Why Do Farts Smell?

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The main reason fart smell is because of the type of food people eat. If someone eats a lot of protein-rich vegetarian food, the byproducts of digestion will include sulfide compounds, which have a strong, unpleasant smell. Non-vegetarian food can also contain sulfur, which contributes to bad-smelling gas. Carbohydrate-rich food is usually less smelly, but can cause more gas.

The gut houses billions of bacteria that break down the food you swallow into smaller and smaller parts in order to absorb its nutrients. This process generates a myriad of gaseous byproducts, depending on the nutrients the food contains.

“Oh god,” you think, “not now, not on public transport”. You try to suppress it, but it’s overbearing. You admit defeat. The beast must be unchained from the dungeon, but he must be freed slowly in silence.

You strategize: “I will look out the window or pretend to check my email while the beast escapes tentatively on its toes, stealthily behind the veil of my pretense. I must not draw any suspicion, and must appear as innocuous as a streetlight, without a hint of any sheepishness.” You feel ashamed, but, admittedly, slightly proud and certainly relaxed. “Well done, my man.”

People around you seem distraught. Someone anxiously performs the sign of the cross while someone else jumps out from the bus. In this chaos, people look at you in disgust and disdain. The environment has grown toxic, literally. It stinks of rotten eggs, but how do they know it was you? The current song ends and the next begins. You forgot you were wearing earphones. You try to be awkwardly facetious: “He who smelt it dealt it?”

No one around just a quick little fart man i hope no one comes to my desk meme

We fart 10-20 times per day, but not every fart is made equal. While some, as the rule goes, are loud and alarming, but not noxious, and the silent ones might save you the public shame, they might not save yours and the public’s nostrils – they can be deadly. Why do some farts some smell and others don’t?

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You Fart What You Eat

The medical term for a fart or “wind from the anus” is flatulence. Flatulence or excess intestinal gas is primarily caused by the digestive system. Much of its volume is comprised of gases like methane, hydrogen and carbon dioxide. However, the gut is not its only source. A considerable share is also comprised of oxygen and nitrogen, gases that we swallow throughout the day. Still, the latter’s contribution is minimal compared to the former. It is the gut that dominates the production of gas. This is why the properties of this gas, whether odorless or noxious to the verge of nausea, depend on the food that goes into the gut. The food you eat influences bacteria in your gut and therefore affects your farts.

The gut houses billions of bacteria that break down the food you swallow into smaller and smaller parts in order to absorb its nutrients. This process generates a myriad of gaseous byproducts, depending on the nutrients the food contains. When gut bacteria operate on protein-rich vegetarian food, such as broccoli, sprouts, cauliflower and cabbage, the byproducts include sulfide compounds, such as hydrogen sulfide, as these veggies are replete with sulfur. It is the presence of sulfide compounds in a fart that wreaks havoc and drives everyone out of the room.

Refrigerator vegetable fruit
The coal to your steam engine.

Garlic, nuts and onions, items that have gained a nefarious reputation for causing bad breath, don’t disappoint at the other end of the tube either. On the non-vegetarian shelf, sulfur is found in eggs, red meat and fish. It is the glut of proteins bodybuilders consume that leads to them so often being accused of contaminating gym air.

On the other hand, when food rich in carbohydrates is broken down, the result is a bunch of gases that are usually odorless. However, while the consumption of carbohydrates might not force you to discharge a pungent stench, it certainly might increase the frequency of passing gas dramatically. This is because carbohydrates pass through the small intestine without being properly digested. Instead, they are fermented by the bacteria in the large intestine. It is this malabsorption that leads to excess gas.

cup of milk
Credits: Sea Wave/Shutterstock

This is why people who are intolerant of certain nutrients often have a disturbed gut. Their system lacks enzymes that allow them to digest a particular nutrient – they have no option but to shift the rest of the bacterial party to the large intestine. The most popular of such misfortunes are lactose and gluten intolerances. The former is worse because dairy products are rich in sulfur.

Also Read: Can Farts Be Set On Fire?

It’s Okay To Fart

There seems to be a compromise at play here: if you wish to get rid of the pungent smell at the cost of more odorless farts by consuming more fiber, you will end up lacking protein. However, if you snub quality over quantity, you might end up constipated. Without any fiber, your intestinal machinery will be subject to rust and jamming.

So, yes, the healthier you eat, the worse the stench is that you exude. Perhaps this is reasonable. To achieve optimal intestinal health, one must feed its bacteria the food that boosts health and effectivity. The degree of intensity also varies from person to person – every individual’s flora of bacteria is endowed with different capabilities, rendering his gas mild or excessively stinky.

Love is like a fart if you have to force it, its probably crap meme

Is passing gas therefore a sign of good digestion? Yes and no. One must draw a line where the stench might be perceived by its audience as outright horrible. If you’ve been wondering lately if your gas is too smelly, or perhaps you’ve suddenly become an everyday recipient of contemptuous staring on the bus, subway or even the most non-judgmental circle of your friends, it might be time to seek a professional, or friends!

Also Read: Why Does Some Poop Float While Others Sink?

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References (click to expand)
  1. Intestinal gas Causes - Mayo Clinic. The Mayo Clinic
  2. Why Do My Farts Smell So Bad? - Health. Health
  3. What is The Role of Gut Bacteria in Human Health? | Eufic. eufic.org
  4. flatulence | Health Topics - NutritionFacts.org. nutritionfacts.org
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About the Author

Akash Peshin is an Electronic Engineer from the University of Mumbai, India and a science writer at ScienceABC. Enamored with science ever since discovering a picture book about Saturn at the age of 7, he believes that what fundamentally fuels this passion is his curiosity and appetite for wonder.