What, exactly, is the government’s healthy eating advice based on? As expounded by NHS Choices and Change4Life, it resembles a lazy student essay cobbled together from out-of-date textbooks. The same old script - the one that says saturated fat is bad for us and carbs are good - is recycled interminably. As are a series of trite homilies: “Base your meals on starchy food.” “Why not swap butter in your mash for lower-fat spreads?” And so on.

It’s bad enough that official healthy-eating advice is both seriously misinformed and also misinforming (there are good grounds for thinking that swallowing the government’s prescription will shorten, not extend, our lifespan). But what is scandalous, even sinister, is the refusal of the dietetic establishment to amend its advice in the light of a substantial body of emerging data.

Just as a taster, a comprehensive review of 23 randomised, controlled trials - the gold standard for scientific data - has demonstrated that low-carb diets are more effective than low-fat ones for both weight loss and reducing disease markers.

“Why should we trust dietetics who get it wrong but won’t recant?”

Why aren’t we being told this? The most charitable explanation is that misguided paternalism prevents the Department of Health from presenting the public with scientific uncertainty. But perhaps the situation is just plain embarrassing. Public health advisers don’t relish the prospect of admitting that their guidance has been duff. The absence of any official acknowledgement that decades of advice suggesting eggs were bad for us were wrong tells you all you need to know about the bureaucratic appetite for correcting errors.

A further unpalatable possibility is that the UK’s dietetic establishment has been captured by food industry lobbyists, and that the grain pushers are simply better organised and funded than those who defend such foods as butter, full-fat milk and red meat.

The same reservation hangs over certain charities. The British Heart Foundation, for instance, is part-funded by Flora pro.activ, which disinclines me to heed its nutritional counsel.

Public confidence in official healthy eating advice is at an all-time low, and no wonder. Why should we trust people who get it wrong but won’t recant?

Joanna Blythman is a journalist and author of What to Eat.