The `Glee` actress - who plays cheerleader Quinn Fabray in the musical drama series - believes ensuring she sticks to a regular routine and gets plenty of rest is the main factor in looking good and staying in shape.
She said: "We do a lot of dancing on the show and that`s enough to keep the weight off.
"Plus in Los Angeles, everyone eats really healthily and I also sleep a lot - that`s a key factor.
"I`m happy with my body but don`t feel the need to stay trim."
Dianna - who has previously dated British actor Alex Pettyfer and `Gossip Girl` star Sebastian Stan - also revealed she loves spending time in the UK as she can visit her favourite shops.
She added: "I came to the UK for the first time a few years ago and spent two weeks in London.
"Like all Americans, I love Topshop.
"We have one in the States but it`s not the same as the one in the UK. I really love it here."