A U.S. diet expert has revealed what most of us always suspected - that airline food in economy isn't that healthy.

But meals on some carriers are better for us than others.

Dr Charles Platkin, a lecturer at the City University of New York School of Public Health, has revealed which domestic U.S. and Canadian airlines have made an effort to look after travellers' waistlines in 2015 - and named and shamed those that haven't.

He analysed and rated economy meals served on 12 airlines - and it was Virgin America that came out on top with 4.5 stars out of five. Dr Platkin, who also edits dietdetective.com, said the carrier was doing 'a fantastic job of creating healthy food'.

The worst rated were Frontier Air, Spirit Airlines and Hawaiian, which serves one meal with more calories than two Big Macs that would take 273 minutes of walking to burn off.

Points were deducted from the airlines if they weren't forthcoming with nutritional information about their meals.

Hawaiian said that it would cost US$17,000 to provide Dr Platkin with nutritional information for all the food it served, a claim he slammed as 'ridiculous'.

JetBlue and Delta were tied in second place with four stars, while Air Canada and United Airlines both scored 3.25 stars.

American was given 2.75, Alaska Air 2.5, Southwest Airlines 1.5, Allegiant Air 1.5, Spirit Airlines 1.25, Hawaiian 1.25 and Frontier Air just one point.

Virgin America, Dr Platkin said, was 'the clear leader when it comes to healthier foods' but said that it, along with all the other airlines, could put more effort into providing healthy snacks.

The average calorie count for Virgin's food, which includes meals, snack boxes and individual snacks, is 352.27.

The overall count for Hawaiian Airline's food, in contrast, is 588, with one meal, served on Hawaii to New York services, coming in at 1,266 calories. It contains turkey meatballs, steamed rice and cheese and crackers, plus a sweet treat.

Eating two Big Macs would pile on fewer calories as they have 550 each.

Dr Platkin is so unimpressed with Frontier Airlines and Hawaiian that he recommends passengers bring their own food. Frontier, he claims, doesn't offer anything healthy - just snacks.

He also reprimands the airline's PR team for being 'radio silent' on nutritional information.