Picture the first day of college: unpacking extra-long twin sheets, unloading the mini fridge, meeting the roommate and pinning up that Bob Marley poster. 

For many students, that classic college introduction doesn't happen. Nearly one in five freshmen, on average, commuted or lived off campus in fall 2015, according to data reported by 245 ranked National Universities. 

One tempting reason to forego the traditional dormitory experience is cost. At the 1,109 ranked colleges responding to an annual survey, room and board ran an average $9,999 in 2014-2015. Students who live at home may be able to save a sizable chunk of change. 

One of those students was Katie Thompson, who bunked with family members – first at her aunt's house and then with her mother – while attending two community colleges. She later transferred to Virginia's George Mason University, where she also lived off-campus while earning her bachelor's degree. While she wonders how a more traditional residential college experience would have shaped her career path, she can't argue with the cost savings. 

"As far as the money, I'm definitely a success story," says Thompson, who repaid her $5,500 debt in two years. 

But experts warn that living off campus can cause students to miss an integral part of the college experience, especially at residential institutions. 

"There's an awful lot of worry we have when a student commutes from home," says Tom Delahunt, vice president for admission and student financial planning at Drake University, a private residential campus in Iowa. 

Here's what to think about before making the choice to live at home during college. 

• Consider the school: Living at home can be a no-brainer for those attending one of the many colleges catering to commuters. Students taking online courses may rarely need to travel to the institution, much less move into the dorms. At those schools, living at home is par for the course. 

On the flip side, living in the dormitories is a key part of the experience at some traditional four-year colleges, where commuters are a minority. 

"Student experiences really depend on the culture of the school," says Samantha Elliott, associate professor of biology at St. Mary's College of Maryland, who's taken note of how commuters perform in her class. 

She's found that those students tend to struggle finding study buddies on St. Mary's residential campus. "Because they're not on campus at those late evening times when most students end up scheduling study groups, we've really had to make efforts to encourage and help students make those connections," she says. 

• Tally the costs of commuting: When it comes to the cash benefit of living at home, "let's make sure it's money saved and not money not-spent," says Delahunt. 

He cautions students against overspending on a car, gas, insurance, parking and other costs associated with commuting. 

Another drawback, especially at a residential college, is that living at home may cut aid. One big risk is that students will assume that living off-campus is always cheaper than lodging on-campus, says Scott Juedes, director of student financial services and financial aid at Wellesley College in Massachusetts. 

He points out that institutional need-based grants at Wellesley may be available to cover on-campus living costs but not expenses accrued while living at home or off-campus. 

• Contemplate the experience: Many traditional four-year colleges have a strong foundation in campus culture. And experts worry that missing out can be detrimental to a student's academic and social success. 

Feeling connected and engaged in a college setting can help guide students toward an on-time graduation, say experts. "The students that do commute are a bit of a retention risk for colleges," says Delahunt. 

Graduating late – or dropping out entirely – can cost students in delayed earnings and extra tuition payments. 

Delahunt recommends landing an on-campus job as a way to earn money and engage in the college community. 

Commuters who do well, especially when they're not the norm, tend to be extroverts when reaching out to peers, mentors and advisers during their more limited on-campus time. "Don't be afraid to ask for help and ask questions," says Elliott, of St. Mary's. "It doesn't mean you have to stand up in front of a class of people."

There's no doubt about it: Americans are getting heavier and heavier. But new U.S. estimates may still come as a shock -- since the late 1980s and early 1990s, the average American has put on 15 or more additional pounds without getting any taller.

Even 11-year-old kids aren't immune from this weight plague, the study found. Girls are more than seven pounds heavier even though their height is the same. Boys gained an inch in height, but also packed on an additional 13.5 pounds compared to two decades ago.

When looked at by race, blacks gained the most on average. Black women added 22 pounds despite staying the same average height. Black men grew about one-fifth of an inch, but added 18 pounds, the study found.

"We are not doing nearly enough to control and reverse the obesity epidemic and doing far too much to propagate it. This is another notice of that sad fact," said Dr. David Katz. He directs the Yale University Prevention Research Center and is president of the American College of Lifestyle Medicine.

The new statistics were released Aug. 3 in a report from the U.S. Centers for Disease Control and Prevention's National Center for Health Statistics. The statistics for 2011-2014 are based on an analysis of a sample of 19,151 people who underwent medical examinations and were interviewed at home.

According to the report, the average weight of men in the United States rose from 181 pounds to 196 pounds between 1988-1994 and 2011-2014. Their average height remained the same at about 5 feet, 9 inches.

The average woman, meanwhile, expanded from 152 pounds to 169 pounds while her height remained steady at just under 5 feet, 4 inches.

How big of a deal are these weight gains?

"A 15- to 16-pound weight gain is fairly significant and typically would be consistent with a couple of points increase in body mass index," said Anthony Comuzzie. He's an obesity researcher and scientist with the department of genetics at the Texas Biomedical Research Institute in San Antonio.

Body mass index, or BMI, is a rough estimate of a person's body fat using height and weight measurements. The BMI classifies people into several categories, such as normal, overweight and obese.

"From a practical point," Comuzzie said, the average weight gain "means that someone who was on the high end of normal weight would have likely moved into the overweight category, and those at the high end of the overweight category would have likely moved into the obese category."

This matters because "we know that increasing BMI is a good indicator of overall risk for a variety of diseases, including heart disease and diabetes," he said.

The reasons behind the increase in weight are complex, according to Comuzzie. In part, he suggested, it's related to trends toward less exercise and more access to food that's rich in calories.

But "at the end of the day, it is still fairly basic physics: If energy consumed is greater than energy expended, then there will be a gain in weight," he said.

Could the U.S. population be getting fatter because it's getting older overall, and developing lower metabolisms?

Both Comuzzie and Katz discounted this explanation since the new report matches age groups for the two time periods.

Comuzzie said the findings reveal that the U.S. population is still gaining weight at "a fairly rapid rate, and such an increase does not bode well for the overall health of the nation. The findings suggest there will likely be an associated increase in chronic diseases like type 2 diabetes and heart disease in the coming years," he noted.

As for next steps, Katz said there's much to be done. Whether that will happen is another matter.

"There are many active efforts to combat obesity, but our culture at large is in the business of propagating it for profit, from big food to big media to big pharma. It's that simple. We do much more, across the expanse of our culture, to foster obesity than to defend against it," Katz said.