There was a touch of schadenfreude last week when it was reported that even in Italy, Greece and Spain, the home of the Mediterranean diet, children are suffering the same obesity crisis as here in the UK. They thought they were so clever with their olive oil and fish and fresh vegetables. They were laughing at us Brits with our chips and burgers and, er, more chips. But look! Fast food has got them too! No one escapes Ronald McDonald. The march of obesity has felled even the great Italian matriarch wielding her wooden spoon dripping with homemade tomato sauce.

According to the World Health Organization, Greece, Spain and Italy have rates of childhood obesity well over 40%. Dr João Breda, head of the WHO European office for prevention and control of noncommunicable diseases, pronounced the Mediterranean diet dead, face down in a plate of spaghetti.

The global food system, which has made commodities such as beef and corn syrup so cheap and plentiful, was blamed. Television stations showed children waddling out of the same McDonald’s, Burger King and KFC we have in Britain in the centre of Rome, Madrid and Athens. How could the kids stand a chance surrounded by such temptation and powerful marketing forces using their favourite cartoon characters?

A McDonald’s sign near St Peter’s Basilica in Rome. Photograph: Tiziana Fabi/AFP/Getty Images

At the same time, reporters interviewed parents about their busy lifestyles. How was it possible for any modern family, struggling to make ends meet, to cook from scratch every evening? It became clear that the good people of the Mediterranean, instead of growing vegetables and gathering around the table for salad and sardines every evening, were flopping down in front of the telly to eat a takeaway – just like us.

But is this really such a surprise? That in 2018, families all over Europe are struggling against a food system stacked against them?

Let us examine the Mediterranean “diet” more closely. For outsiders’ consumption, it developed in the 1960s, based on the eating habits of Greece, southern Italy and Spain. The diet is characterised by lots of fruit, vegetables and fish, use of olive oil and moderate consumption of dairy, red meat and simple sugars. It took off in the 1990s when studies found that it could lower the risk of cancer and heart disease.

It seemed like a miracle cure and, like most fad diets, led to a number of recipe books. What most of the books failed to mention is that the studies also made clear that the Mediterranean diet had to be accompanied by other factors.

The most obvious is exercise. Children in Spain, Italy and Greece are spending more time in front of their screens. Even if they are eating a Mediterranean diet, they are not burning it off.

Less obvious factors in the success of the diet are psychological.

In his book The Blue Zones, about the places on Earth where people live the longest, Dan Buettner visits Ikaria in Greece, where there is the highest percentage of 90-year-olds on the planet. He attributes the longevity to a Mediterranean diet, but also the “mountain way of life”, to fostering family and social connections, to growing your own fruit and vegetables, to napping and laughing and basically enjoying life.

A village feast – with dancing – on Ikaria, the Greek island with the most nongenerians in the world. Photograph: Alamy

It is tempting, given the latest statistics on childhood obesity in Spain, Italy and Greece, to conclude that the Mediterranean diet has failed. Already, there are suggestions that we should be adopting a “Scandi diet” rich in omega-3s and whole grains, given that in Denmark under 10% of children are obese. As I write, conscientious parents are training their children to enjoy herring and rye bread for breakfast.

But would it really solve the problem? After all, it is only a diet. And diets don’t work. They just make people feel guilty and bring out unpleasant emotions, like schadenfreude.

What does work are habits passed down from a grandmother and supported by a whole food culture. Even the British diet could be seen as healthy if you do it right – shock horror! If you eat a little butter and red meat, restrict sugar and cook plenty of home-grown vegetables, just as we did during rationing in the Second World War, then you won’t be obese.

The fact is that most national diets are healthy because they have evolved as the best way to use the locally grown food. But they need to be accompanied by a retail sector that makes this food accessible and a lifestyle as stress-free as possible. I am sure there are plenty of grandmothers in Italy still living to 100 because the village presses its own olive oil, but most of the young people have gone to the cities to work.

In Greece, families are relying on food banks to survive. In southern Spain, they grow plenty of fresh fruit and vegetables, but mostly in polytunnels for export to northern Europe. Access to fresh fruit and vegetables for most people in the Mediterranean, just as in the UK, is restricted to what is available and cheap in the supermarkets.

To solve childhood obesity will take more than fads – it will take the transformation of the whole food system. It will mean controls on advertising junk food to children and money for schools to promote exercise. It will take educating children not just to cook food but to grow food. It will mean a system of agriculture that rewards farmers for growing healthy food. It will mean creating local networks so that families can access seasonal and fresh food. It will mean examining our work culture to find time to exercise and to cook. And it will mean remembering how to eat together as families and friends.

To give children a long and healthy life, we need to teach them about more than a diet – we need to teach them how to shop, how to cook and how to live.