She is famous for her voluptuous figure, often outshining the 'size zeroes' on the red carpet with her killer curves.
Which is perhaps why the actress was out pounding the pavement, working up a sweat with a jog alongside her new boyfriend Sean Penn.
Scarlett's rounder stomach was noticeable under her tight exercise gear, a small bump protruding beneath her grey vest and black lycra leggings.
The 26-year-old went incognito in a cap and sunglasses, keeping her head down as she concentrated on her workout.
She stood out, though, in her bright pink Vibram FiveFinger sport shoe, designed to imitate barefoot running.
Sean, 50, was more casual in a T-shirt and jogging shorts and regular trainers.
The pair were joined for the jog near Penn's Malibu home by friend Owen Wilson, who puffed away behind the couple in a long sleeve T-shirt and shorts - the boys soon powered ahead though, leaving Scarlett trailing behind in their wake.
The He's Just Not That Into You star's rounded stomach has led to some internet speculation that she might even be pregnant, although it could just be down to some unforgiving tight clothes and a big lunch.
A pregnancy would come as just as much of a surprise as the couple's romance - the pair, who have a 24-year age gap, were first linked together back in January, just weeks after she announced her divorce from her husband of two years, actor Ryan Reynolds.
And Sean's ex-girlfriend Jessica White appeared to confirm the relationship in a recent interview.
'I think Sean needs a good woman in his life,' Jessica told entertainment website Popeater.com. 'They're great together.'
Owen, Sean and Scarlett are all friends of director Woody Allen's, though it is unclear if it was he who introduced them.
Scarlett is a muse to Allen and starred in two of his films, Match Point and Vicky Christina Barcelona, while Owen stars in his latest, Midnight In Paris.
