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Obesity and Irritable Bowel Syndrome (IBS)

Obesity and IBS are separate and distinct illnesses that share some suspicious commonalities.

Obesity and Irritable Bowel Syndrome (IBS)

Obesity and Irritable Bowel Syndrome (IBS) are two prevalent health conditions that have a complex and multifaceted relationship. While IBS is a functional gastrointestinal disorder characterized by abdominal pain, bloating, and altered bowel habits, obesity is a chronic disease defined by an excessive accumulation of body fat. This article delves deeper into the known relationships between obesity and IBS in humans, focusing on factors such as inflammation, gut microbiota, diet and lifestyle, psychological factors, and comorbidities. Additionally, this article will provide an expanded discussion on the gut microbiome, its association with both obesity and IBS, and how it may impact their relationship.


A higher prevalence of IBS has been observed in individuals with obesity compared to those with normal weight (Talley et al., 1995). However, more research is needed to establish a definitive causal relationship between obesity and IBS. According to a systematic review and meta-analysis by Aasbrenn et al. (2016), there is a modest but significant association between obesity and the risk of IBS. Nevertheless, the authors suggest further studies to confirm the relationship and explore potential underlying mechanisms.


Aasbrenn, M., Lydersen, S., & Farup, P. G. (2016). A conservative weight loss intervention relieves bowel symptoms in morbidly obese subjects with irritable bowel syndrome: A prospective cohort study. Journal of Obesity, 2016, 1–7. Talley, N. J., Quan, C., Jones, M. P., & Horowitz, M. (1995). Association of upper and lower gastrointestinal tract symptoms with body mass index in an Australian cohort. Neurogastroenterology & Motility, 7(2), 65–72.


Obesity is often associated with low-grade chronic inflammation, which can impact gut health. This inflammation may lead to changes in the gut microbiota, increased intestinal permeability, and altered gut-brain signaling, all of which could potentially contribute to IBS symptoms (Russo et al., 2018). Inflammation in the adipose tissue has been observed in individuals with obesity, and this adipose tissue inflammation may play a role in the development of IBS symptoms by affecting the gut-brain axis (Piche, 2014).


Russo, F., Chimienti, G., & Riezzo, G. (2018). Adipose tissue-derived biomarkers of intestinal barrier functions for the characterization of diarrhoea-predominant IBS. Disease Markers, 2018, 1–12. Piche, T. (2014). Tight junctions and IBS--the link between epithelial permeability, low-grade inflammation, and symptom generation? Neurogastroenterology & Motility, 26(3), 296–302.

Gut microbiota

Gut microbiota refers to the complex community of microorganisms that inhabit the human gastrointestinal tract. Dysbiosis, or an imbalance in the gut microbial community, has been linked to the development or exacerbation of IBS symptoms (Jeffery et al., 2012). Obesity has also been shown to cause alterations in the gut microbiota (Turnbaugh et al., 2006), which might play a role in the development of IBS.

Alterations in the gut microbiota can lead to changes in the production of short-chain fatty acids (SCFAs), which play a vital role in maintaining gut health and immune homeostasis. SCFAs can also influence the gut-brain axis, which is involved in modulating IBS symptoms (Dalile et al., 2019). Studies have shown that individuals with IBS have a different gut microbiota composition compared to healthy individuals, with a lower abundance of beneficial bacteria such as Bifidobacteria and Lactobacilli (Pittayanon et al., 2019). Similarly, individuals with obesity also exhibit an altered gut microbiota profile, with a higher ratio of Firmicutes to Bacteroidetes, which may contribute to obesity-related complications (Ley et al., 2006).

The interplay between obesity and IBS, mediated by the gut microbiota, is an area of ongoing research. Although the exact mechanisms remain unclear, it has been proposed that interventions targeting the gut microbiota, such as probiotics, prebiotics, and fecal microbiota transplantation, may be beneficial in managing both conditions (Mazurak et al., 2018).


Jeffery, I. B., O'Toole, P. W., Öhman, L., Claesson, M. J., Deane, J., Quigley, E. M. M., & Simrén, M. (2012). An irritable bowel syndrome subtype defined by species-specific alterations in faecal microbiota. Gut, 61(7), 997–1006.

Turnbaugh, P. J., Ley, R. E., Mahowald, M. A., Magrini, V., Mardis, E. R., & Gordon, J. I. (2006). An obesity-associated gut microbiome with increased capacity for energy harvest. Nature, 444(7122), 1027–1031.

Dalile, B., Van Oudenhove, L., Vervliet, B., & Verbeke, K. (2019). The role of short-chain fatty acids in microbiota–gut–brain communication. Nature Reviews Gastroenterology & Hepatology, 16(8), 461–478.

Pittayanon, R., Lau, J. T., Yuan, Y., Leontiadis, G. I., Tse, F., Surette, M., & Moayyedi, P. (2019). Gut microbiota in patients with irritable bowel syndrome—a systematic review. Gastroenterology, 157(1), 97–108.

Ley, R. E., Turnbaugh, P. J., Klein, S., & Gordon, J. I. (2006). Microbial ecology: Human gut microbes associated with obesity. Nature, 444(7122), 1022–1023.

Mazurak, N., Broelz, E., Storr, M., & Enck, P. (2018). Probiotic therapy of the irritable bowel syndrome: Why is the evidence still poor and what can be done about it? Journal of Neurogastroenterology and Motility, 24(4), 471–485.


Diet and lifestyle

Poor dietary habits and sedentary lifestyles, which are common in individuals with obesity, can contribute to gastrointestinal symptoms and may exacerbate IBS. Diets high in fat and low in fiber have been associated with a higher risk of developing IBS (Gibson & Shepherd, 2010). Furthermore, a study by Böhn et al. (2015) found that a low-FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet significantly improved IBS symptoms in a randomized controlled trial.

Physical inactivity may also contribute to the development of gastrointestinal symptoms. A study by Johannesson et al. (2011) demonstrated that increased physical activity improved IBS symptoms in patients. Moreover, engaging in regular physical activity has been shown to positively impact gut microbiota composition and diversity, which may indirectly benefit individuals with IBS (Monda et al., 2017).



Gibson, P. R., & Shepherd, S. J. (2010). Evidence-based dietary management of functional gastrointestinal symptoms: The FODMAP approach. Journal of Gastroenterology and Hepatology, 25(2), 252–258.

Böhn, L., Störsrud, S., Liljebo, T., Collin, L., Lindfors, P., Törnblom, H., & Simrén, M. (2015). Diet low in FODMAPs reduces symptoms of irritable bowel syndrome as well as traditional dietary advice: A randomized controlled trial. Gastroenterology, 149(6), 1399–1407.e2.

Johannesson, E., Simrén, M., Strid, H., Bajor, A., & Sadik, R. (2011). Physical activity improves symptoms in irritable bowel syndrome: A randomized controlled trial. The American Journal of Gastroenterology, 106(5), 915–922.

Monda, V., Villano, I., Messina, A., Valenzano, A., Esposito, T., Moscatelli, F., … Messina, G. (2017). Exercise modifies the gut microbiota with positive health effects. Oxidative Medicine and Cellular Longevity, 2017, 1–8.


Psychological factors

There is a known relationship between psychological factors and IBS, with stress and anxiety often exacerbating IBS symptoms. Individuals with obesity may experience increased levels of stress, anxiety, or depression, which could contribute to the development or worsening of IBS symptoms (Fond et al., 2014). Furthermore, the bidirectional communication between the gut and the brain, known as the gut-brain axis, plays a crucial role in both IBS and obesity. Alterations in this axis, such as those caused by stress, may lead to gastrointestinal dysfunction and changes in eating behaviors, potentially contributing to both IBS and obesity (Mayer et al., 2014).


Fond, G., Loundou, A., Hamdani, N., Boukouaci, W., Dargel, A., Oliveira, J., … Boyer, L. (2014). Anxiety and depression comorbidities in irritable bowel syndrome (IBS): A systematic review and meta-analysis. European Archives of Psychiatry and Clinical Neuroscience, 264(8), 651–660.

Mayer, E. A., Labus, J. S., Tillisch, K., Cole, S. W., & Baldi, P. (2014). Towards a systems view of IBS. Nature Reviews Gastroenterology & Hepatology, 12(10), 592–605.



Both IBS and obesity are associated with several comorbidities, such as cardiovascular diseases, type 2 diabetes, and certain gastrointestinal disorders. The presence of these comorbid conditions might influence the relationship between obesity and IBS, making it more difficult to establish a direct causal link. For instance, obesity-related comorbidities like type 2 diabetes may independently alter gut motility and sensation, thereby confounding the relationship between obesity and IBS (Lee et al., 2017).


Lee, C. G., Park, D. I., Park, J. H., Kim, H. J., Cho, Y. K., Sohn, C. I., … Kim, B. I. (2017). The risk of irritable bowel syndrome in patients with type 2 diabetes mellitus: A national population-based study. Medicine, 96(45), e8425.


In summary, the relationship between obesity and irritable bowel syndrome in humans is complex and multifactorial. While a higher prevalence of IBS is observed in individuals with obesity, the exact causal relationship and underlying mechanisms are still not fully understood. Factors such as inflammation, gut microbiota, diet and lifestyle, psychological factors, and comorbidities seem to be involved in this interplay. Moreover, the gut microbiome plays a critical role in both obesity and IBS, making it a promising target for interventions aimed at managing both conditions. Further research is needed to better understand the interplay between obesity and IBS and develop effective strategies for managing and preventing these conditions.

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