In 1902, the US government’s top food chemist, Harvey Wiley, was granted funding to investigate the effects of chemical food additives. He recruited 12 USDA employees, promising them $5 a month and a free lunch daily. The lunches were laced with borax, saltpetre, benzoic acid, salicylic acid, copper sulphate and formaldehyde. Each man was given a thorough physical examination and questionnaire before and after each meal to note the effects. Predictably, they got ill.

“Common sense, experience and intuition also have a role”

Nowadays, nutrition experiments involving even fewer participants are prime-time TV. Journalist Michael Mosley kicked off the trend with a BBC Horizon programme: a one-man experiment testing the effects of intermittent fasting. Whether or not he established the transformative power of fasting is a moot point, but that doesn’t matter: the ratings were great, and the resulting book made money for its authors, one of whom was Mosley.

Commissioning editors are currently obsessed with the “It’s 1am and I’m starving” video diary format, wherein a dishevelled bloke plays lab rat. Or why not two? In Horizon’s latest effort, the van Tulleken twins were enlisted to test the relative health impacts of sugar and fat. It won’t surprise me if there’s a spin-off ‘ratio diet’ book, since the take-home wisdom seemed to be that you can eat whatever you like, as long as you avoid foods with the demon 50/50 ratio of sugar to fat.

What nonsense these programmes are. To play the scientific evidence game you must first accept that for an experiment to have any value whatsoever, it must follow a statistically significant number of participants over a sufficiently long period of time, by way of a randomised intervention trial. Even then, only a meta-analysis of trials is robust.

Pop science is the pits, but debates on nutrition should not be the exclusive domain of scientists, however well-designed their experiments. Common sense, experience and intuition also have a role. It was blindingly obvious that Wiley’s 12 volunteers would sicken on their diet of toxins, just as it’s easy to predict that people won’t thrive long-term on a diet that consists solely of Krispy Kremes. If we wait for science to ‘prove’ it, we’ll wait forever.

Joanna Blythman is a journalist and author of What to Eat