Q. Is there such a thing as “traveler’s constipation”?

A. Traveler’s constipation is probably real. And the scientific evidence behind it is fascinating.

The largest study of traveler’s constipation appeared 40 years ago in the Swiss medical journal Schweizerische Medizinische Wochenschrift. The authors administered a questionnaire to 10,500 tourists returning to Switzerland after visiting the tropics. They found that 14 percent of the respondents experienced constipation associated with air travel.

Thirty years later, these findings were supported by a small study of missionaries returning to the United States from overseas. Of 68 subjects who responded to a questionnaire, 9 percent reported travel-related constipation.

But the most robust study — one that is probably unique in the annals of medicine — appeared in 2003 as a modest letter to the editor in the American Journal of Gastroenterology. Spanish gastroenterologists studied 70 people traveling from Europe to the United States for a short stay. In addition to the usual questionnaires, all subjects maintained diaries on their bowel habits, had stool samples evaluated for consistency according to a standardized methodology, and had their colonic transit time measured after ingesting radioactive tracers. Colonic transit time is the time required for stool to move through the large intestine.