There is an image of what a top footballer eats, and that image looks like boiled chicken breast on a white plate, no salt, no pleasure, like a punishment. Toscana Viar, nutritionist to the Spanish national team, has spent seven years disputing that picture with the simplest possible argument: "What footballers eat is delicious, it has nothing to do with sad steamed chicken breast."

Viar was speaking after the World Cup win against Argentina. The first thing she said was: "The credit is not mine." That is a sentence rarely heard in that sport from someone with a name on the coaching staff.

In practice, her job looks different from what most people imagine. At major tournaments there is no single meal for everyone, but a buffet with a range most restaurants do not have. On it: turbot, ribs, boiled lentils, pasta carbonara, spicy vegetables with tomato, stuffed aubergines, menestra. There is ceviche too, rice in three flavours, carpaccio. None of those dishes looks like a regime.

The key is that the menu is not universal. Every player gets his own plan, according to position, minutes played, injuries, weight and what his body is asking for that month. The kitchen prepares all the variants simultaneously, and the player does not have to think - he takes what has been picked for him.

The most interesting part of her philosophy is what is missing from it: prohibitions. "There are no forbidden foods and, from time to time, you need to allow yourself an indulgence in order to switch off", Viar says. Pizza, champagne, sushi, burgers - all of it goes into the calculation, planned, not as a transgression. The reason is not leniency but psychology. A person living for months inside a closed regime does not survive on discipline without a small opening.

And the regime really is closed: "It is almost like Big Brother, because during the World Cup we spent 53 days together, 24 hours a day", she says. Fifty-three days in the same building, with the same people, with the same kitchen.

This is not advice for elite athletes. It is advice for anyone who ever started a regime on Monday, broke it on Thursday, and then gave up entirely because "I've already ruined it". The coaching staff of a world champion believe that for someone training every day, it is more sensible to plan the indulgence than to pretend it will not happen.