A week's vacation may leave many adults with a heavier midsection–extra weight that can hang around even six weeks post-vacation.A faculty member in the University of Georgia's College of Family and Consumer Sciences found that adults going on a one- to three-week vacation gained an average of nearly 1 pound during their trips. With the average American reportedly gaining 1-2 pounds a year, the study's findings suggest an alarming trend."If you're only gaining a pound or two a year and you gained three-quarters of that on a one- to three-week vacation, that's a pretty substantial weight gain during a short period of time," said Jamie Cooper, an associate professor in the college's department of foods and nutrition.