You may have drooled over all those advertisements from many airlines that tout how tantalising their in-flight meals are - but are these promises just a flight of imagination on the airlines' part?

A new book, Gastrophysics: The New Science Of Eating, has come out to back what many travellers have come to believe and tolerate - airline food is just edible, but is nothing much to write home about on a postcard supplied by the airline.

But they may not have known that the underwhelming in-flight meals are also a health risk as they have more calories.

"The lower cabin air pressure, dry cabin air and the loud engine noise all contribute to our inability to taste and smell food and drink," the book's author, Professor Charles Spence, a lecturer at Oxford University, told the Business Insider.

"Because sound suppresses sweetness perception, you have to add about 15 to 20 per cent more sugar to the foods we eat while in the air to give the same taste perception."

According to Prof Spence, there are other factors to explain why passengers could end up at the destination airport heavier than when they first board the plane.

"There is the boredom," he told the Daily Telegraph in another interview. "With nothing else to do, food becomes an appealing distraction. And when it is being offered for free, it will be even harder to resist."

Many plane passengers would surely have noticed other people on board badgering the stewardess for second helpings, from bread to desserts, and regular servings of both alcoholic drinks and fruit juices.

This is despite knowing that the air in an aircraft is very dry and, coupled with the diuretic effect of drinking alcohol, they may become dehydrated much faster than on the ground.

The amount of eating and drinking is also driven by the in-flight entertainment. "Another really big problem is the movie or television show you watch," said Prof Spence. "It is not uncommon to find people eating as much as a third more food with the TV show on."

The figures, at least for British travellers, are not likely to put anyone on cloud nine,

Prof Spence's book cites research which suggests that the average Briton consumes nearly twice the recommended daily intake of calories while heading to their destinations.

"It has been estimated," he wrote, "that the British consume more than 3,400 calories between their check-in at the airport and their arrival at their destination."

But while some airlines try to offer healthier options, the relentless dogfight for business - amid rivalry with budget airlines and pressure to keep ticket costs competitive - means that many players cannot afford to fly the extra mile for nutritional value.

"More often than not, though, the airlines have opted to load the food they serve with even more sugar and salt, to enhance the flavour," Prof Spence told the Daily Telegraph.

"No surprise, therefore, that the food served these days isn't the healthiest."

Travel experts have noticed another ploy adopted by airlines - roping in celebrity chefs to give their menus a touch of glamour. Prof Spence is not impressed, however.

"I have yet to see any evidence to support the claim that the chef's interventions... actually led to a significant increase in passenger satisfaction," he wrote.

On this, he is backed by noted chef Gordon Ramsay who rarely minces his words.

"There's no f***ing way I eat on planes.

"I worked for airlines for 10 years, so I know where this food's been and where it goes, and how long it took before it got on board," he told the Refinery29 website recently.

Most meals are made between 12 and 72 hours ahead of the time that they are dished out on the plane.

Professor Peter Jones, former professor of travel catering from Surrey University, told the Daily Mail: "It can be kept in a chilled stage for five days under the internationally recognised food hygiene standards."

Ramsay's method to beat the inflight food blues? Going for a snack at an Italian bar in the airport before his flight.

Meanwhile, disgruntled plane passengers are fighting back. They have documented shocking examples of in-flight food, complete with photographs.

Postings in a website called Airlinemeals.net have gone viral with the hundreds of images which show what is served at more than 9,000m.

But all is not lost, at least for those who fly on Asian airlines.

Indeed, the site's anonymous founder and webmaster, a 35- year-old graphic designer from Holland, praises Asian airlines for their menus.

"I would say airlines from Asia get the best results... Singapore Airlines, Japan Airlines, Cathay Pacific, Thai Airways International, Emirates... and from my own experiences, I would like to add Qatar Airways and Vietnam Airlines," he said. "'They're all top notch."

•Gastrophysics: The New Science Of Eating (US$15.69 or S$21.70) is available for pre-order at Amazon.com.