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Why Does Gas Cause Bloating?

One of the most discussed subjects in practice involves the painful and disruptive effects of trapped gas in the bowel and the excessive releasing of ghastly embarrassing gas.

I am going to have to take a walk through some physics and anatomy & physiology to explain this one! Perhaps a cup of tea would be a good idea for this blog!

Your bowel is the last part of a muscular tube that makes up the digestive tract (gut). The digestive tract is around 9 meters long, and the last (approx.) 1 ½ metres is the bowel. This is also called the large intestine, large bowel, or colon.

The bowel is porous and absorbs water and water-soluble nutrients. As this water is absorbed, the insoluble residue, which includes lots of bacteria, forms into solids (poop).

These solids should be soft enough to pass out of your bottom comfortably, easily and without straining.

When this process is disrupted for any reason, the first thing that happens is water is overly absorbed from the insoluble waste, and the insoluble waste matter dries out.

Your brain/bowel doesn’t recognise that this waste is already drier than it should be; your bowel just keeps drawing water off. The result is that the waste matter gets drier and drier and then harder and harder. This matter forms into round balls due to the tubular shape of your bowel. These are uncomfortable and hard to squeeze out when you go to the toilet; they just do not travel to the exit easily.

Lots of bacteria populate this fibrous matter, and when you put large amounts of fibre in a warm, dark environment, add in some sugars and bacteria, you pretty much turn in to a very efficient compost machine. This creates lots of gas which can only be excreted through your bottom.

Depending on what you have eaten and how long it’s been hanging around in your bowel will depend on what it will smell like. Add into the mix various levels of anxiety, which stimulates adrenaline, and things can get very smelly and sometimes downright offensive and embarrassing.

Now to the physics, I have broken this down to give an overview of what you might feel and identify with, following your personal bowel experiences.


Solids take up a finite amount of space; this means they do not expand.

Insoluble waste matter contains lots of water as it passes into your bowel. As it travels along the bowel, excess water is absorbed back into the body.

Drawing too much water from waste that is congested from the insoluble waste in your bowel forms into hard solid pellets.

But, solids don’t expand in size, so when they are moving through your bowel, although it may make you feel full and uncomfortable, they don’t really cause too much trouble until you try and pass them out of your bottom.


Like solids, liquid also takes up a finite amount of space, but liquid molecules like to lie as flat as possible. For example, a litre of water only ever takes up the same amount of space, whether it’s in a glass or a saucepan. The liquid in your bowel does not really feel uncomfortable, and we are not really aware of it unless we are suffering diarrhoea-type symptoms.


This is the bit that causes significant pain and distress.

Gas molecules like to get as far away from each other as possible. You can see this with steam which contains gasses combined with water. Boil the kettle, and you will see the steam gets everywhere. It is a visible image of how gasses like to expand.

When gas forms in your bowel (which is perfectly normal and natural,) if everything is working well, we naturally pass it out of our bodies as we move around (exercise) or when we use the toilet.

But, when we get a build-up of waste matter, we produce more gas, which, if you are congested and constipated, can build up pressure, and this situation becomes self-perpetuating.

The more gas we produce, the more the molecules want to expand away from each other, creating pressure against the bowel wall. Nerves and pain receptors pick up this pressure exerted against your bowel wall, and you feel the pain and discomfort we can all identify with.

Imagine a balloon.

Blow it up a little, and the balloon feels soft; the more gas you put into it, the tighter and more pressured it becomes. Too much gas and it puts the balloon under high pressure as the gas molecules try to get away from each other.

Your bowel is very similar. The gas molecules put your bowel under pressure as the molecules try and expand; this, in turn, creates pain, bloating, and an abdomen (tummy) that can feel as tight as a drum. As the gas travels along your bowel, the bowel wall experiences variations of pressure which cause you to feel more pain and discomfort.

What can help with this congestion and build-up of gas?

By releasing the build-up of waste matter and associated gas, the abdomen can return to its normal size, which should feel soft and malleable to the touch. It should not feel hard, sore or painful when touched.

Colonic hydrotherapy can really help by releasing this waste, aided by taking a high-quality supplement of friendly bacteria, which help break your food down properly in your bowel and help keep the less beneficial bacteria under control.

Sometimes altering your diet is needed. It can also help by reducing highly fermentative food for a time. These foods are referred to as a low FODMAPS foods.

Increasing fluids can also help as we need plenty of water to keep the insoluble fibre and waste matter soft and wet. This needs to be kept constant for the best results.

If you have any concerns about your bowel or gut health, see your GP.

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