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Flatulence, or passing gas,
is a normal daily phenomenon.

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Most individuals, yes, that
includes you,

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will make anywhere 
from 500-1500 milliliters of gas,

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and can pass gas ten to twenty
times a day.

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But where does this bodily gas come from?

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A small proportion may come from ingesting
air during sleep, or at other times,

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but the majority of gas is produced by
bacteria in our intestines

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as they digest parts of food which we cannot.

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Our intestine is home to
trillions of bacteria

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living in a symbiotic relationship with us.

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We provide them with a safe place
to stay and food to eat.

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In exchange, they help us 
extract energy from our food,

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make vitamins for us, like vitamin B and K,
boost our immune system,

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and play an important role in 
gastrointestinal barrier function,

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motility and the development of 
various organ systems.

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Clearly, it's in our best interest
to keep these bacteria happy.

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Gut bacteria get their nutrition
primarily from undigested food,

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such as carbohydrates and proteins,
which come to the large intestine.

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They ferment this indigested food
to produce a wide range of compounds,

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such as short-chain fatty acids,
and of course, gases.

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Hydrogen and carbon dioxide 
are the most common gaseous products

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of bacterial fermentation, 
and are odorless.

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Some people also produce methane due to
specific microbes present in their gut.

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But methane is actually odorless, too.

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Well then, what stinks?

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The foul smell is usually due to 
volatile sulfur compounds,

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such as hydrogen sulfide and
methanethiol, or methyl mercaptan.

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These gases, however, constitute
less than 1% of volume,

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and our often seen with ingestion
of amino acids containing sulfur,

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which may explain the foul smell of gas
from certain high protein diets.

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Increased passage of gas is commonly
noticed after eating foods

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with high amounts of 
indigestible carbohydrates,

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like beans, lentils, dairy products,
onions, garlic, leeks, radishes,

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potatoes, oats, wheat, cauliflower,
broccoli, cabbage, and brussel sprouts.

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Humans lack the enzymes,

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so the bacteria able to ferment 
complex carbohydrates take over,

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and this naturally leads to more
gas than usual.

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But if you feel uncomfortable,
bloated or visibly distended,

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this may indicate impaired movement
of gas along the gastrointestinal track.

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It's important not to just 
blame certain foods

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for gas and bloating and then avoid them.

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You don't want to starve the bacteria
that digest these complex carbohydrates,

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or they'll have to start eating the sugars
in the mucus lining of your intestines.

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Your personal gas will vary
based on what you eat,

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and what bacteria are in your gut.

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For example, from the same starting sugar,

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the bacteria clostridium, produces
carbon dioxide, butyrate and hydrogen,

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while propionibacterium can produce
carbon dioxide, propionate and acetate.

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At the same time, methanogens
can use hydrogen and carbon dioxide

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produced by other bacteria
to generate methane,

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which can reduce the total volume of gas 
by using up hydrogen and carbon dioxide.

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So there's a complex web among
intestinal bacteria

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allowing them to flourish by either
directly consuming undigested food,

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or using what other bacteria produce.

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This interaction largely determines
the amount and type of gas produced,

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so gas production is a sign
that your gut bacteria are at work.

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But in some instances, people may
develop abnormal increased flatulence.

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A common example is lactose intolerance.

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Most individuals have the enzyme for
breaking down lactose,

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a sugar present in milk and
milk-derived products.

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But some people either lack it entirely,
or have a reduced amount,

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such as after a gastrointestinal infection,

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so they're unable to digest
lactose products and may experience cramping,

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along with increased flatulence 
due to bacterial fermentation.

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But remember, most gas is produced

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as a natural result of bacterial 
fermentation in the intestine,

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and indicates healthy 
functioning of the gut.

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The amount and type can vary based on your
diet and the bacteria in your intestine.

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Exercise social courtesy while passing gas,
and do try to forgive your bacteria.

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They're only trying to be helpful.