A photo of a pepperoni pizza appears under the heading "What is junk food" on wisegeek.com, and sharecare.com runs the headline "Worst Junk Food #1: Pizza". The British newspaper The Mirror, in November 2013, told the story of a girl "addicted to junk food" who ate nothing but cheeseburgers, chips and… pizza.

The definition of junk food

There is no official government list of junk food, but it can be broadly defined — according to Andrew F. Smith's Encyclopedia of Junk Food and Fast Food — as any food preparation with an unbalanced content of saturated or trans fats, sugar or refined carbohydrates, flavourings and colourings. No vitamins, no fibre, no minerals.

The term was coined by Michael F. Jacobson, founder of the Center for Science in the Public Interest, who wrote in 1972: "Soft drinks are the quintessential junk food, all sugar and calories with no nutrients whatsoever. Americans are drowning in soft drinks." There is one worrying statistic: the consumption of food products rich in empty calories (high in calories and very low in nutrients), devoid of active compounds and full of colourings and chemicals, is growing visibly year on year, and there remains a great deal of misinformation on the subject.

Read also: The value of pizza, Unesco world heritage

In the Anglo-American world it appears to be widely accepted that pizza falls squarely into the category of junk food

Reading the ingredients of the new pizzas introduced this winter by Pizza Hut Canada, it is not hard to understand why. They have launched a beef poutine pizza — topped with chips, cheese and red meat — a bacon pizza with maple syrup, and a chicken pizza with cream cheese. Pizza Hut in China offers a pizza topped with hot dogs, prawn tempura and mayonnaise.

Frozen pizzas are indeed often made with industrial flour, obtained by industrially milling the wheat grain after removing the germ (the kernel's core) and the bran (the outer layer, rich in fibre), which impoverishes the raw material. Refined flour is extremely high in sugars and severely depleted of nutrients, but has the advantage of a long shelf life. The consumption of industrial flour is associated with a rise in blood sugar levels, an increase in insulin and, over time, the accumulation of stored fat.

The healthy pizza of Mike Lean, University of Glasgow

Some observers, more cautiously, note that certain dishes such as burgers, pizza and tacos can be considered either healthy or harmful depending on their ingredients, preparation and packaging.

In 2013, a research team was commissioned in Scotland by the company Eat Balanced to devise a new set of ingredients for a perfectly balanced pizza. The team, led by nutritionist Mike Lean of the University of Glasgow, together with Emilie Combet, Amandine Jarlot and Kofi Aidoo of Glasgow Caledonian University, noted that, in its traditional recipe, pizza "should be a meal that is low in fat, provides a good portion of vegetables and contains ingredients associated with better cardiovascular health". In practice, for commercial reasons, most pizzas "have more salt and fat than is desirable and are lacking in essential vitamins and minerals". The research concluded with the creation of a new pizza recipe that contains 30 per cent of all required daily nutritional elements — in other words, a perfect meal: made with wholemeal flour, little salt, the addition of Scottish seaweed in the topping to provide vitamin B12, iodine and fibre, and chilli pepper for an extra pinch of vitamin C.

The perfect pizza for health is our own

Apart from the seaweed, these appear to be precisely the ingredients of an authentic, beloved, time-honoured Italian pizza.

Its health secrets lie in the well-leavened dough, which reduces the need for salt; the generous ladle of tomato sauce, rich in lycopene; the sprinkling of fior di latte or buffalo mozzarella, whose fats enhance the absorption of antioxidants; the raw extra virgin olive oil, full of monounsaturated fatty acids, polyphenols and vitamin E; aromatic herbs; and chilli pepper.

Read also: The history of pizza, from the Neolithic to Unesco recognition

This is why a study published in 2004 in the European Journal of Clinical Nutrition showed that eating pizza more than twice a week reduces the risk of a heart attack to less than half. According to another study published in the International Journal of Cancer, Italy's emblematic dish reduces the likelihood of cancer of the digestive tract, thanks to its tomato-based topping. Junk food does not have these effects.