For those who have even the smallest pinch of spare flesh, the latest health study to emerge from the US, declaring half of fat people are just as healthy as slim people, makes you want to run straight to the nearest baker and buy a celebratory cream puff.

After all, we've spent decades being hammered with the notion that being even slightly porky is wicked. The idea is so entrenched that in a comparison of two people, one slim and one fat, the thin one would probably have to be grey and pustulated to be judged least healthy. So let's enjoy a small hallelujah before the next sobering expert comes along to inform us otherwise. Among the revelations from this University of South Carolina research is the fact some fat people remain "metabolically healthy" even though their body mass index would suggest they are not. Additionally, among those with heart problems, those who are underweight are worse off than those who are fat. Though I'm not very fat myself, this seems of particular relevance, since, last week, my five-year-old son asked me the mortifying question, "Why am I slim and you big?" I tried to suggest that this was because I was older, but he retorted, "But daddy's slim too and he's older."

Rather than deluge him with my own private torrent of indignation and pointing out that I do running, unlike his dad, or that I do eat quite healthily – a fact which he seems already to know, since he assumes that anything I like must, horror-of-horrors, be healthy – I simply hurled the word "metabolism" at him. My son is a bit sceptical about "healthy things", but nevertheless he seems to have gleaned that it's better, in this world, to be thin than fat.

A study like this one is hardly going to reverse that. But at least it provides a puncture to the bloated body of thought that suggests fatness is immoral, irresponsible and downright bad.