Researchers of the University of Toronto analysed the offerings at 19 large chain fast-food restaurants. They found that the typical meal contained 56 percent of the daily 2,000 calorie recommendation for adults. Breakfast portions alone averaged out at 1,226 calories.

Commenting on the results, Mary Scourboutakos from the research group said that the calorie count wasn’t the only cause of concern. She pointed out that "on average, they contained 151 percent of recommended daily salt intake, 89 percent of daily fat, and 60 percent of daily cholesterol”.

However, another analysis carried out by Tufts University in Boston has shown that fast food restaurants are not even the worst offenders for those looking to eat out while minding their waist. The food offered by smaller chains and individual restaurants ended up with even higher calorie counts than their big chain equivalents, with a 1,327 calorie average per meal. The researchers suggested that increasingly large portion sizes were partially to blame for the counts, as well as well-known offenders like unhealthy sauces, dressings and toppings.

The Boston group looked at 33 different restaurants in their local area. Mexican, American, Chinese, Italian, Japanese, Thai, Indian, Greek and Vietnamese eateries were included. Inevitably some types of cuisine proved healthier than others. The average carb-heavy Italian meal proved highest with 1,755 calories – nearly double that of Vietnamese meals (922 calories).

Speaking to New York Daily News, Dr. Susan Roberts from Tufts University said "It's ridiculous that when my dieters say, 'Where is a place I can reliably eat?' I'm going to have to say fast food. If you're trying to lose weight and want a restaurant meal for less than 500 calories, go have a salad at McDonald's."

Perhaps the simplest advice of all, however, is to eat at home, where you'll be in control of the menu and portion sizes.