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What a gas!: Michael Jordan does it. So does Britney Spears. Everyone passes gas--on average 14 times a day! While the phenomenon (called flatulence) is often the butt of jokes, "farting" is as natural as taking a breath. (Teen health issue: digestive system * microbes).

"In fact, a lot of the air people pass from their behinds is from the air they swallow," says gastroenterologist (stomach and intestine doctor) Judy Sondheimer of the Denver Children's Hospital. You gulp in air when you eat too fast, swallow fizzy drinks, chew gum, or even talk a lot. And while most swallowed air is belched out the mouth, a small amount passes through your body to "pop" out the rear end. The other cause of gas? Freeloading microbes (tiny organisms, like bacteria) that thrive and feed inside your colon (large intestine).


A noisy toot starts at the top of your digestive system --the system that breaks down food into simple nutrients so you can absorb them for energy (see diagram, far right). Just the thought of a burger whets your mouth with saliva. It enters the mouth as huge molecules of proteins, fats, and carbohydrates--substances your body needs for healthy growth and energy. Biting and chewing breaks food down into smaller pieces. At the same time, salivary digestive enzymes, chemicals that turn larger molecules into smaller ones, go to work. Carbohydrates (like a burger bun) begin breaking into simple sugars.

Every swallow sends partially digested food into your stomach. There, the glob gets mixed and churned with juices containing more enzymes and hydrochloric acid (acid that digests protein and kills bacteria). Proteins, made of long chains of amino acids, start to break into individual acids. Up to four hours later, chyme--the now mushy soup of food--passes into the small intestine. Even more digestive enzymes continue to break down carbohydrates and proteins. And fat turns into tiny droplets. At this point, all digested nutrients are absorbed, or transported, to the bloodstream to fuel cells.

But your body doesn't contain the enzymes to digest everything you eat, including oligosaccharides--a group of sugars found in some plant fibers, like beans for example. And some people can't digest a complex sugar called lactose, found in dairy products. Undigested food travels to the colon.


More than 5,000 species of microbes hang out in the colon. It's an ideal environment for microbial growth: the colon is warm, moist, and free of bacteria-killing acids found in the stomach and small intestines. Plus, there's your leftovers!

These microbes possess the enzymes to break down the foods your body's enzymes can't digest. The bacteria metabolize food (convert nutrients into energy) and use it to build new cell structures. But in the process of metabolizing, the microbes give off gaseous waste that produces your toots. (You also produce gas when body cells metabolize nutrients, but this gas escapes the body via the lungs at exhale.)

Some of the bacteria's gases--nitrogen, oxygen, carbon dioxide, hydrogen, and methane--are the same gases that make up the air you breathe. They also compose 99 percent of the atmosphere in the large intestine. So what gases cause the stinker? Researchers aren't sure which of the 200 trace gases in the remaining 1 percent is the culprit. The prime suspect: "It's probably hydrogen sulfide," Sondheimer says. The gas usually smells like rotten eggs.

Any way to avoid flatulence? Forget it. Most foods contain some indigestible fiber, and fiber is an essential part of a healthy diet, helping to prevent heart disease and certain cancers. But, for the exceptionally gassy there are enzyme supplements (like Beano, or Lactaid for the lactose-intolerant) that help digest food before it reaches the colon. And if your flatulence is unusually severe, it may be an indicator of other health factors. Time to visit a doctor.


Follow food on a 24-hour, 9.5-meter (31-foot) journey through your digestive system.

1. Mouth

Salivary glands pump out 1.2 liters (5 cups) of saliva every day. While chewing breaks food into pieces, enzymes in saliva break down food chemically.

2. Esophagus

Powerful muscle contractions called peristalsis move food down this tube toward the stomach, then through the stomach and intestines.

3. Stomach

Digestive glands pour out gastric (stomach) juices of enzymes and hydrochloric acid to begin protein digestion. Food churns for up to four hours, turning into mush. Then the stomach forces food bit by bit into the small intestine.

4. Small Intestine

Digestive enzymes and fluids further digest food particles. Here, the simple molecules of nutrients--amino acids from proteins, glucose from carbohydrates, and fatty acids from fat--pass through the walls into the bloodstream to fuel cells.

5. Large Intestine

Indigestible food passes here. The leftovers feed 5,000 species of bacteria that metabolize food--a byproduct is flatulence. Here, water is also absorbed into the blood, solidifying waste material.

6. The End

Solid waste (feces) sits in the rectum waiting to be expelled. It's half bacteria by weight, contains hard indigestible food and remains of digestive juices, mucus, water, air, and dead cells from the gut wall.


Lesson Plans


Did You Know?

* The medical term for flatulence is "flatus," which in Latin means blowing.

* Peristalsis moves gas toward the anus. As gas expels, the vibrations of the anal opening--based on velocity of gas expulsion and tightness of the sphincter muscles--determine the sound quality of flatulence.

* The temperature of flatulence is approximately 37 [degrees] C (98.6 [degrees] F)--your body's temperature.

Cross-Curricular Connection

Social Studies: Create and design an advertisement for an original gas-relieving product.

National Science Education Standards

Grades 5-8: personal health * regulation and behavior * structure and function in living systems * populations and ecosystems

Grades 9-12: the sell * the interdependence of Organisms * matter, energy, and organization in living Systems * personal and community health


For more on flatulence: 9339/9999.html

For a review of how the digestive system works: diges.htm

Directions: Answer the following in complete sentences.

1. Explain two flatulence-producing processes.

-- 2. Describe two methods to lower the amount of flatulence.


What a Gas!

1. Process a: Swallowing air may cause flatulence--while most is belched out of the mouth, a small amount passes through the body and "pops" out the other end. Process b: Colon-dwelling microbes possess the enzymes to break down food you can't digest. The byproduct is gaseous waste.

2. Eat slowly and cut down on fizzy drinks mad chewing gum. You can't eliminate flatulence because most foods contain some indigestible fiber. And fiber is an essential part of a healthy diet, helping to prevent heart disease and certain cancers. But for the uncomfortably gassy, there are enzyme supplements that can help digest food before it reaches the colon.
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Publication:Science World
Geographic Code:1USA
Date:Dec 10, 2001
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