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A quick glance at Karlie Kloss’s Instagram feed reveals the top model is the picture of health. When she’s not posing as the face of Swarovski or attending classes at New York University, the former Victoria’s Secret Angel is busy in the gym, alternating between boxing classes, Soul Cycle, and Pilates. But in a recent interview with The Cut, Kloss’s trainer reveals her secret to good health isn’t solely because of her workout routine.

Anna Kaiser is the founder of AKT fitness center in New York City and regularly trains Kloss, along with other A-list celebrities like Sarah Jessica Parker and Shakira. While she is best known for her hybrid workouts which include yoga, dance, plyometrics, and strength training, Kaiser reveals that the secret to good health is honing your nightly routine, which should include seven to eight hours of sleep.

“Working out harder or better or eating less isn’t the answer. It’s about getting enough sleep,” she says. “If you have a choice where you’ve only been sleeping five or six hours and can sleep an extra hour or work out, sleep an extra hour.”

Kaiser explains that healthy sleep habits do more than help her clients start the day feeling well-rested. “Five to six hours for a week really prohibits your cognitive and hormones functions,” she says. Any less and “you’re running your body down, which will affect your energy and hold onto excess water and weight. It will make you hungrier.”