The prandial is political

Today, I am celebrating a birthday - the first anniversary of the foundation of the Instituto Tomas Pascual, named after a Spanish philanthropist who started in life selling sandwiches from a barrow on railway platforms and who ended with an empire.

His dairy business was, by the time of his death a couple of years ago, the most sedulously modernised in Europe. Quality and purity were his obsessions, and he became a crusader for healthy eating - not just because it was good for his business, but because public health was a vocation that grew on him and took over his life.

Pascual's career coincided with the transformation of Spain from a poor country, economically isolated by a dictatorship that celebrated autarchy and defied the world, to a land of democratically induced Wirtschaftswunder. When he started, hunger menaced his fellow countrymen. By the time he died, obesity was the biggest food-related threat they faced.

His heirs founded the institute to honour his memory and to continue his work. Disinterestedly, it organises research and education on an impressive scale and at an intensive pace. Events happen weekly in Madrid. The Instituto's birthday party consists of an evening of lectures in the gloriously enlightened, gilded and plush-seated auditorium of Spain's Royal Academy of Medicine.

But I feel guilty about my own talk at the event. I'm notoriously free with jokes on the lecture platform, but this time I provoke more than laughter by pointing out some awkward, embarrassing features of health education. The public health campaigns of the past 40 years have failed. We have blasted and basted the public with dietary advice and they have responded by gorging on junk. We have extolled diet and exercise and in return we have got the fattest populations the world has ever seen and the highest levels ever of diabetes and food allergies.

By over-recommending carbohydrates, dietary professionals unwittingly aided the purveyors of the sugars and starches that have tickled appetites and expanded waistlines. By inventing meaningless forms of quantification - "pieces" of fruit, "units" of alcohol, "servings" of greens - they made their advice sound unscientific, arbitrary and unintelligent. By demonising lipids, they deflected purchasers from healthy polyunsaturates. Proprietary slimming diets and professional food faddists contradicted each other and - as often as not - disappointed their customers.

By excoriating fatness, health-industry personnel have colluded with fashionistas and encouraged anorectics. By conducting carpet-bombing campaigns against salt and sugar, they gave public health education a bad name. By untargeted condemnation of cholesterol, instead of controls focused on consumers who were genuinely at risk, they undermined public confidence in officially endorsed dietary advice. By taking a moralising attitude against alcohol - which, in moderation, and especially in the form of wine, is one of the healthiest and most civilising triumphs of human inventiveness - they made public health campaigning appear partisan and daft. In canteens and refectories in schools, hospitals, ministries of health and all the places where the health obsessives reigned people fled from dreary, joyless menus, low in sodium, sugars, fats and taste. The health industry drove eaters into the arms of the junk merchants.

Unless we change the way we formulate and promote our recommendations, people will go on rejecting them. For food is cultural. Eating is a cultural act. It nourishes not just the body but also the body politic. A healthy diet contributes not just to individual health but also to a healthy society - a society, that is, of diversity, tolerance and freedom, where people can enjoy occasional rational indulgences without finger wagging from the nanny state.

We eat to identify ourselves with other members of our communities. We cherish the foods of our traditions, our ethnicities and our childhoods. Dietary advice is doomed to fail unless it adapts to the history and sense of community of those to whom it is addressed. One might almost as well recommend shellfish to a Jew or pork to a Muslim as tell an Andalusian to stop frying or a Mancunian to forgo chip butties or a Deep South Mammy to deprive her children of well-larded collard greens.

Traditional foods are good for people: that is why they are traditional. They are good for the soul - for the sense of self - as well as for the body. By endorsing and encouraging them, we would help steer customers away from health-threatening environments such as the cheap burger joints and E. coli-coated salad bars. The important ingredient we need to add to traditional eating habits is moderation. While food remains cheap, people will probably go on eating too much of it. But they would be healthier if they ate less. The most effective slimming diet is a normal diet without overindulgence.

Tell me what you eat, and I will tell you who you are. The best next steps for health campaigners to take with the people they address are to respect them, acknowledge their priorities and tastes, and to adjust future advice to suit the cultural context.