The 'Barbie' cast got in shape by intermittent fasting and quitting ultra-processed foods, their trainer said

• The cast of 'Barbie' did intermittent fasting and avoided ultra-processed foods to get in shape.
• Their trainer told Insider that eating mainly whole foods can boost energy levels.

The cast of "Barbie" didn't cut any food groups out of their diet to get in shape for the movie, but they did avoid ultra-processed foods and do intermittent fasting, their trainer said.

London-based personal trainer David Higgins has been working with the film's lead, Margot Robbie, for years, and trained all the Barbies and Kens with a mix of pilates and weight-lifting — including core circuits, and plank, push-up, and pull-up challenges — to complement their dance training.

Higgins also gave the cast nutrition guidance.

They weren't put on restrictive diets or given "cheat days," but were encouraged to make smart choices at weekends.

"I'd just say, 'Guys you know how to look after yourselves, you're all adults, have your weekends and I'll see you Monday,'" Higgins told Insider. "Everyone knows they're working on the biggest film in the world and that's a nice enough motivation."

The cast were asked to avoid UPFs

Higgins told Insider he doesn't believe in exclusion diets, apart from when UPFs are cut. "Ultra-processed food is not good for your body, it's just not. Once you get rid of that, your body thanks you: you're clearer, you sleep better, you're not as stuffy when you wake up," he said.

Eating fewer UPFs can also help maintain energy levels, Higgins said.

"If it comes wrapped in a package of plastic and it has to tell you what's inside of it and you don't even understand what some of the words are on the ingredient list, then it's probably ultra-processed, that's as simple as it gets," Higgins said.

Eating UPFs can lead to overeating

While lots of foods such as oats, yogurt, or flour are processed in some way, UPFs are generally mass-produced in a factory and contain additives, such as colors and preservatives to maintain taste or texture, and have been linked to various health problems such as cancer and dementia.

Examples include packaged cakes and cookies, and bags of chips. A good rule of thumb is to avoid foods with more than 10 ingredients or any that wouldn't be found in your own kitchen, according to epidemiologist Dr. Tim Spector.

Research also suggests that UPFs can lead people to overeat, with one 2019 National Institutes of Health study finding people ate on average 500 more calories a day and gained more weight on a UPF diet when compared with those who ate fresh food, as Insider's Hilary Brueck reported. The reason why is unclear but scientists believe there may be something unique about how our hormones interact with ultra-processed foods.

It's for this reason that Spector previously told Insider that people who want to lose weight should stop counting calories and instead focus on eating whole foods, which are higher in fiber and protein than UPFs and keep us feeling full.

They also release energy slowly, making us less likely to reach for more food soon after, Spector said.

The cast did intermittent fasting

Higgins also asked the cast to try intermittent fasting, meaning they would eat all their food for the day in an eight hour window and fast for the remaining 16 hours.

"I find it's a really nice and neat way to assist the body and teach the body it doesn't need fuel post 7 p.m. or before 11 a.m.," Higgins said. "If you can break that habitual eating pattern or cycle then you'll automatically see physical changes because you'll be resting, digesting, and your body doesn't need to keep digesting for hours and hours."

Higgins encouraged the cast to be flexible with their schedules. For example, if someone was going out for dinner, they could move their eating window later.

"Intermittent fasting for me works really well and I find great results across the board with that," he said.

Intermittent fasting can put a person in a calorie deficit without trying

Weight loss happens when a person is in a calorie deficit, but intermittent fasting can help them achieve that without trying, research suggests.

It doesn't work for everyone though — people who've tried the lifestyle before previously told Insider they found it unsustainable because they felt too hungry, struggled in workouts because of a lack of energy, felt the urge to binge eat, or found it hard to have a social life.

Weight loss aside, intermittent fasting has also been linked to reduced blood pressure, slower aging, and reduced risk of some diseases.