Why Do Beans Make You Fart?

Farts are definitely funny. We think we’re pretty clever and sophisticated beings with art and science and civilisation and then all of a sudden some smelly gas comes noisily out of our bottoms. For a moment all of that sophistication is stripped away and we are abruptly reminded of what we truly are; like any other animal we are leaky bags of meat and this realisation is hilarious.

Pico, one of Letterbox lab's assistants with a pink cloud of fart coming from behind him. Meg looks on in shock.

For a child to be curious about our most humorous of bodily functions is not only natural but to be celebrated. Curiosity about what comes out of our bodies can lead to a deeper understanding of our bodies and what we put into them. So let’s ask,why do we fart and why do some foods like beans make us fart more?

The gas that you pass can come from two different places. Firstly there’s air that you have swallowed while swallowing your food and secondly there’s gas produced from the digestion of your food. The first of these has little to do with the type of food you eat and more to do with the way you eat it. The second type is affected by your diet and what type of bacteria live in your gut.

So, let’s talk a little about how digestion works. Food is a collection of molecules, most of them are very long molecules. After food passes through your stomach into your small intestine those long molecules get broken down into smaller ones. The smaller ones get absorbed through the lining of the intestine into the blood.

But there are some types of food molecules which the small intestine cannot break down, including fibre and oligosaccharides. Beans, lentils, chickpeas and the other musical fruits are full of both of these types of molecules.

These molecules pass through the small intestine undigested and get to the large intestine. They provide a veritable feast for the inhabitants of your large intestine which contains about 100 trillion bacteria. That’s greater than the number of human cells in your bod. The intestine is also a complex ecosystem with over 1000 different species. That level of biological diversity in such a small space would put a rain forest to shame!

When we eat beans lots of undigested food molecules make their way to these little guys who break it down through fermentation. Fermentation produces gasses – carbon dioxide, methane, hydrogen, hydrogen sulphide. These gasses build up inside us and we must depressurise through one hole or another. Many large herbivores digest their food mostly through bacterial fermentation. Zebras, for example, become so gassy that the first thing they do when they see a predator is let one rip so they are less bloated for the impending chase.

The rear view of several zebra

So science does back up the popular rhyme about beans. Different foods will indeed affect how much your bottom burps. We like to encourage at-home experiments here at Letterbox Lab, but I’ve a feeling this would not be a popular suggestion.

Would you like to spend time with your children doing something that’s fun and educational for them and hassle-free for you?

Letterbox Lab is a monthly science kit that arrives through your letterbox containing everything you need to perform incredible experiments with your children.

Your children will love it. It’s colour changing, fizzing reactons, slimes, things that glow in the dark, making helicopters and catapults. All with beautifully illustrated comic-style instructions that they will actually enjoy reading.

You’ll love it because it’s so easy. It just arrives at your house with everything you need to do all the experiments. Unlike other science kits there’s no looking in the back of cupboard for cream of tartar or figuring out where you can buy propanol on a Sunday afternoon.  You just open the box and get started with ease.

Find out more about our unique series of science kits here 

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