For more than two decades, South African–born actress Charlize Theron has starred in films ranging from dramas like The Cider House Rules and The Astronaut’s Wife to action films like Æon Flux and Atomic Blonde. A common factor in all of these has been her great beauty and phenomenal physique.

This is no accident. “Charlize is an extremely serious, focused, professional, no-B.S. client,” said her fitness guru Fedele De Santis. “She’s so tenacious, my nickname for her is Thundercat!”

According to Charlize herself, maintaining her physique — and attitude — isn’t easy. “Life is just as complicated for me as it is for any other woman out there,” the mom of two has said, “and I wake up just like every other woman sometimes and can’t fit into my jeans and feel fat and ugly and have bad days.” Fortunately, the 43-year-old has found the key to motivating herself.

charlize theron
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When Charlize is preparing for an action role, De Santis tones and strengthens her with pushups, bench step-ups, bicycle crunches, kettlebell squats and dumbbell deadlifts, among other exercises. However, when she’s on her own, Charlize enjoys less punishing activities.

“My mom recently got me to play tennis, which I wasn’t good at but really enjoyed,” she said.

Tennis is an excellent choice, since it provides a full-body workout, burns fat, strengthens bones, increases flexibility and balance and is good for the heart. It also provides both aerobic and anaerobic exercise. Briefly, an aerobic workout burns oxygen and sheds pounds while the higher-intensity anaerobic workout relies on chemicals like glycogen for power and boosts metabolism.

Charlize also looks forward to hitting the yoga mat hard, doing two 90-minute power yoga sessions per week. The discipline relies on fast-moving poses that work up a sweat. She also takes up to four spin classes a week. Both are serious calorie burners. “If you do exercise you enjoy, you’re keeping yourself fit without even realizing it,” she stated.

Charlize tries to provide healthy foods for herself and her children. She avoids oily, processed foods, such as chips, French fries and pizza. She focuses instead on protein-packed vegetables, dark-colored greens and fruits.

“I have juices and kale and green salads every day,” she revealed. “When I’m eating healthily, getting enough sleep and not drinking alcohol, that’s when I look my best. That’s when I’m happiest and I think it shows.”

Charlize is also a proponent of “grazing” and says, “I eat six small meals a day.”

There are many benefits to this approach. Eating smaller meals helps with weight loss since the body doesn’t go into “famine” mode, which increases fat storage. Grazing intelligently also raises energy, since regular consumption of protein and healthy carbs stabilizes blood sugar.

But even a determined health seeker like Charlize occasionally splurges. “If I fancy a burger, rather than deprive myself I’ll have a quarter of one,” she admitted.

The psychology of a little indulgence can be beneficial too, since it tends to make you less cranky. In fact, when Charlize looks back on her life, there’s one proactive, curative lesson she wishes to share: Be good to yourself.

“I was in such a rush,” she said, “it put me in a constant state of anxiety. I wish I’d taken the time to enjoy everything.”