Rishi Sunak said he uses intermittent fasting as a “reset” and a “detox” after an “indulgent weekend”.

The Prime Minister tucked into chicken Milanese during a visit to ITV’s This Morning studios on Tuesday, where he admitted he had already had his “second pastry” of the day.

He typically does not eat on a Monday, snacking only on “the odd nut”.

He told programme hosts Rylan Clark and Rochelle Humes: “I wish I was as disciplined as has been reported, is the first thing to say.

“So, like all of us, I start the week with the best of intentions, and then you hit contact with reality at some point.

“I try on a Monday, after a indulgent weekend, to try and have a day of fasting.

“It’s not totally nothing but largely nothing. I do have the odd nut, that kind of thing.

“I start with the best of intentions… we all do, right? And then things happen.”

He added: “My problem is I love sugary things. I eat a lot of sugary pastries, and all the rest of it, the rest of the week. And I like my food.

“I don’t exercise as much as I used to because of the job. So a little reset at the beginning of the week, a little detox.”

However, any fasting diet like this should be approached with caution, and many health professionals are dubious about the touted benefits.

– What is intermittent fasting?

Instead of just focusing on what you eat, intermittent fasting encourages people to think about when you eat. The idea is, you only eat during a specific time period, the theory being that this gives your body a break from digesting food.

Some people claim that intermittent fasting mimics the traditional eating patterns of our ancestors, who would have had to fast because of lack of food availability until they had hunted or foraged for it.

It is recommended to replenish the body with enough of the right nutrients whenever the fast is over.

– What are the different types?

People are advised to speak to their doctor before trying intermittent fasting, because some fasts could be more taxing on the body than others.

There is the 16:8 plan, where people only eat during an eight-hour window but fast for the remaining 16 hours (including the night time) – for example, eating between 10am and 6pm, and then only drinking water, milk, tea or coffee for the remaining time. Some opt for a longer eating window of 10 hours.

The 5:2 diet is also based on the principles of intermittent fasting – only consuming 500 to 600 calories for two days each week, and then eating a normal, balanced diet on the other days.

Alternate-day fasting is considered one of the more extreme approaches, and may not be safe for everyone.

A weekly one-day fast, similar to Mr Sunak’s method, is known as the eat-stop-eat diet.

– What are the pros and cons?

There are limited studies into intermittent fasting and its supposed benefits, so health professionals simply do not know enough yet.

A 2023 study by the University of Illinois Chicago found intermittent fasting is “as effective as counting calories” – when limiting food to a eight-hour window.

The study found that weight loss wasn’t dramatic, but that people were more able to stick to the plan consistently – compared with calorie counting.

Research published by the University of Glasgow, Teeside University and the Independent Public Health Consultant in 2018 suggested intermittent “energy restriction” may be an effective strategy for the treatment of overweight and obese adults – and more effective than not doing anything.

A previous study published in 2013 examined the results of fasting for 24 hours.

The researchers studied 16 people who fasted (but could eat 25% of their daily calorie allowance on fast days), compared with 16 who did not, over three months. The fasting group did show reduced weight, body fat and improved markers for cardiovascular disease.

Fans of the practice claim they feel various benefits, from a boost in memory and cognitive function, to improved blood pressure, better blood sugar control and weight management.

But negative side-effects have been reported too, including insomnia, irritability, headaches, light-headedness, digestive issues, poor concentration and nausea. It will come as no surprise that hunger is also a side-effect.

The idea is that, when you go hours without eating, your body eventually runs out of stored sugar to use, and it begins to burn fat to produce energy instead. But going for very long periods, over 24 hours, is more controversial – it might cause the body to think it is in starvation mode.

In addition, findings by the University of Toronto, published in Eating Behaviors in 2022, linked intermittent fasting with disordered eating and potentially dangerous, compulsive behaviours in young people.

Intermittent fasting is not recommended for people who are pregnant, have type 1 diabetes or have a history of disordered eating. Anyone with pre-existing medical conditions should consult their GP before making any major changes to their diet.