Jason Sudeikis' weight loss due to sex with Olivia Wilde

AN actor has had a noticeable weight loss and is not shy in explaining why.

"I have the greatest workout partner in the world," Jason Sudeikis, star of NBC's Saturday Night Live and 2011 film Horrible Bosses , tells Elle magazine's August edition.

Sudeikis is crediting his fiancée, actress Olivia Wilde, for his lost weight.

"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," he said.

"And you don't need a gym membership for that kind of workout."

Wilde, who starred in TRON: Legacy and last year's movie In Time, has also been vocal about her sex life with Sudeikis, previously informing Us Weekly how they "have sex like Kenyan marathon runners.".

Sudeikis also credited other factors for his trim figure.

"A lot of it comes from tiny things, like not eating barbecue sauce with my pizza at two in the moing," he said.

"I think it's all a manifestation of being happy and wanting to treat myself well."

Wilde, 29, previously married to filmmaker and musician Tao Ruspoli, and 37-year-old Sudeikis plan to get married next year.

Charlie Day as Dale, Jason Sudeikis as Kurt and Jason Bateman in the comedy .