|Olivia Wilde and Jason Sudeikis|
The 37-year-old actor credits his gorgeous fiancée, who previously revealed they "have sex like Kenyan marathon runners", for helping him to slim down by enjoying daily workouts with him under the sheets.
The 'Saturday Night Live' star told the August issue of ELLE magazine: "The truth is, I'm not getting up an hour earlier and walking on a treadmill. I have the greatest workout partner in the world. And you don't need a gym membership for that kind of workout."
Jason, who began dating the 29-year-old actress in November 2011, has also made a number of changes to his diet.
He explained: "A lot of it comes from tiny things, like not eating barbecue sauce with my pizza at two in the morning. I think it's all a manifestation of being happy and wanting to treat myself well."
Despite being comfortable to share details of his love life, Jason admits losing his virginity was scarier than his first appearance on the comedy sketch series.
He said: "Sex was probably scarier. I wasn't as concerned that my parents were going to walk in in the middle of my first sketch. There are security guards there. That's a big part of it."
Jason and Olivia, who announced their engagement in January, reportedly plan to tie the knot in New York next spring.