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Ask A Dietitian: How Much Gas is Normal?

This series digs into the what, why and how on all your gut-related questions. Today we're talking gas with Gastroenterology Dietitian Dr Sammie Gill. Diving into what gas is, what causes it and how you can help manage it.

What is gas?

Gas, wind, flatulence, flatus, farting – they all mean the same thing! And while it’s normal, excess gas can be a symptom of a gut-related disorder.

So let’s start with some basic facts – it’s thought the average person passes gas 10-20 times per day, equating to 0.4-1.5 litres of gas (Modesto et al 2022).

The gas you pass is a mix of different gases, mainly nitrogen, oxygen, carbon dioxide, hydrogen and methane. They make up over 99% of all gut gas and are completely odourless.

It’s actually less than 1% of gases that cause the characteristic ‘rotten egg’ smell - these are made up of odorous sulphur-containing gases, such as hydrogen sulphide (Kalantar-Zadeh et al 2019, Mutuyemungu et al 2023).

Why does it happen?

Gas comes from two main sources – from the outside (the air you swallow) or from the inside (through fermentation by gut microbes).

Gases produced inside the gut can take one of three routes: 

  1. They are absorbed across the gut wall, enter circulation and expelled by your lungs
  2. They are utilised by other gut microbes and transformed into other compounds
  3. They are expelled at the other end as gas

The number of times you pass gas, the types of gas, and the amount of gas you produce is largely due to what you eat. Though other reasons for a gassy gut include feelings of stress (which alters gut motility) and menstruation (which causes fluctuations in hormones, particularly estrogen and progesterone). 

But what makes one person pass gas will not necessarily be the same for someone else – in part, likely due to the mix of microbes in your gut (remember, everyone’s gut microbiome is different). 

Plant-based foods are known gas contributors. Why? Simply because they contain lots of different types of fibre and plant chemicals that gut microbes love. For example, legumes (e.g. peas and beans) are naturally high in galactooligosaccharides (GOS) – these are highly fermentable prebiotic fibres (quick tip: draining, rinsing, and cooking them well reduces GOS levels).

But this doesn’t mean you should be cutting plant-based foods out – it’s likely to be more harmful than helpful in the long-term, and why it’s important to work out your specific triggers.

Which foods make gas smell? The main culprits are those plant-based foods with sulphur-containing compounds. These are commonly found in Cruciferous veggies such as broccoli, cauliflower, kale, Brussel sprouts, and cabbage (as well as Allium veggies such as onion, leeks, and garlic). 

But the Cruciferous veggie group is an important one. Not only do they contain all the gut loving nutrients that microbes need, but they also contain distinctive plant chemicals, such as glucosinolates. These are thought to have protective health properties. In fact, studies have shown a lower risk of gut-related cancers with increased consumption of these veggie types.

But it’s not just plant-based foods that are responsible for the smell. Other foods that contain these sulphur-containing compounds include meat, chicken, eggs, and some alcohol (such as wine).

What can you do to improve it?

Remember, passing gas is normal and the sign of a healthy functioning gut, but people with certain gut-related disorders can have more issues with gas. If you are experiencing chronic and/or painful gas, seek support from a healthcare professional. 

Try a different eating pattern 

Eating smaller, more frequent meals is less likely to overload your gut (and gut microbes). Try four to six smaller meals during the day, rather than three larger ones.

Eat mindfully 

Practice belly breathing before you start eating – this will help to relax your gut. Also slow the pace of your eating and chew your food well (at least 20 chews per mouthful) to aid digestion. 

Avoid swallowing extra air

Refrain from drinking carbonated drinks and chewing gum – these encourage you to swallow extra air. 

Adjust your diet 

Focusing on plant-based foods is important for gut health – it will also help reduce the risk of constipation which can cause gas. Instead, find out which foods are gas-producing for you. Try keeping a food and fluid diary for 2-4 weeks to try and establish any patterns/trends.  

Trial peppermint capsules  

These are antispasmodics which have calming effects, helping to relax the muscles in your gut.  

Rule out gut-related disorders 

Irritable bowel syndrome, undiagnosed coeliac disease, and lactose intolerance are some gut-related disorders where gas is more problematic. The correct diagnosis is important for optimising management. Also, if you have other accompanying symptoms (e.g. pain, change in poo habits) see your GP. 

Try pelvic floor exercises  

This can strengthen the muscles that help you control the passage of gas. One simple exercise is pretending you are trying to stop yourself from passing gas and squeezing tightly. Repeat ten times. 

Read more from our Ask a Dietitian series:

How can I help manage chronic constipation?

NB: There is no one approach to managing gas and different approaches will work for different people. It’s often a combination of approaches that can help. For tailored advice, please seek advice from a registered dietitian.