"The phone is pinging. Ping ping. I was going to bed at 1am consistently and getting up at 4am or 5am. It caught up with me."
The 'Friday Night Feast' star knew things had to change and now makes sure he gets to bed by 10pm, in a cold room and wearing an eye mask to block out light.
He told The Sun newspaper: "I was studying nutrition and I realised the most powerful exercise in the gym is sleep. And the most powerful part of nutrition is sleep. Everything comes back to sleep."
"[Now] I'm like a baby, I have to set an alarm to go to bed. I'm 43 years old and I've got to put myself to bed. But I changed my habits and the difference is amazing."
In 2017, Jamie injected £13 million of his own money to save his Jamie's Italian chain - which still saw 12 out of 37 branches close - and months later, his Barbecoa restaurants went into administration, he closed down his Union Jacks eateries and stopped publishing his Jamie food magazine.
And the chef admitted it was the lowest point in his life.
He said: "It was definitely the worst time in my life."
But the star remains positive and credits his wife for all the "good" things in his life.
He gushed: "She's my best mate. There nothing good I've ever done that hasn't come from how we are as a unit."
Jools has admitted she's keen to have another child but Jamie thinks their brood is "enough" - though he won't completely rule out expanding their family again.
He said: "I'm going to try to control that one . . . but I have to try to control myself, which I'm not very good at.
"I do think five is enough but everyone keeps telling me that six is a round number."
