Most of us have experienced temporary bloating in some shape or form, whether after a heavy meal, during indulgent periods (such as festive holidays) or, unfortunately for some, more persistently due to digestive health problems.
What is bloating?
Bloating describes the sensation associated with gas or air in our gut i.e. feeling windy, when your abdomen feels swollen and the abdomen is commonly (but not always) distended (Seo et al, 2013). It makes us feel full, uncomfortable and is sometimes even accompanied by pain. It is also associated with other symptoms such as flatulence and nausea.
Why do we bloat?
In a healthy individual, even before eating (i.e. when we are fasted), our gastrointestinal tract (mainly from the stomach to the large intestine) is made up of gases. It is estimated that this is about 100-200ml in the fasted state, mainly made up of carbon dioxide, oxygen, nitrogen and hydrogen (Lacy et al, 2011). After we eat, the volume of gas can increase by 65% (Perez et al, 2007); some gas is swallowed during eating and gases are also produced during digestion and, to a smaller extent, by our gut bacteria in the large intestine (discussed below).
As you can imagine, our stomachs and the rest of our guts fill up with food, water and their digestion products on a daily basis. What we eat can also affect bloating. For example, eating rich, fatty meals delays the movement of these foods from the stomach into the small intestine (known as gastric emptying), meaning that digestion is slowed. In some people, eating foods high in dietary fibre, such as pulses, may lead to bloating due to an increase in gas production in the gut, but in others fibre can actually reduce bloating by improving digestion and reducing gut transit time.
How we eat is also important. When we swallow, air enters our stomach and can lead to abdominal distention. This is enhanced when we eat too quickly, drink a lot of liquids whilst eating, when our meals are too hot or when we consume fizzy drinks, and swallowing too much air is called aerophagia.
Can cutting out foods banish that bloat?
In individuals with food intolerances, eating such foods can lead to bloating. For example, those who are lactose intolerant do not have the enzyme lactase to digest lactose in cows’ milk, so this is broken down by gut bacteria in the large bowel, and consequently produces gases and bloating. Another example is in patients with inflammatory bowel syndrome (IBS), where eating foods containing Fermentable, Oligosaccharides, Disaccharides, Monosaccharides and Polyols (FODMAPs) increases gas production due to digesting these foods poorly (discussed later).
Stress is another lifestyle factor that can promote bloating. This can be a bit of a vicious cycle, whereby stress and anxiety can exacerbate bloating, which in turn causes more distress. One of the ways that stress can lead to bloating is by disturbing our ability to digest foods well. It does this via the gut-brain axis, which sends communications between our brain and our gastrointestinal tract. Stress can affect the communication mechanisms with the brain: neural, immune and hormonal, for example by changing levels of neurotransmitters, as well as cause constipation by affecting gut motility, which in turn can promote bloating (discussed below).
Hormones and bloating
In the UK, women (62%) report feeling bloated more commonly than men (41%) (Guts UK, 2016). This is likely due to differences and fluctuations in the levels of sex hormones such as oestrogen and progesterone. In particular, the increase in progesterone levels before their period can promote bloating and other digestive issues, as well as oestrogen that stimulates muscle relaxation in the gut by inducing nitric oxide synthase. Furthermore, female sex hormones can affect the processing of stimuli (discussed below); for example, during menstruation females may experience a greater perception of pain. The relationships between ovarian hormones and the gut, including gut transit and motility, the gut barrier, microbiota and the immune system, are complex, and can ultimately affect bloating via several mechanisms (Mulak et al, 2014).
The role of the gut bacteria
Our gut bacteria (or microbiota) are responsible for breaking down otherwise undigestible foods, such as dietary fibres, in our gastrointestinal tract. In the large bowel (or colon), these non-digestible carbohydrates are digested by the gut bacteria by a process called fermentation, which produces short-chain fatty acids (acetate, propionate and butyrate) as well as gases as a by-product. These gases are mainly hydrogen and carbon dioxide, but sulphur and methane-containing gases are also produced by some bacteria.
Abnormal numbers and types of bacteria have been found in patients with gastrointestinal diseases such as IBS, as well as in other health-related conditions such as obesity, and may explain why more bloating is observed in such cases. For example, these patients may have a greater proportion of methane-producing bacteria living in their large intestines.
Gastrointestinal diseases associated with bloating:
Inflammatory bowel syndrome (IBS)
IBS is a condition that affects 10% of us in the UK and bloating is the second most common symptom reported by IBS patients. IBS is an umbrella term for a range of gastrointestinal symptoms, including bloating and changes in bowel habit, but unfortunately cannot be diagnosed directly and, instead, is ‘diagnosed’ after ruling out other gastrointestinal disorders. In patients with IBS, dietary changes, such as drinking less alcohol and caffeine or increasing your intake of dietary fibre, (particularly if suffering with constipation), may ease some of these symptoms including bloating. However, these are very personal and differ on a case-by-case basis. More recently, there is evidence for improvements in symptoms and quality of life in IBS patients after following the Low FODMAP Diet. FODMAPs are a group of carbohydrates found in foods such as wheat, beans, cow’s milk and some fruits and vegetables e.g. cauliflower and apples, that can aggravate symptoms, particularly bloating, in IBS patients. For more information on IBS, FODMAPs and the Low FODMAP Diet, please go to: https://rhitrition.com/irritable-bowel-syndrome/.
Constipation is defined as passing less than 3 bowel movements per week, having hard stools, difficulty passing stool and/or not feeling empty after bowel movement (NHS, 2020). The delay in passing stool and increase in stool bulk leads to the accumulation and trapping of gasses and thus bloating. Furthermore, this is exacerbated by the longer time spent in the large bowel, which increases bacterial fermentation and the production of gasses.
Small intestine bacterial overgrowth (SIBO)
Most of our gut bacteria live in our large intestine, where they breakdown undigestible foods. Small intestine bacterial overgrowth (SIBO) occurs when some of these bacteria grow in the small intestine, where most of digestion takes place as well as the absorption of nutrients. Here, they can interfere with these processes and lead to symptoms such as bloating (Dukowicz et al, 2007).
In the last 20 years or so, evidence has emerged for a condition called visceral hypersensitivity which describes a lower threshold, or greater sensitivity or perception, to bloating or other gastrointestinal symptoms such as abdominal distension or pain (Azpiroz, 2002). This can result from various mechanisms, from the sensing and detection of stimuli by receptors, to the transmission of these via nerves, and to the responses to these stimuli such as pain. Patients with gastrointestinal disorders are particularly prone to suffering from visceral hypersensitivity.
Other gastrointestinal disorders
Coeliac disease is an autoimmune disorder where individuals are not able to absorb gluten found in wheat, rye and barley. Eating gluten leads to an immune response that damages the small intestine, preventing nutrient absorption. These patients have to avoid foods with gluten (i.e. eat gluten-free foods) to prevent symptoms such as diarrhoea, bloating and abdominal pain. In these patients, bloating is one of the most common symptoms, both in those following a gluten-free diet and those not on a gluten-free diet (O'Leary et al, 2002). Bloating is also a symptom of inflammatory bowel diseases (IBD- not to be confused with IBS), namely Crohn’s Disease and Ulcerative Colitis (UC), which affect over half a million people in the UK (Ghosh & Premchand, 2015). In these disorders, long-term (chronic) inflammation is observed in the gut, and in UC ulcers develop in the large intestine.
There is no real ‘one size fits all’ treatment plan for bloating, and these tend to be personalised and range from lifestyle changes (e.g. diet, exercise and stress) to administering probiotics and medications such as charcoal, laxatives or even antibiotics (Lacy et al, 2011). Identifying the potential cause of the bloating is particularly important to allow for addressing underlying conditions, for example dietary issues in patients with food intolerances or with IBS. If the bloating is being caused or exacerbated by stress, then this is something important to tackle. For example, by starting with identifying, and addressing, the trigger of this stress, or practising stress-relievers such as meditation and exercise. Being mindful about the way we eat, for example eating calmy and chewing carefully, may also reduce gas inhalation and improve digestion, consequently preventing bloating. Exercising after eating and drinking water can also help digestion and prevent water retention and bloating.
Take home message
Bloating is a very common gastrointestinal symptom and can be triggered by a wide range of factors from diet to stress. Although many of us experience bloating intermittently and this is fairly normal e.g. after eating a meal, it is important to see your GP if this is persistent to rule out any gastrointestinal disorders such as IBD. Removing (or adding!) specific foods or food groups is not necessarily a treatment for bloating, unless of course you have a food intolerance. Keeping a food diary is a great way to record your symptoms and to help identify any food-related triggers. It is best to make an appointment with a Registered Nutritionist or Dietitian before altering your diet to deal with gut-related issues such as bloating.
This post was written by Dr. Fiona Malcomson BSc (Hons) MRes PhD. Fiona is a Research Associate at Newcastle University with a PhD in Molecular Nutrition and is also currently undertaking a Clinical Nutrition MSc at the University of Aberdeen. Fiona’s primary research interest is exploring the relationships between diet and other lifestyle factors, such as adiposity and physical activity, and markers of large bowel health and of bowel cancer risk. Her research investigates the underlying mechanisms behind these relationships. Fiona is passionate about breaking down complicated science so it’s accessible for everyone and contributing to evidence-based nutritional and lifestyle public health recommendations through her research. You can find her on Instagram @Fiona.Malcomson and twitter @FionaMalcomson.
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