God knows how Rishi Sunak feels on mornings when he’s not eaten for 16 hours and there’s still over half a 36-hour fast to go. Better than I did, presumably. But I’m not sure. It was probably around that time on a Monday – when, as I understand it, his body would have entered the longed-for fat-burning stage – that Sunak exhumed the disgraced David Cameron and called that abomination a triumph. What day was it, I now wonder, that Sunak agreed to release a Home Alone-style Christmas video of him frolicking boyishly in Downing Street? Ah. It was “posted on social media at teatime on Monday”. Most weeks, we have learned, the prime minister stops eating on Sundays at 5pm and doesn’t resume until a day and a half later: 5am on Tuesday. The source who disclosed to the Sunday Times Sunak’s attachment to a system known to obsessives as a “monk fast” called it “a real testament to the discipline, focus and determination that he shows in all aspects of his life and work”. Confirming how much has changed since 2009, when a similarly disciplined approach was endorsed by Kate Moss: “Nothing tastes as good as skinny feels.” She was denounced for encouraging eating disorders and took a decade to live it down. Now that intermittent fasting has been normalised – thanks not least to that enterprising advice industry, Dr Michael Mosley – news of Sunak’s regime was well enough received for him to elaborate last week. The 36-hour fast is an “important discipline”, he told viewers of ITV’s This Morning, fresh from his latest starvation binge. It helps with his “balanced lifestyle”. That is, Sunak likes sugary things on days when he’s not consuming only black tea, coffee and water. It seems to me, having now tried the fasting part, an insanely high price to pay for the occasional bun and (his weekly) Coca-Cola. Especially when Sunak is, as emphasised by close-fitting shirts, thin: a walking provocation for politicians like Cameron and Boris Johnson, principally composed of wine and animal fat, who need so little encouragement to recite “Yond Cassius has a lean and hungry look” (the Etonian version of “I’m just big boned”). While Sunak’s idea of a balanced lifestyle will not tempt everyone, the boasts about exemplary “discipline” did feel like a challenge. Are people who manage their weight via more moderate methods less to be admired for discipline, and – if his supporter is correct – their “focus and determination”? Would we be better people if we, too, rendered ourselves hungry, nauseous, tetchy, distracted, tired, headachy and unavailable for shared meals every week? Do adults who similarly fast between eating junk, but only because they can’t afford a decent diet, also brag about ketosis? As a friend pointed out, comparable food restriction can also be achieved via a determined bender, though the impact, cognitive and otherwise, is less well explored in what is delicately called by researchers “an animal model”. Not that extrapolation from rat sacrifice comes close to validating Sunak’s diet. Much as their promoters like to claim myriad healthy, longevity-promoting boons of intermittent fasting, these are not yet confirmed in healthy humans. In fact, Professor Luigi Fontana, of the University of Sydney, an expert in nutrition and longevity, has called the best known example, Mosley’s 5:2 diet, “a wonderful marketing strategy”. Fontana conducted an intermittent fasting experiment on human subjects that showed, aside from weight and fat loss, “in terms of metabolic health, inflammation, insulin sensitivity, it doesn’t work at all”. Still, why not? I tried the Rishi fast, starting 9pm Tuesday, ending 9am Thursday. It’s not quite as bad as it sounds if you can lose yourself in something the first evening (thank you, All of Us Strangers) and spend around 14 out of the 36 hours asleep. The waking hours on the second day become roughly as crap as you’d expect, worse if you never drink black tea or coffee and are sustained by neither spiritual purpose, the rat model, nor the wisdom of Mosley. Though even Gandhi appears to have confirmed that fasting is always ghastly. That being the point. “Though I bear joyfully the pangs of hunger and many other discomforts of fasting, let no one imagine that I do not suffer.” After many nausea-inducing coffees and ditto black teas, the discomforts really kicked in around 2pm with a headache intensifying from 4pm when every second thought turned to food, especially, for some reason, fish and chips, or failing that, one miserable oat cake. Studies on Ramadan have found adherents struggling with distraction: they at least have a communal goal. Consuming irritability set in around hour 21, a bleak and punishing phase when it is to be hoped that neither Sunak nor any adopter in a position of responsibility ever risks an important decision. Or not without adapting the ancient Persian habit of drunk/sober deliberation, making it with cake. Being a pro, Sunak may not wake up grimly unrefreshed on day three, but he must have done, like all hungry fasters, once. Why persist? Given the many alternatives to bodily mortification, something not very rational must impel him to combine it with the weight of leadership. As for mental acuity, here’s the conclusion of one study: “There is no clear evidence of a positive short-term effect of IF [intermittent fasting] on cognition in healthy subjects.” Severe calorie restriction may even, recent research suggests, be associated with cognitive impairment. True, recalling Liz Truss’s sauvignon riders, Johnson’s partying and Cameron’s similarly 7-7 line in indulgence – he reportedly sacked a minister over a glass of red – the country is better off living with “Nothing tastes as good as Rishi feels”. But in case the renewed interest is endorsing the idea that 36-hour fasting is virtuous, sensible and really worth a try: it isn’t. Unless you’re literally a monk. Catherine Bennett is an Observer columnist