Questions about gas and food can be awkward. So I called the experts — gastroenterologists — for answers.

Q. What makes a food gassy?

A. Foods that contain carbohydrates can cause gas. Fiber, in particular, is a culprit, because it's not easily digested — especially when first introduced into your diet. Basically, undigested sugars pass into the colon unabsorbed, leading to gas. By contrast, fats and proteins cause little gas.

However, according to Dr. Philip Jaffe, an associate professor of medicine at the University of Connecticut Health Center, "Any food that contains material which doesn't get broken down and absorbed in the small intestine can cause increased gas production."

Some people have difficulty digesting certain foods. Partially digested food passes from the small intestine to the large intestine (colon). There, bacteria digest the food, leading to the production of gas (nitrogen, hydrogen, methane, carbon dioxide and others). In fact, humans aren't well-equipped to break down many plants; we don't have the enzymes for doing that.

Q. Why do our bodies pass gas?

A. Flatulence protects our bowels from becoming distended, which could cause us to blow up like a blimp. We become bloated when gas gets stuck behind a bowel obstruction, says Dr. Michael Levitt, a spokesman for the American Gastroenterological Association.

Q. How and why do we burp?

A. According to Jaffe, "Burping is triggered by distention (bloating or swelling) of the upper part of the stomach, leading to the regurgitation of gas from the stomach through the esophagus and then out through the mouth." He adds that it is an involuntary reflex, but once sensed, it can be controlled by not relaxing the upper esophageal sphincter valve and re-swallowing the air.

Q. Is it normal to feel gassy all the time?

A. "Most people — including women — pass flatus 10 to 20 times daily, between a pint and four pints a day," says Jaffe.

Passing a lot of gas is nearly always normal but could also signal a malabsorption problem from certain foods. Feeling bloated after eating is usually normal as well, but may sometimes be an indication for disease.

Q. What about gas pains?

A. Most experts agree that eating too much fatty food can cause bloating and gas pains, mainly because the fat in your system slows down stomach emptying and, as a result, gas builds up. In terms of danger, a rule of thumb is that gas pains that are relieved by belching or flatulence probably aren't dangerous, says Jaffe.

Q. Why does gas smell?

A. The odor comes from bacteria in the large intestine, which produce small amounts of foul-smelling sulfur gases, says Dr. Patricia Raymond, a fellow of the American College of Gastroenterology. "Foods such as meat, eggs and fish stimulate colonic bacteria to produce sulfur-containing gases," says Jaffe.

Smelly belches are more likely "old food" in the stomach, which, Jaffe says, is typically a result of a problem with gastric emptying or a blockage of the gastric outlet. Conditions that could lead to this include diabetes mellitus and cancer.

Q. Are there other causes of excess gas besides food?

A. Food is the major cause, others include: