Alright, let’s face it: animals—and people—pass gas, either by belching or farting. But some are more gassy than others. Cows, for example, give out so much methane gas that some suspect them as one cause of global warming. Ever wonder why this might be?
Well, this science column offers some insights.
Greenhouse Gas Scare
All kinds of chemical processes go on during digestion, with complex food molecules being broken down into simple elements the body can absorb to use as energy. Certain chemicals—the acids in the stomach—play an important role in this breaking down process. But microbes also play a key role, breaking apart molecules the stomach acids couldn’t or didn’t.
Depending on the microbes involved, the end result of digestion may be a little or a lot of waste gas, explains Dr. Jared Leadbetter, one of the experts involved in the termite gut microbe study. Termites are great at digestion, while cows aren’t as efficient. This is because termites have large populations of bacteria called acetogens (a-see-toe-jens). Cows, on the other hand, have large populations of bacteria called methanogens (meth-an-oh-jens).
When a termite munches a meal of wood, its stomach enzymes break the wood bits into smaller particles. Then protozoa living in the insect’s guts break these bits down further into the basic elements hydrogen, carbon dioxide and acetate. The acetogens in the intestines then chow down, turning the hydrogen and carbon dioxide into acetate, which is an excellent source of energy for the microbes and the termite.
Basically the same processes are happening in cow stomachs and intestines except that the methanogens turn the digested food particles into methane gas rather than acetate. Since methane isn’t such a good souce of energy for the cow, it’s passed out of the body as waste gas. And the way it leaves is what we so eloquently call belches or farts. The majority of the methane is made in a cow's stomachs, or rumen, and is belched out. Some of the methane is made in the cow's intestines and is farted out.
Many animals, including two out of every three humans, have larger populations of acetogens than methanogens in their guts. So only about a third of people pass a significant amount of methane gas.
Most animals, birds, fish and insects pass gas. The average person passes gas about 10 to 15 times a day (some just do it more quietly than others).
One side note: methane is an odorless gas. The odors that sometimes result when people or animals belch or fart are caused by other compounds made during the digestion process. So don't blame the methane.
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