For most Americans, eating healthy day in and day out is a challenge.
According to a new study, that challenge becomes even more difficult on a plane.
Charles Stuart Platkin, founder of the Web site Diet Detective, recently reviewed the food offered by six major airlines.
"You want to set the tone for your trip, and what you eat could impact that," Platkin said.
A United Airlines' snack box, filled with potato chips, salami and a cookie, sets passengers back $5, 550 calories, and almost half a day's worth of sodium.
Still, United offers some of the airline industry's healthiest options.
Delta's snack basket, also $5, packs 766 calories in chips, peanut butter crackers, and other goodies.
A passenger would have to walk for 3½ hours to burn off this snack, and Platkin says the food doesn't even do its job.
"You're eating empty calories so things like crackers or candy bars, you're not going to feel fulfilled," he said.
Most airlines don't provide nutritional information about their snacks, which makes it difficult to make the right choice.
Good options are out there.
Jet Blue offers free individual bags of nuts and animal crackers. And United recently introduced a snack box called "rite bite," which features tuna, hummus and Gouda cheese.
"The key is responding [to] the needs of our customers. They're telling us clearly they want healthier options, and we're responding," said Dennis Cary, United's senior vice president of marketing.
ABC News called all of the major airlines for comment.
US Airways and American Airlines would not give out nutritional information on their snacks, even over the phone.
Delta, which had the most high-cal snack box, didn't return ABC News' calls.
So what's the best approach to eating in the air?
Bring food onto the flight. Here are some healthy, portable snack options:
Yogurt, if below the 3-ounce security maximum
Most importantly, bring water, which must be bought after the security check.
Dehydration can lead to jet lag, fatigue and hunger, which can make that unhealthy airline meal seem all the more appetizing.