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What happens when I fart © Getty Images

Why do I fart so much? The science you never knew you wanted to know about flatulence

Published: 04th April, 2022 at 16:00
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Where do farts come from, and what happens if you hold it in? Does everybody fart – and what about animals?

Everybody burps and farts around 2.5 litres of gas per day, which comes from the air we breathe, the drinks we quaff and the bacteria in our digestive system. Our bodies get rid of this excess gas via the mouth and anus. You may not even notice yourself passing gas – it can be very small quantities, and sometimes doesn't smell at all.

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Unlike in cows, methane is not a major constituent of our farts. So if someone sets a fart alight, it’s usually hydrogen gas that’s burning.

While farting is completely normal, if you start to fart more than normal, if can be the result of an underlying medical condition.

Why do we fart?

We fart because there is gas in our intestines that we need to get out.

A small amount of swallowed air makes it into the intestines, but most of the gas there is produced by the bacteria that help to digest our food. This gas is expelled by burping and farting.

The gas is mainly hydrogen and carbon dioxide. The smell comes from sulphur compounds that are only present in trace amounts.

The nerve endings in your anus allow you to distinguish between a build-up of gas and a solid stool, so you can pass wind safely.

Does everybody fart?

Without exception. Gas ends up in the large intestine from air that is swallowed and from the action of the bacteria that live there. It is mostly nitrogen and carbon dioxide with some hydrogen and methane mixed in, with tiny amounts of skatole, indole, methanethiol, hydrogen sulfide and dimethyl sulfide to give it a stinky smell.

Everyone farts but some people take enough care with the release that they are rarely caught out. – Hannah Ashworth

Read more about flatulence:

Why do I fart so much?

It's normal for some people to fart more than others. According to the NHS, the average person farts between 5 and 15 times a day. However, there are a few conditions that can cause you to fart more than normal.

Farting is a symptom of both coeliac disease and lactose intolerance. As well as eating foods that are difficult for you to digest, excessive flatulence can be caused by constipation, irritable bowel syndrome, indigestion and gastroenteritis. It can also be a side effect of some medications.

If you're concerned about your farting, visit your GP.

If you hold in a fart, where does it go?

Holding in a fart
What happens if you hold in a fart? © Getty Images

It stays right there! If you suppress a fart, it actually just seeps out more quietly, or you might be able to hang on until the next time you are on the toilet. But sooner or later, that fart is coming out! – Luis Villazon

What foods make you fart?

Beans, beans, they're good for your heart. The more you eat, the more you fart... or so the poem says. But why do beans make you fart, exactly?

Beans, like many other foods, contain plenty of soluble fibre. While this is great for your health, it can also make you fart – soluble fibres are fermented in the colon, rather than being digested in the intestines. This produces gas, which becomes a fart.

Other fart-inducing foods include pulses, such as lentils and peas, brassicas including cabbages and broccoli, onions, prunes and apples.

Do animals fart?

So, all humans fart – but does that mean all animals do, too? Read on to find out which are flatulent fiends and which are silent but deadly.

Do rabbits fart?

Yes. Rabbits are described as non-ruminant herbivores, which means that while their diet consists of plant matter such as grass, flowers, as well as twigs, they do not have a specialised stomach to digest plant material. Instead, they rely on microorganisms (bacteria and protists) within their caecum (a pouch in their large intestine: you have one too) to extract nutrients from their cellulose-based diet.

Since their food is initially digested in their large intestine, in order to get the most nutrition out of their food rabbits also reingest their cecotropes, which are soft faeces consisting of the fermented plant material.

Unsurprisingly, both the rabbit’s slightly disgusting diet and their digestive system provide the perfect recipe for farts. Rabbits not only can and do fart, but they need to fart. Stress, dehydration and a diet that is low in fibre but high in carbohydrates and sugar can lead to a build-up of gas within their intestines, which is known as intestinal stasis.

While farts are often humorous, this is no laughing matter for rabbits, as this gas build-up is extremely painful and can become fatal very quickly unless properly released, sometimes requiring medical intervention. – Dani Rabaiotti

Do spiders fart?

Nobody knows! Spider flatulence is an oddly understudied topic in scientific literature, but we can look to their digestive system for some clues. Spiders do the vast majority of digestion outside their body, injecting their prey with venom from their fangs before ejecting sputum, full of digestive enzymes, from their mouths, through the fang holes and into the body of their prey.

They then wait whilst the digestive juices break down tissues inside the exoskeleton or, in some cases, skin of their prey. Spiders will then suck up the liquidy goodness into their mouths and stomachs, then they regurgitate it and eat it again.

This happens a number of times, as spider digestive systems can only handle liquids – which means no lumps! It would seem likely that spiders ingest air during this process – one of the key elements needed for a fart. Once they have extracted all the nutrients, in an organ called the ceaca, the food passes to the stercoral sac, where the moisture is extracted before anything left over is excreted through the anus as waste.

Since the stercoral sac contains bacteria, which helps break down the spider’s food, it seems likely that gas is produced during this process, and therefore there is certainly the possibility that spiders do fart. No work has been done to verify this to date, however, so the truth remains a mystery until urgently needed research funding is allocated. – Dani Rabaiotti

Do birds fart?

Birds have an anus, and so technically could fart, but to date there’s been no official evidence that they do. One theory is that they don’t need to fart like humans and other mammals because they have a faster rate of digestion – their food simply doesn’t spend long enough in their short gastrointestinal tracts to ferment and form gas.

Another theory is that birds’ guts don’t contain the same gas-forming bacteria as mammals. It’s also possible that ornithologists have missed bird farts because they leak out passively rather than in one eruption, or birds could be burping to release unwanted gas instead. – Charlotte Corney

Did dinosaurs fart?

Yes! Just like dogs, some insects, and even millipedes, dinosaurs undoubtedly would have passed gas.

Not only did Brontosaurus and Triceratops make wind, but they would have made a lot of it. So much, in fact, that it affected the entire Earth and its climate. One study found that dinosaurs’ ‘emissions’ were an important factor in keeping the planet warm and moist during the Mesozoic Era (250 to 65 million years ago).

Similarly, farts and burps shape our modern climate: emissions from livestock account for more than 10 per cent of all anthropogenic greenhouse gas emissions today. – Dr Stephen Brusatte

Read more about how the body works:

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Authors

Sara RigbyOnline staff writer, BBC Science Focus

Sara is the online staff writer at BBC Science Focus. She has an MPhys in mathematical physics and loves all things space, dinosaurs and dogs.

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