Now that's what you call constipation. In other words, whether or not you're constipated depends on how often you normally move your bowels. True, 83 percent of Americans go at least once a day, according to one survey. But that doesn't mean the remaining 17 percent are constipated.

"There's nothing sacred about the daily bowel movement;" according to pharmacists Joe Graedon and Teresa Graedon, Ph.D., coauthors of The People's Pharmacy books. "Everyone is different. Anything in the range of three a day to three a week is perfectly normal."

Everyone has an occasional bout of "irregularity." But for some four million unlucky Americans, constipation is a chronic problem.

Most cases of constipation result from a combination of too little exercise, too little dietary fiber, and not enough fluids, says Anne Simons, M.D. Exercise stimulates peristalsis, the natural wavelike contractions in the lower colon that give you the urge to void. Fiber adds bulk to stool, which also prompts peristalsis. And fluids keep stool soft, so it passes comfortably.

Other factors can also raise your risk of constipation, says Alan P. Brauer, M.D. Just getting older makes you more prone to irregularity. Roughly 10 percent of American adults over age 60 have chronic constipation, compared with only 4 percent of younger adults.

Why the higher rate of constipation among older folks? One reason is that peristalsis naturally loses some of its oomph over time, Dr. Simons explains.

Another reason is that the body's production of stomach acid and pancreatic enzymes slows down. This makes for less efficient digestion and waste elimination, says Joseph Pizzorno Jr., N.D.

Besides age, certain medical conditions can contribute to constipation as can certain medications and iron supplements. Travel is another common culprit because it alters your eating and exercise habits as well as your bathroom "routine." If you're a woman, pregnancy can make you more prone to constipation, as your expanding uterus puts pressure on your colon and decreases peristalsis.

Of course, if you're like most people, you're probably less concerned about what has made you constipated than about how to get things moving again.