Eating healthily taxes the willpower more than the intellect. You already know what to do; it's actually doing it that can be a struggle. Football fans chant about the perils of eating all the pies, but come the half-time whistle they queue up for a Ginsters. In this battle of wills, adults' better natures can need a bit of help - and the same is even more true of impressionable children. Youngsters received that with the ban that begins this term on school vending machines selling crisps, chocolate and fizzy drinks. This gives pupils respite from Coca-Cola, Nestlé and the rest; it also establishes a distinction between junk cuisine and healthier eating.

The Great KitKat Clampdown may sound footling, but it is part of a big political advance. Put it together with the public smoking ban and the expulsion from school of Turkey Twizzlers, and a picture emerges of an administration willing to flex its muscle against purveyors of public bads. As a health white paper put it in 2004, the government wants to "shape the commercial and cultural environment we live in", so that it is made it easier than now to choose a healthier lifestyle. Ministers can still be too timid and need public pressure (take a bow, Jamie Oliver) to stiffen their resolve. Some even mislay their principles, as Alan Milburn did when the former health secretary turned adviser to Pepsi. But the general direction of travel is clear, and the government can be called to account when it doesn't stick to it.

So here is an inconsistency politicians should iron out. The classroom may now be off-limits to the junk merchants - but they can still get at children in hospitals and sports centres. If any institutions are to promote healthy eating these should, yet the dreaded junk-food vending machines live on in these places, so that many hospitals and sports centres sell little but sugary drinks and fatty snacks. Some hospitals, such as Southampton general, give Burger King and the like prime position inside their buildings. One children's ward in Addenbrooke's hospital in Cambridge even has a "Burger King Takeout Night". It was uncovered this summer by the Soil Association, which found that sick children had cheeseburgers and fries brought up to them.

For a hospital to have a Burger King franchise is a big contradiction (a whopper, one might say). Nor can it be consistent for the government to crack down on junk-food advertising around children's TV programmes, but allow the same messages to be displayed during school swimming lessons. A good public-health policy needs to address these discrepancies and extend the no-go zones for junk food. That is surely obvious, even if it requires a bit of resolve. Rather like sticking to a healthy diet.