Let’s talk about gas (part 1)

Given the popularity of our son's comment about his father's farts (cf. my experience of the volcano), I decided to write a short post about these famous digestive gases.

Not only those of @lemouth, don’t be afraid, but those of everybody! ;)

Considering that at 6 years old, Zachary is a little too young to take part to an experiment on fermentation, I will restrain myself with standard biological explanations.

---

Let's start seriously: a little reminder on the notions of digestion

The process of digestion begins even before we ingest food: the smell or sight of food and the feeling of hunger prepare the body for digestion by the secretion of saliva and gastric juices.

There are two types of digestion: mechanical and chemical.

Mechanical digestion takes place mainly in the mouth and the stomach: chewing, grinding, mixing and the contractions of the digestive system (also known as tract) allows for the fragmentation of the food into a kind of porridge which will enable other actors to do their job better ...

Chemical digestion occurs throughout the path taken by the food inside the tract: saliva, hydrochloric acid in gastric juices, bile secreted by the liver... The enzymes produced allow the food to be degraded in its simplest form: nutrients. It is in this form that it can then be assimilated by the organism.

---

The very important role of the large intestine

Did you know that the intestinal flora has a weight of about 1.8 kg? It comprises on average 10.000 billions bacteria grouped into 400 species! It consists of an entire little world down there!

But what the hell are these bacteria used for?

With the recent technologies, we started to learn a lot more about the intestinal microbiota, and its role seems much more complex than we thought. Contrary to the general idea, it is used not only for digestion, but also for the development of the immune system and the nervous system.

Some studies even link gut bacteria dysfunctions to the development of some neuropsychiatric diseases! Interesting certainly ... but a little far from @lemouth’s farts !

---

But hey, why do we have gases?

In the last portion of the small intestine and in the large intestine, all the nutrients have not yet been absorbed and there are still many useful things left for the body.

The bacteria of the intestinal flora here ensure the fermentation of certain food residues that are not yet digested. It hence facilitates the assimilation of nutrients thanks to a whole set of enzymes that our own organism does not produce by itself. They also participate in the synthesis of some vitamins and allow to absorb fatty acids, calcium, magnesium, etc.

During this fermentation process, gases are produced, in particular with the treatment of carbohydrates and proteins which have not been assimilated in the stomach. You will be pleased to know that the gases emitted during this fermentation stage are composed mainly of carbon dioxide (CO₂), hydrogen (H₂) and a small portion of methane (CH₄)!

Yes, farts are full of natural gases, even if I doubt they can be used as a source of energy! Anyway, with an average emission of 0.5 to 2l of gas per day (about 12 to 25 farts), I doubt that we can do anything with this! Cows are much more productive and release, for instance, 26 million tons of CO₂ equivalent per year in France!

---

Ok, it's natural, but why does it stink?

During the fermentation process of some foodstuffs, small quantities of sulphides and mercaptans can be produced: these gases are those giving farts their characteristic smell. If the ingested food is rich in nitrogen and sulfur, the smell can then be... very strong.

Here are some foodstuffs that are associated with a high production of sulphides and mercaptan:

• Animal proteins such as meat and offal
• Seafood, fish and eggs (rich in sulfur-containing amino acids)
• Some vegetables such as garlic, shallot, cabbage, asparagus ...
• Oleaginous fruits (hazelnuts, walnuts, almonds ...)

Of course, each of us has a personal sensitivity to certain foodstuffs ... It is up to you to investigate that on your side and to share your results!

To be continued…

References: 1, 2, 3 , 4, 5, 6, 7