How Are Farts Made?

February 19, 2023 Emma Keenan Dietitian

Farts, all fun and games until someone gets Dutch ovened.

For most people farts are a normal part of everyday life and can either be embarrassing, get a giggle, or evacuate a room. For others, flatulence can cause distress and discomfort and may be associated with abdominal pain, belching, bloating, and excessive gas production. These symptoms can have a negative impact on a person’s social well-being.

What is gas?

The majority (99%) of intestinal gas is composed of hydrogen, carbon dioxide, and methane, all odourless gases. Are you wondering which gas is responsible for those stinky farts? That would be sulfur-containing gases. Stinky farts generally occur from eating animal foods that contain amino acids such as red meat, poultry, milk, eggs, and cheese.

Where does gas come from?

The gas that comes out of your rectum has four possible sources

Air that has been swallowed while eating or drinking
Carbon dioxide from the interaction between stomach acid and alkaline secretions or food
The result of bacterial fermentation produces hydrogen, methane, and carbon dioxide
Gas from the bloodstream that moves into the GI tract

How can gas be eliminated from the GI tract?

Intestinal gas is eliminated via 3 pathways:

As farts through the anus
Absorbed into the bloodstream and exhaled via the breath
Gut bacteria further metabolise it into non-gas products

A study found that 23% of gas is eliminated via pathway no. 1 and the remaining 77% is eliminated via pathways 2 and 3.

What is normal?

A study by Thomlin, Lowis, and Read sort to answer this question. They collected gas from 10 healthy volunteers (5 men, 5 women) over a 24-hour period. How you may wonder! Jar? No! Participants’ farts were collected in a plastic bag via a rectal catheter. The collection began after they had emptied their bowels. They were put into two groups one that ate their normal diet + 200g baked beans and the other who consumed only a fibre-free nutritional supplement drink.

The results:

Men and women expelled similar amounts of gas
Participants produced between 476mL and 1491mL of gas
The more fibre you eat the more farts you produce
Larger volumes of gas were produced after eating
Farts produced at a faster rate contained more fermentation gases
Lesses volumes were passed overnight
The fibre-free diet group produced less gas

Which foods are associated with farting?

Foods that are associated with intestinal gas production are those high fibre foods including fruits, vegetables, legumes, and whole grains. These foods tend to be high in short-chain carbohydrates; these are not digested or absorbed in the small intestine. Thus they make it intact to the large intestine. Here they either attract water or are fermented by gut bacteria producing large amounts of gas. These processes can trigger uncomfortable symptoms in some people.

FODMAP is an acronym for these sugar molecules

Fermentable

Oligosaccharides

Disaccharides

Monosaccharides

and

Polyols

What can we do about excessive gas production?

For people with irritable bowel syndrome who experience distressing symptoms associated with increased gas production a 3-phase FODMAP diet can be implemented.

Phase 1 is the elimination of high FODMAP foods
Phase 2 is the reintroduction of FODMAPs to find trigger foods
Phase 3 is personalising the diet to ensure that it includes as many FODMAP foods as possible

For everyone else, if you are introducing more fibre-containing foods into your diet it is a good idea to start slow and don’t give up.

It has been found that the rate of gas elimination from the GI tract is not static and can be influenced by diet. For example, when people first start consuming legumes gas production increases resulting in more farts. However, with regular consumption, after 2 weeks fart volumes go back to pre-legume consumption levels. It is thought that over this time elimination is increased through the breath and gut microbiota pathways.

I will leave you with some childish wisdom, Beans, Beans, the Musical Fruit

Beans, beans, they give you gas

They make you fart, and burn your ass

The more you eat, the more it hurts

So slow down your eating to stop the squirts

Beans, beans, the musical fruit

The more you eat, the more you toot

The more you toot, the better you feel

So we have beans at every meal!

Beans, beans, they’re good for your heart

The more you eat, the more you fart

The more you fart, the more you eat

The more you sit on the toilet seat

Melbourne Dietitian & Nutritionist