Airline food is notoriously bad, and it's also notoriously bad for you. But which airline has the worst food? And if you have no choice but to eat bad food in the air, where can you at least find the best options?

Charles Platkin Ph.D, otherwise known as the Diet Detective, surveys the nutrition on in-flight food each year, and his most recent study shows the best and the worst of 2013. If you're one of the 5.5 million people traveling by air this holiday season, you may want to pay close attention to the Diet Detective's findings.

The best airlines for nutrition are Virgin America and Air Canada. On Virgin America, the average calories per meal or snack box is 360.75, and the average calorie count for an individual snack is 270.63. The airline also offers a Travel Light menu, something unique in the industry. If you think that a roasted pear and arugula salad with almonds and a fig mustard dressing sounds like something you might eat when you arrive at your destination, think again. It's on Virgin America's Travel Light menu.

Air Canada's meals and snack boxes average 296.90 calories each, and the individual snacks 365 calories. Platkin notes that the airline introduced Twizzlers and candies this year, but overall, it still ranks as one of the best for nutritional options. Passengers can choose from celery and carrots with ranch dip, and hummus with pretzels. One of their lowest calorie meals is a shepherd's pie, coming in at 390 calories.

Frontier, Southwest and Allegiant airlines serve the worst food. Frontier doesn't serve meals -- only snack boxes and individual snacks -- and its snack boxes weigh in at an average of 613.67 calories per box. The airline does not offer fresh food options, and while it slightly redeems itself by offering Larabars and Kashi oatmeal, most of the snacks consist of candy or chips.

Southwest only offers a minimal selection of individual snacks, which are all fairly unhealthy. On most flights passengers have the thrilling choice of honey or dry-roasted peanuts or pretzels, and select flights offer Nabisco Airplane Cookies (yum?), Ritz crackers and Wheat Thins.

Allegiant was apparently uncooperative and did not provide any nutritional information to Platkin. The average calorie count for meals and snack boxes was 500.40, and 366.36 for individual snacks. Platkin suggests nuts and beef jerky are the healthiest snack choices, and a turkey sandwich without cheese the best option for a meal.

Despite somewhat depressing findings, airlines are moving in the right direction, albeit slowly. The average number of calories dropped from 388 per item to 360. Still, as Platkin points out, the healthy food market is booming, and the airline industry isn't really keeping pace. Americans are making healthier choices than they did 10 years ago. Now the airlines just need to catch up to the trend.

For full results, head to DietDetective.com.