The Manchester United has stated that he returned to the training ground heavier than he expected to be after having a few "bevvies" on his holiday, but says he is naturally stocky
The England international has published a book entitled 'My Decade in the Premier League' with excerpts of his biography being published in the Daily Mirror.
The striker admitted: "I'm like most blokes, I put on a few pounds after a holiday.
"Even if I don't train for a week, I put on two or three, but when I get back to Carrington [Manchester United's training ground] for the first day of work, I'm in for a shock.
"The scales in the club gym tell me I've put on a few more pounds than expected - seven. Seven!
"Then I remember - I drank a few bevvies [beverages] while I was away. I'm stocky. I'm not like Ryan Giggs, all bone and lean muscle."
"As a striker I need to work hard all the time. I need to be sharp, which means my fitness has to be right to play well. If it isn't, it shows."
Rooney's boss, Sir Alex Ferguson, admitted that his striker needs to take care of himself, but defended his player's attitude towards fitness.
"Wayne is no Ryan Gigs," Sir Alex acknowledged. "Ryan has never put a pound on in his whole life.
"Wayne is a boy that needs games, you can see that from the frame he's got. He is stocky, strong and really needs games, simple as that."