Does being overweight cause IBS?

I’m getting straight to the point with this one – There isn’t any evidence that being a heavier weight causes IBS.

But, what we eat, and the way food moves through the body can impact our body size, and can also affect digestive symptoms like bloating, gas, diarrhoea and constipation.

Is there a link between being overweight and IBS?

In this article I’ll show you how it’s not clear from the research that being in a larger body size causes IBS, or that having IBS causes weight gain.

However, we do know that IBS may be more common in people with a heavier weight.

And this is something I see with my clients in my online clinic.

Before we get started,  I want to acknowledge the limitations of using Body Mass Index (BMI) as a measure for someone’s health. The studies I’ve referenced all relate BMI to functional gut symptoms, so this is what I’ve used but just to be clear, having a larger BMI number doesn’t ultimately mean you’re unhealthy or are more likely to have IBS. 

What does the research say?

One small study showed 30% of people classed as obese had IBS, compared to a general population rate of around 10-15%. Obese is generally when you have a BMI of over 30.

Other research in 366 people showed 30% of people with IBS were classed as obese or overweight. However some research could not find link between IBS and obesity, so it’s still unclear.

There are however, definitely several associations between the two conditions and I’ll explain those below.

Would losing weight improve IBS symptoms?

There isn’t really evidence to show people in the largest bodies have the worst IBS. This means that losing weight won’t automatically help your gut issues.

In the same vein, resolving your IBS won’t cause you to lose weight unless you also engage in some dietary changes and exercise.

We can’t point to specific physiological mechanism for why you might have IBS and struggle to lose weight, but it is common to have both issues.

Many of my clients come to me for digestive issues, but also want to lose a bit of weight. 

Some examples of the links between weight and IBS symptoms include:

• Gastroesophageal reflux disease – Obesity is associated with a relaxed lower sphincter at the top of your stomach, which could allow stomach acid up into the oesophagus. This might be potentially due to increased abdominal pressure. Maintaining a lower BMI may reduce the likelihood of developing GERD and its potential complications.
• Slow transit time – there is a link between slow passage of food through the gut and increased energy intake. High fat, high protein meals can slow down your digestion. Some people with obesity be more likely to experience slow gut motility or constipation.
• Rapid stomach emptying – some people with a BMI over 30 may experience rapid stomach emptying into the small intestine than people in a smaller body size. This can cause diarrhoea, cramps and pain. It could be down to larger meals eaten, or a reaction to fats, sugars or certain fibres.

Is IBS more common if you’re overweight?

It is more likely you’ll have IBS if you have a larger body size, but definitely not a given. 

After adjusting the results to take into account age, sex, education level, alcohol and smoking, these studies [ii][iii][iv] found an association between a BMI of over 30 and increased risk of:

• heartburn – 1.6-1.9x more likely
• acid regurgitation – 2.1-2.22 x more likely
• increased bloating – 1.3x more likely
• increased stool frequency – 1.4x more likely
• loose and watery stools – 1.5-2.45x more likely
• and upper abdominal pain 1.3-2.21 x more likely

This shows that there is a potential link between your digestive problems, and a larger body size.

Improve IBS before weight loss

I know from working with lots of people that if you want to lose weight, you can only really do that when your digestion is properly functioning.

Once your digestion works better, you can then engage in the typical dieting advice such as eating more fruit and vegetables, increasing fibre and switching to wholegrain from white bread, pasta and rice.

Two keys to both weight loss and digestive health are firstly diet, and secondly the gut microbiome.

Diet for weight loss and IBS

Low fibre, high carbohydrate diets are linked to IBS symptoms and also associated with gaining weight.

A ‘typical Western diet’ is normally considered to be:

• low in fibre (which can affect stool regularity and gut motility)
• high in saturated fats (which may cause loose stools at high levels),
• and high in fermentable carbohydrates (such as fructose and lactose) causing loose stools, bloating and gas.

This diet pattern is may be driving your digestive issues if you’re eating this way over the long term.

It is also likely to lead to issues with metabolism and cardiovascular disease due to the low fibre, high fat aspects of the diet.

Changes in the gut microbiome

There are possible links between unhelpful changes in the gut microbes that could cause IBS symptoms, and also link to changes in weight.

We don’t yet know what makes a healthy gut microbiome, but we do know you can change gut when you alter your diet.

Can gut bacteria help you lose weight?

Unfortunately we’re not yet at the stage where we know which bacteria can help people lose weight, but we know there are microbes like Akkermansia muciniphila which are definitely seen more in people with a lean body shape. 

If you want to encourage more Akkermansia muciniphila into your gut then add more prebiotic fibres to your diet. You can read more about Prebiotics for IBS in my blog post. 

It is possible to see links between certain bacterial patterns and health conditions. 

• Some gut bacteria are more associated with a high fat diet.
• Methane producing bacteria, often higher in people with constipation, may be more likely to help you extract more energy from your food. 
• Some gut microbes are involved in insulin sensitivity, which could lead to metabolic changes over time. 
• Fermentation of supplementary prebiotic fibres has been shown to increase hormones (glucagon-like peptide 1 and peptide YY) which help us feel fuller. This study was done in healthy individuals which may produce a different result in people with obesity. 

Some people with small intestine bacterial overgrowth struggle to lose weight due to diet restrictions to manage their symptoms. In fact, SIBO was found in 41% of patients awaiting bariatric surgery.

Why is harder to lose weight when you have IBS?

You probably already know the basics of what makes up a healthy diet.

If you’re like most of my clients you’ve probably already tried all the normal diet advice. You can’t eat more vegetables, fruits and wholegrains, because they make you bloated, rush to the loo and have excess gas.

You might find ‘healthy food’ doesn’t suit your digestion. If this sounds familiar, you’re not alone.

One study from Romania showed people who have IBS tend to eat more canned food, processed meat and beef than people who don’t have digestive issues.

Another study from Holland showed people with IBS ate less fibre (21g vs 25g per day compared to controls). Fat accounted for more of their total energy intake than controls, and they ate more processed meat and more added sugars.

To lose weight you will need to make changes to your behaviours that have led you to put on weight in the first place. This can be very hard when the foods that might feel easier on your digestion are the particular foods that can lead to more weight gain.

If weight loss and IBS is something you’re struggling with at the moment you can book a free discovery call to chat about what you need help with. Just go to my contact page to book dierctly into my diary, or email me on info@goodnessme-nutrition.com to

[ii] Talley, N. J., Quan, C., Jones, M. P., & Horowitz, M. (2004). Association of upper and lower gastrointestinal tract symptoms with body mass index in an Australian cohort. Neurogastroenterology and motility : the official journal of the European Gastrointestinal Motility Society, 16(4), 413–419. https://doi.org/10.1111/j.1365-2982.2004.00530.x

[iii] Alkhowaiter, S., Alotaibi, R. M., Alwehaibi, K. K., Aljohany, A., Alruhaimi, B., Almasaad, M., Alshammari, S. A., & Alsahafi, M. A. (2021). The Effect of Body Mass Index on the Prevalence of Gastrointestinal Symptoms Among a Saudi Population. Cureus, 13(9), e17751. https://doi.org/10.7759/cureus.17751

[iv] Eslick, G. D., & Talley, N. J. (2016). Prevalence and relationship between gastrointestinal symptoms among individuals of different body mass index: A population-based study. Obesity research & clinical practice, 10(2), 143–150. https://doi.org/10.1016/j.orcp.2015.05.018