Poo Or A Fart? Here's How Your Body Knows What's Coming

Although we can be occasionally caught out, we can almost always tell when what we feel brewing in our body is a fart or a poo – but how do our guts know the difference?

Fortunately, the Zoe Health Study has answered our burning question about our bottoms.

Dr. Will Bulsiewicz, ZOE’s U.S. medical director and a board-certified gastroenterologist explained to the team in a blog post that we can thank our ‘poop reflex’ for preventing any embarrassing accidents in public.

“When the rectum fills beyond a certain capacity,” Dr Bulsiewicz shares, “the rectal walls are stretched, triggering the defecation cycle. This begins with the rectoanal inhibitory reflex [RAIR], where the internal sphincter relaxes.”

To break that down for you a little more – your internal anal sphincter works hard to stop anything sneaking out your butt and is involuntary, your external sphincter is the one you can squeeze and control.

So what next? According to the doc, “this RAIR reflex is thought to allow a small amount of rectal contents to descend into the anal canal, where a specialised mucosa samples whether it is gas, liquid, or solid.”

Okay, time for some more explaining into simple terms: mucosas line the insides of some of your body’s organs and, helpfully in this case, your anal canal.

Mucosas contain glands which release, you guessed it, mucus. Dr Bulsiewic explains that this special mucosa in your anal gland can sample what’s going on and tell your body if it’s gas or poo (and whether it’s safe to release).

But how does it do this? Well, scientists don’t actually know – some think that because your anal canal is sensitive to temperature, this might be the key in deciding what you’re producing.

Your anal canal is also full of sensory nerve endings, so the consensus is that the mucosa takes a sample, these nerve endings are alerted, they decide what they’re dealing with and voila, you can decide whether to sneak a fart or run to the loo.

You can read the full breakdown here.