalance in the gut microbiome. Bloating is commonly triggered by certain foods, especially those rich in fermentable carbohydrates (FODMAPs), but it can also be exacerbated by factors like stress, hormonal fluctuations, and lifestyle habits. While bloating itself is not a disease, it can be a symptom of underlying gastrointestinal conditions that require medical attention.

Effective management often involves dietary modifications, such as adopting a low FODMAP diet, and incorporating lifestyle changes, including regular physical activity and stress management techniques. 

What is the Difference Between Bloating & Distension?

Abdominal bloating tends to refer to any subjective experience of discomfort in the abdomen. It can occur with or without any visible changes in how far out your belly is expanded. Distension, on the other hand, refers to an actual, measurable outward expansion of the belly (think: rocking the 8 months pregnant look). In other words, if you experience abdominal bloating, it is very important to indicate whether or not you experience bloating with or without distension. That distinction will help you identify your underlying risk factors and potential causes of bloating alongside your healthcare team. Plus, your doctor will be impressed that you can so eloquently articulate your symptoms! 

What Causes IBS Bloating?

Understanding the triggers and mechanisms behind IBS bloating is the first step to improve your digestive health and experience a greater quality of life. While the research continues to evolve, we do have a few ideas regarding underlying causes that lead to bloating in IBS.

Altered Gut Motility

Research indicates that one of the primary causes of bloating in IBS is altered gut motility. Gut motility refers to the contractions of the gastrointestinal muscles that mix and propel contents in the digestive tract. In IBS, these contractions can become irregular or overly intense, leading to a sensation of bloating, as well as cramping, constipation, or diarrhea. A recent systematic review highlighted that delayed intestinal transit, particularly in IBS-C (constipation predominant), contributes significantly to bloating. Studies suggest that motility disorders could stem from disruptions in the enteric nervous system or hormonal imbalances affecting the gut-brain axis, though the underlying etiology of IBS remains unknown [1].

Visceral Hypersensitivity

Visceral hypersensitivity is an increased sensitivity to pain within the internal organs. This is another significant cause of bloating in IBS, which makes the nerves in the gut more sensitive to stimuli, causing normal amounts of gas and fluid to feel excessive or painful. According to a 2023 meta-analysis, patients with IBS have heightened visceral perception, making them more likely to experience bloating and discomfort [2]. This hypersensitivity may result from genetic predispositions or previous infections, food poisoning, and inflammation that have sensitized the gut lining.

Microbiome Dysbiosis

An imbalance in the gut microbiota has been implicated in the pathogenesis of IBS and its associated symptoms, including bloating. A 2022 systematic review found a strong correlation between altered gut flora and increased bloating in IBS patients [3]. This imbalance was also associated with increased gas production and changes in the bacterial fermentation processes. Dietary changes, such as a minimally restrictive low FODMAP approach, have been shown to reduce bloating in individuals with IBS by minimizing symptoms associated with osmotic pressure and bacterial fermentation in the gut. 

It is also worth nothing that there is a significant overlap between IBS and Small Intestinal Bacterial Overgrowth (SIBO) or Intestinal Methanogen Overgrowth (IMO). Research indicates that up to 78% of IBS patients may also have SIBO, but the question still remains regarding which condition "causes" the other. A 2024 systematic review noted that SIBO is more prevalent in patients with IBS-D (diarrhea-predominant IBS) and IBS-M (mixed type) due to altered gut motility and increased small bowel bacterial load [6]. While IBS and SIBO/IMO share common symptoms such as bloating, abdominal pain, and altered bowel habits, there are distinct differences to consider. SIBO/IMO typically presents with symptoms that worsen after meals and are associated with significant mid-abdominal bloating and flatulence with nearly all fermentable carbohydrates. In contrast, IBS symptoms may fluctuate more with stress and emotional triggers and often include abdominal pain, which is commonly relieved by defecation. Further, IBS symptoms tend to be worse in the mornings, while SIBO/IMO symptoms tend to progress throughout the day. If you suspect you have SIBO/IMO, consult with your gastroenterologist before making any diet adjustments.

Dietary Triggers and Food Intolerances

Certain foods are known to exacerbate bloating in IBS patients, particularly those containing fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs). Foods high in FODMAPs can lead to increased fermentation or water draw in the gut, resulting in gas production and bloating. A recent clinical trial conducted in 2023 demonstrated that a low-FODMAP diet significantly reduced bloating and abdominal discomfort in IBS patients [4]. The study supports personalized dietary interventions as a cornerstone of IBS management, focusing on identifying and eliminating individual food triggers with a minimally-restrictive approach.

Psychological Factors and Stress

Psychological factors, including stress and anxiety, are closely linked with IBS symptoms. The gut-brain axis plays a crucial role in this connection, where psychological stress can alter gut motility and sensitivity, leading to symptoms like bloating. A systematic review published in 2024 highlighted that stress management techniques, such as cognitive-behavioral therapy (CBT) and gut-directed hypnotherapy, effectively reduce bloating and improve overall quality of life in IBS patients [5]. The findings underscore the importance of a holistic treatment approach that includes both physical and psychological interventions.

How Do I Know My IBS Isn't Something Else?

There's a significant overlap between IBS symptoms and symptoms caused by other digestive conditions. To discern between the two, it is imperative that you have gone through the proper diagnostic process with a gastroenterologist that you know, like, and trust. Even if IBS is suspected, there are additional tests and procedures that must be done to rule out other conditions, like Celiac disease, Inflammatory Bowel Diseases, and Small Intestinal Bacterial Overgrowth, among others. A colonoscopy is often indicated, though IBS can be diagnosed without scopes.

Bloating in IBS is multifactorial, involving altered motility, visceral hypersensitivity, microbiome imbalances, dietary triggers, and psychological factors. Addressing bloating effectively requires a comprehensive approach that considers all these factors holistically. To learn more about managing IBS through evidence-based dietary changes and a holistic lifestyle approach, download our free IBS Microbiome Reset Meal Plan or check out our Plant-Based IBS and SIBO Breakfast Book.

References & Further Reading

1. Rao SS, Camilleri M, Hasler WL, et al. Gut motility disorders and IBS: Pathophysiology and clinical implications. Clin Gastroenterol Hepatol. 2024;22(1):34-40.
2. Fukudo S, Kanazawa M, Sagami Y, et al. Visceral hypersensitivity in irritable bowel syndrome: A review. Neurogastroenterol Motil. 2023;35(2).
3. Ghoshal UC, Srivastava D, Verma A. Microbiome dysbiosis in irritable bowel syndrome: Evidence and clinical relevance. World J Gastroenterol. 2022;28(7):742-751.
4. Halmos EP, Power VA, Shepherd SJ, et al. A low FODMAP diet in the management of irritable bowel syndrome: A systematic review and meta-analysis. J Gastroenterol Hepatol. 2023;38(5):569-577.
5. Ford AC, Lacy BE, Talley NJ. Stress management for irritable bowel syndrome: The role of psychological therapies. Gut. 2024;73(9):1391-1398.
6. Rezaie A, Bures J, Lembo A, et al. Overlap of irritable bowel syndrome and small intestinal bacterial overgrowth: A systematic review and meta-analysis. Gastroenterology. 2024;167(3):519-528.