MPs should not go on reality TV. The results are conclusive. George Galloway shouldn’t have gone on Celebrity Big Brother: 13 years later, the image of Galloway pretending to lick milk from a bowl held by Rula Lenska, another contestant, still overshadows in most minds anything else he has ever done.

Penny Mordaunt shouldn’t have gone on the diving show Splash: like it or not her political legacy will now include one spectacular belly flop, lovingly captured and replayed in slow motion from four angles during the show. And Nadine Dorries shouldn’t have gone on I’m a Celebrity Get Me Out of Here, for which she was suspended from the Tory party, just a few days before she was humiliatingly booted out of the jungle itself.

It is therefore difficult to imagine what has possessed Dorries – at this serious time in national politics – to go on another reality TV show. This one, ITV’s The Junk Food Experiment, marketed itself as a pseudo-scientific investigation, feeding five celebrities nothing but pizzas and fried chicken and seeing what happens. This is both a tired idea and a disgusting one, and involves, as all of these types of programmes do, close-ups of celebrity meat sweats, close-ups of open-mouthed chewing, and a bit where burgers are whizzed up in a blender.

Much of the programme is dedicated to discussing Dorries’ bowel movements, which feature both in coy voiceover (“Nadine has always had a cordial relationship with her lavatory, but this diet has definitely led to an outbreak of hostilities …), and from the source herself (“I’m passing rabbit pellets!”) as the camera pans grandly across the Palace of Westminster. At one point she produces a stool sample in the loo of her House of Commons office (the camera films the toilet door during the process, waiting for the flush), and later sits at her desk as she is given the results over Skype.

Dorries claims she is doing it to raise awareness of obesity – a good idea, in theory – but the viewer may wonder whether her job as an MP might be an even better platform from which to do this – particularly at the point in the show where she has eaten so much junk food that she cannot remember her House of Commons speech on obesity. It is a rare politician whose career is helped by public humiliation. Can she really hope to wield greater influence on obesity legislation now that ITV viewers have seen her stool samples?

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Politicians who go on reality TV tend to justify it in three ways. Raising awareness for some cause, starting discussions about politics, or to “humanise” politicians. All three are flawed. MPs are in possession of far more power than most to champion a particular cause – it is a waste of their time to “raise awareness” in such indirect ways as charity challenges or TV shows. Any attempt to discuss politics will probably be cut out by producers. And the public tend to want their MPs professional and capable, not eating kangaroo testicles. Humanisation is overrated, particularly when it involves time away from politicians’ real jobs (or “day jobs” as Dorries’ is referred to in The Junk Food Experiment).

The real reason Dorries is on the programme may instead have been revealed quite accidentally, as she introduced herself to Peter Andre in the first few minutes of the programme. “You don’t know who I am do you?” she said cheerfully, as Andre searched his memory. “I’m Nadine. I was in the jungle?” Politicians who go on reality TV do it for one reason: vanity.

• Martha Gill is a political journalist and former lobby correspondent