The world's heaviest man is set to reveal his weight-loss tips in a new autobiography.

Paul Mason, who now weighs in at 700-pounds, left the hospital Wednesday night in an ambulance after undergoing life-saving gastric bypass surgery.

The former postman from England had to drop 280-pounds from his 980-pound peak last year before he could have the operation, which limits the amount of food going into his stomach.

"He's been telling people in the hospital how he's writing this book and it will reveal how he's managed to lose so much weight,” a source told The Sun. “He's been in good spirits."

Mason started writing as he recovered from the operation at St. Richard's Hospital in Chichester, West Sussex, where he stayed for three weeks.

He used to consume an astounding 20,000 calories a day, which is eight times what the average man eats.

He got so big that firemen once had to knock down a wall so he could be taken to hospital.

Despite his weight loss he is still thought to be the world's heaviest man.

Previous record holder Manuel Uribe, 43, of Mexico, shed more than half of his 1,200-pound bulk to get married last year.

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