They're all at it. This week Burger King was criticised by the Advertising Standards Authority for giving viewers a false impression of its premier brand, the Whopper. Instead of the large version praised by burly men singing a "manthem" in one of the company's television commericials, the store was serving far smaller burgers.

In the spirit of investigative inquiry, The Independent launched its own survey of fast-food classics as portrayed on advertising billboards and compared them with the real thing. The contrast, to say the least, was stark.

The Independent ordered a Big Mac from McDonald's, a Double Whopper from Burger King, a Cheesy Bites pizza from Pizza Hut and a Bargain Bucket from KFC. Our conclusions are presented alongside. In the meantime it is worth pointing out that even if the hype is seductive these are dishes that could seriously extend your waistline.

All the companies stress that their food is suitable for the whole family, but all four were loaded with salt and sugar, and two had more than the total recommended amount of calories, salt and fat for a whole day. Even on a subjective level, the food was greasier and less wholesome than it appeared in advertisements.

Analysis of the companies' websites showed the food was stuffed with artificial ingredients; a Whopper bun alone has six potentially harmful e-numbers. A Double Whopper with cheese contained 923 calories - almost half of the daily limit of 2,000 recommended by nutritionists for a woman. Combined with small fries and Coca-Cola, the calories soared to 1,413. The Pizza Hut pizza contained an astonishing 2,560 calories - 60 more than the recommended daily intake for a man, while each KFC nugget contained 258 calories.

Peter York, the brand consultant, said that the firms sought to connect with youth culture through music, fashion, visual effects and "insider symbolism," using "visual shorthand for 'our culture'."

The British Dietetic Association advised people to limit their consumption of fast food and to top up such meals with fruit. One problem, Dr Frankie Phillips said, was that salt was automatically added to fries.

McDonald's Big Mac

McDonald's premier brand came in a box blazoned with the legend "I'm lovin' it!", translated into French and German and two oriental languages. The cheese in The Independent's burger was a peculiarly disgusting orange hue. Perhaps not surprising, given that Which? identified ingredients like trisodium citrate, diphosphates, polyphosphates and sorbic acid in it. The burger had measly slivers of lettuce and a gherkin so pale it may have been anaemic.

KFC Bargain Bucket

The starkest contrast between reality and advertising lurked in the KFC bucket - a large cardboard container half-filled with chicken pieces. Coated in breadcrumbs, the chicken was as unappetising as an appointment for root canal work, only without the knowledge that it would do you good. The six pieces totalled 1,548 calories. By the third, the safe daily limit for salt (each piece has 2.5grams) had been exceeded. A dismal, soulless example of industrial techno-food .

Burger King Double Whopper

Weighing in at 923 calories, our Whopper looked little like the carefully arranged versions held by burly men in the TV adverts. Comprising a sesame-seed bun and two large patties, it was slathered in high-calorie mayonnaise. There was a cursory nod towards health: a few slivers of bedraggled lettuce and a slice of tomato. A microscope was needed to spot the onion. The wrapper was covered in greasy fingerprints.

Pizza Hut Cheesy Bites Pizza

In adverts for the pizza chain, a slice is gently lifted to reveal melting cheese and choreographed toppings. The red onion and the tomatoes face upwards in an appealing manner. In reality, this fatty pizza had a random sprinkling of tomato, green pepper and red onion and vastly larger quantities of white flour and gloopy, tasteless cheese. Where there should have been mozzarella, there was industrial cheese. Where there should have been fresh vegetables, there were limp examples.