Abdominal fullness is an experience almost everyone has had, especially after a big meal. The food that feels like it’s about to burst your belly might even make you forget the joy of the feast you just enjoyed, and deeply experience the discomfort of overindulgence. Similarly, you’ve probably heard the term “bloating.” Bloating is different from the fullness you feel after a meal; it’s not necessarily related to eating. You might feel like your stomach is constantly filled with air, or that your abdomen has expanded.

The Chinese term “脹氣” (zhangqi) actually encompasses two meanings in Western medicine: “Abdominal bloating (脹氣)” and “Abdominal distension (腹部膨大).” The former refers to a subjective feeling of recurrent fullness, pressure, or trapped air in the abdomen; the latter refers to an objective increase in abdominal girth (for a more detailed diagnostic description, refer to the 2016 ROME IV Criteria [1] definition of Functional Abdominal Bloating/Distension).

Abdominal bloating is medically classified as a type of Functional Gastrointestinal Disorder (FGID). Although these conditions are prevalent in the population, no obvious organ damage or physiological abnormalities have been found [2]. Consequently, their causes are not well understood.

Epidemiological data from 2015 shows that approximately 30% of adults experience symptoms of abdominal bloating, and it almost always co-occurs with another functional gastrointestinal disorder: Irritable Bowel Syndrome (IBS). Furthermore, only 50% of people who feel bloated actually experience objective abdominal distension. This means that bloating and abdominal distension do not necessarily occur simultaneously. However, for the convenience of explanation in this article, “bloating” will refer to the symptomatic feeling of bloating, and if it refers to objective abdominal distension, I will specifically label it as (distension).

To date, there is no definitive conclusion regarding the causes of abdominal bloating. However, many hypotheses have been proposed. Let’s analyze the possible causes of abdominal bloating one by one!

Too Much Air in the Abdomen?

When people talk about abdominal bloating, it’s naturally assumed to be related to an excessive accumulation of air in the abdomen. When we drink carbonated beverages, eat too quickly, or even chew gum, we often swallow too much air (Aerophagia). However, generally speaking, swallowing too much air is not the primary cause of abdominal bloating, for two reasons:

  1. When too much air is swallowed, the body’s balancing mechanisms cause us to burp more, so the rate of gas accumulation in the gastrointestinal tract cannot exceed the rate of gas expulsion.
  2. Gases entering the small intestine, such as CO2 and O2, can quickly diffuse across the intestinal wall and enter the body. Even N2, which is harder to absorb, can be expelled through flatulence.

In 2009, Accarino et al. [3] used abdominal CT scans to compare the intra-abdominal volume during bloating episodes with non-bloating periods in affected individuals, finding almost no difference between the two. This refuted the idea that the amount of gas in the abdomen is the key factor causing bloating.

A 2001 study by Serra et al. [4] also suggested that, while accumulated gas in the abdomen can indeed cause objective abdominal distension, the discomfort symptoms of bloating are actually less related to the volume of intestinal gas and more likely related to intestinal motility.

Do Intestinal Bacteria Produce Different Gases?

Besides being swallowed through the mouth, much of the gas in the abdomen is actually produced by intestinal bacteria themselves. Therefore, some researchers have investigated whether the composition of gut microbiota differs between people with bloating and healthy individuals. A 2009 study by Collins et al. [5] indicated that altering the proportion of normal gut microbiota might affect the intestinal immune system, leading to abnormal inflammation. These changes could potentially cause abnormalities in intestinal sensory or motor function, resulting in bloating.

Furthermore, after the proportion of gut microbiota is altered, the composition and volume of gas within the intestines may also be affected. An interesting study [6] showed that individuals who produce less methane gas are more prone to experiencing bloating after consuming sorbitol (the substance often added to chewing gum) or fiber.

Currently, these changes in gut microbiota are frequently observed in patients with Irritable Bowel Syndrome (IBS), a major functional gastrointestinal disorder. Patients with IBS often experience bloating symptoms. Therefore, changes in gut microbiota are considered one of the possible mechanisms causing bloating.

Is It Just Psychological?

Many studies have indicated that patients with IBS or bloating have a lower threshold for abdominal sensations. In other words, a mild abdominal stimulus that would be unnoticed by most people might be distinctly felt, or even cause pain, for these patients.

Past research has also suggested that patients with IBS tend to over-focus on their abdominal symptoms, making them more prone to experiencing discomfort. [7]

A popular research area in recent years is the gut-brain axis. Simply put, it explores the unique relationship between the gut and the brain. Therefore, some believe that abnormal abdominal sensations, such as bloating, may also be related to the regulation of the gut-brain axis. These regulatory systems include neuroendocrine systems, the autonomic nervous system, and even central nervous system regulation of emotion and cognition. Research has already indicated that anxiety and depression are linked to intestinal inflammation [8], and thus abnormal cognitive function is currently also considered to be closely related to abdominal bloating.

It’s worth noting that women during menstruation are also more prone to abdominal bloating discomfort. Although the exact mechanism is still unclear, an exaggerated perception of stimuli could be one of the underlying reasons.

Can Being Overweight Also Cause Bloating?

Many studies have indicated that a sudden increase in body weight can exacerbate bloating discomfort, and conversely, weight loss is associated with symptom relief. The underlying reason may be related to the amount of abdominal fat.

But what is the relationship between obesity and bloating?

Firstly, abdominal fat may compress the fluid- or gas-filled intestines, stimulating sensory receptors on the peritoneum; secondly, fat on the mesentery or omentum can promote the release of inflammatory hormones, causing inflammation in the abdomen, which in turn leads to abnormal sensations; finally, another reason is actually related to psychological factors [7]: when the abdomen enlarges due to fat accumulation, patients may become overly conscious of stimuli in this area, thereby intensifying the sensation of bloating.

Do Muscle Contraction Patterns Change During Bloating?

A 2006 study by Tremolaterra et al. [9] showed that when our abdomen is filled with air, a normal person’s diaphragm should relax and elevate, creating space within the abdominal cavity for this gas, while the internal oblique muscles contract to flatten the abdomen, preventing it from bulging out too much. Conversely, in patients with bloating, there is a completely opposite muscle reflex: their diaphragm contracts and descends, while the internal oblique muscles relax. The result is that gas is pushed downwards, and the abdomen, lacking the pressure from the internal oblique muscles, easily expands outwards, explaining the visually observed phenomenon of abdominal distension.

How to Prevent Bloating

According to data from Johns Hopkins University in the United States, general prevention of bloating can start with diet. Reduce consumption of foods containing oligosaccharides, disaccharides, monosaccharides, polyols, or sugar alcohols. The reason is that these substances are less easily metabolized in the small intestine; they travel to the large intestine where they are broken down by bacteria, producing gas, which may be related to bloating. These foods include:

Oligosaccharides: wheat, onions, garlic, legumes, etc. Disaccharides: lactose in milk, yogurt, ice cream, etc. Monosaccharides: fructose in honey, apples, pears, etc. Polyols or Sugar Alcohols: plums, nectarines, broccoli, chewing gum, candies, etc.

In terms of treatment, if a patient has constipation, assisting with bowel movements may alleviate bloating, or even antibiotics can be used to alter the gut microbiota. However, these interventions must be implemented under a doctor’s evaluation!

Conclusion

Although the Chinese term for bloating (脹氣) contains the character for “gas” (氣), and the mechanisms of bloating are indeed related to intestinal gas, many studies show that bloating is not truly caused by excessive gas, but rather by other underlying issues in our body. These include abnormal abdominal sensations, dysfunctional gas expulsion mechanisms, obesity, changes in gut microbiota, and more. Additionally, dietary habits may also be a major key factor contributing to bloating. By changing lifestyle habits, it is still possible to say goodbye to bothersome bloating!

References

  1. Malagelada, J. R., Accarino, A., & Azpiroz, F. (2017). Bloating and abdominal distension: old misconceptions and current knowledge. American Journal of Gastroenterology, 112(8), 1221-1231.
  2. Mari, A., Backer, F. A., Mahamid, M., Amara, H., Carter, D., Boltin, D., & Dickman, R. (2019). Bloating and Abdominal Distension: Clinical Approach and Management. Advances in therapy, 36(5), 1075-1084.
  3. Seo, A. Y., Kim, N., & Oh, D. H. (2013). Abdominal bloating: pathophysiology and treatment. Journal of neurogastroenterology and motility, 19(4), 433.
  4. John Hopkins： https://www.hopkinsmedicine.org/health/wellness-and-prevention/bloating-causes-and-prevention-tips
  5. UptoDate Patient education

Research Data Mentioned in the Article

[1]：Lacy, B. E., Mearin, F., Chang, L., Chey, W. D., Lembo, A. J., Simren, M., & Spiller, R. (2016). Bowel disorders. Gastroenterology, 150(6), 1393-1407. [2]：Mukhtar, K., Nawaz, H., & Abid, S. (2019). Functional gastrointestinal disorders and gut-brain axis: What does the future hold?. World journal of gastroenterology, 25(5), 552. [3]：Accarino, A., Perez, F., Azpiroz, F., Quiroga, S., & Malagelada, J. R. (2009). Abdominal distention results from caudo-ventral redistribution of contents. Gastroenterology, 136(5), 1544-1551. [4]：Serra, J., Azpiroz, F., & Malagelada, J. R. (2001). Mechanisms of intestinal gas retention in humans: impaired propulsion versus obstructed evacuation. American Journal of Physiology-Gastrointestinal and Liver Physiology, 281(1), G138-G143. [5]：Collins, S. M., Denou, E., Verdu, E. F., & Bercik, P. (2009). The putative role of the intestinal microbiota in the irritable bowel syndrome. Digestive and Liver disease, 41(12), 850-853. [6]：Vernia, P., Di Camillo, M., Marinaro, V., & Caprilli, R. (2003). Effect of predominant methanogenic flora on the outcome of lactose breath test in irritable bowel syndrome patients. European journal of clinical nutrition, 57(9), 1116-1119. [7]：Accarino, A. M., Azpiroz, F. E. R. N. A. N. D. O., & Malagelada, J. R. (1997). Attention and distraction: effects on gut perception. Gastroenterology, 113(2), 415-422. [8]：Ghia, J. E., Blennerhassett, P., & Collins, S. M. (2008). Impaired parasympathetic function increases susceptibility to inflammatory bowel disease in a mouse model of depression. The Journal of clinical investigation, 118(6), 2209-2218. [9]：Tremolaterra, F., Villoria, A., Azpiroz, F., Serra, J., Aguadé, S., & Malagelada, J. R. (2006). Impaired viscerosomatic reflexes and abdominal-wall dystony associated with bloating. Gastroenterology, 130(4), 1062-1068.

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