Airline food is improving, with one of the world's largest carriers making huge strides toward more healthful offerings, says Charles Platkin, an expert at the City University of New York School of Public Health who has been analyzing airline food for nearly 15 years.

He found the biggest improvement at Delta Air Lines, which jumped from eighth out of 12 airlines in 2013 to first place this year, tied with Virgin America.

Low-cost airlines such as Allegiant, Frontier, and Spirit ranked at the bottom.