Why do beans make you fart?

Was reading a question about sneezing and came across this one as a link. Makes a good reading and informative as well, in case you don't find it funny.

Why do beans make you fart?

Hippocrates said, “Passing gas is necessary to well-being.” Yup, farting is a perfectly natural and unavoidable bodily process and most people produce between 1 and 3 pints per day. But why, oh, why do we do it? Let's see....

We are not alone- around 200 different species of bacteria lurking in your large intestines and bean induced farts are down to these millions of tiny friends in our guts. So what is happening?

Well, when we eat beans, or cabbage, or any other gassy food, it all gets mushed up in our stomach and is passed into the small intestine. Now, the types of sugar found in beans are a bit big to be taken into the body through the walls of the small intestine and we have no enzyme to break them down into more manageable chunks. This means it all ends up in our large intestine where all the bacteria tuck in and start to reproduce to take best advantage of all the yummy food. Unfortunately for us, gas is produced by the bacteria during the breakdown of their dinner - carbon dioxide, hydrogen and some methane is released and escape the body via the only opening available to them. These gases don't smell much, but methane and hydrogen do burn pretty happily, which is why farts can be set alight. However, this is NOT recommended as the gas can ignite backwards up your bum, burning all the trapped gas in your rectum and scorching you in the most painful way imaginable. Imagine having to explain that to the A & E nurse.

On top of all the bacterial gas, some fart gas comes from air that you have swallowed - you'll swallow more if you gorge yourself to fast rather than carefully munching your food. A lot of the gas will be absorbed into the body but in times of stress we tend to rush food and air through the body a bit fast and this makes the farting situation worse. Finally, chemical reactions between stomach acid and intestinal juices can also produce carbon dioxide that bulk out our farts.

But why are farts stinky? While gas produced by bacteria tends to be in fairly small quantities, it can be especially stinky if you've been eating sulphur containing food, such as cabbages: this is a cause of the silent but deadly warm farts in case you're interested. Hydrogen sulfide gas and mercaptans are sulphur containing fart components, and even in small amounts are not pleasant. Nitrogen containing compounds such as indole and skatole also add to the characteristic aroma of a fart. Skatole, by the way, happens to be evolutions mighty plan to stop us from eating our own poo, but that is another story.

Fart myths include the belief that women fart less than men. They don't- they just don't tend to enjoy farting in public as much as men. Also there is the claim made by some people that holding farts in is dangerous to the health. This is also a lie but holding them does mean that as soon as you relax you will release all the gas and this could be upsetting if you nod off on the train.