"I've put on a good 11 pounds every series," she said. "The first couple of episodes it's 'No thank you, not for me'. Cut to the semi-final and we're hoofing up whole quiches."
Mel, who presents the hit baking show alongside Sue Perkins, revealed that her daughters have taken on the role of judges Mary Berry and Paul Hollywood when she recreates the show's magic at home.
"My daughters have become little judges," she said. "If I do produce a baked item, they tut at the soggy bottom and advise me to try harder next time."
As well as the perilous pull of cakes and bread on set, Mel also revealed another problem that the cast and crew face while filming.
The series is shot in spring in a "freezing" tent and the "main concern" is to keep 'Queen of Cakes' 78-year-old Mary Berry warm.
"She had four thermal layers on and two water bottles down the trousers," Mel explained to the Radio Times ahead of the second episode of the fourth series.
"This year we discovered these marvellous heated belts called 'hot trusses'. I was a big fan. They keep your stomach in as well, which is useful as the series goes on."
After the first episode of the new series, which was watched by 5.6million viewers, there are 12 contestants left in the competition.
In the first week of the competition, the hopefuls were instructed to produce simple sandwich cakes. This week they will attempt to impress the judges with their bread making skills.
Click here to meet the contestants.