How Flatulence Works

Learn about the causes of gas -- and not the kind you put in your car -- in this podcast from Marshall Brain.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from how stuffworks dot com. Where
smart happens him Marshall Brain, What is happening when we fart?
We all suffer from this problem to varying degrees. Where
does the gas come from? Just think about your digestive

(00:24):
system for a moment. One thing that's obvious is that
digestion involves breaking things down. Everything in food has to
be broken down into small units in order to enter
the bloodstream. Protein must be broken down into its individual
amino acids, Fats must be broken down into fatty acids,
and carbohydrates both simple and complex must be broken into

(00:46):
individual glucose molecules. Flatulence occurs when a food does not
break down completely in the stomach and the small intestine.
As a result, the food makes it to the large
intestine in an undigestested state. For example, if you are
lactose intolerant, it means that you lack an enzyme lac

(01:07):
taste in your intestine. This enzyme breaks lactose apart into
two sugar molecules so they can enter the bloodstream without lactaste.
Lactose passes undigested through the stomach and small intestine, and
it arrives in the large intestine. They're the lactose meets
up with billions of hungry bacteria, the natural intestinal fauna

(01:32):
we all have in our large intestine. These bacteria are
happy to digest lactose. They produce a variety of gases
in much the same way that yeast produces carbon dioxide
to leaven bread. Gases such as methane, hydrogen, and hydrogen
sulfide are common gases that these bacteria produce. Hydrogen sulfide

(01:54):
is the source of the odor we associate with flatulence.
Certain foods per do more flatulence than others because they
contain more undigestible carbohydrates than others. Beans, as you might expect,
are particularly well endowed in this regard. Be sure to
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(02:17):
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