Rishi Sunak fasts for 36 hours at the start of each week, it has emerged.
The prime minister survives on a diet of water, tea or black coffee from 5pm on a Sunday to 5am on Tuesday, his friends say.
One said: “He is incredibly disciplined.”
A source close to the PM told The Sunday Times: “It’s true, he doesn’t eat anything at all on a Monday.
“It’s remarkable really given that he is often on visits or doing PMQ prep on a Monday. It’s a real testament to the discipline, focus and determination that he shows in all aspects of his life and work.”
Mr Sunak, 43, has spoken before about the practice – a key part of the Hindu religion – but the full extent of his fasting has not been revealed until now.
He previously revealed that his morning routine consisted of an early rise and a gruelling Peloton workout, followed by either no breakfast at all or a small one, such as Greek yoghurt and blueberries.
In an appearance on the Twenty Minute VC podcast last year, Mr Sunak revealed his preferred time to wake up was 6am.
He said he is a “huge fan” of Peloton workouts, especially those led by one of the brand’s most popular instructors, Cody Rigsby, and consequently, he listens to a lot of Britney Spears.
“I’m a huge Cody Rigsby fan. He has been my long-term favourite, which means you do have to listen to a lot of Britney,” Mr Sunak said, adding: “But you know, no bad thing in trying to get you motivated, I guess.”
When he is not taking part in a Peloton class, Mr Sunak opts for a run on the treadmill or a high-intensity interval training session at his local leisure centre.