You might assume Victoria's Secret model Marisa Miller was born beautiful. And yes, she's the first to admit her DNA is one explanation for her fresh-faced, glowing beauty. "But a lot of people believe that because I'm curvy—and blonde—I've had a boob job or some other kind of plastic surgery, which isn't true," says the 30-year-old California native. "I'm 100 percent natural, but I have to work hard to stay in shape. There's no magic pill. Believe me, if there was, I'd know about it."

1. Get active, and the sooner the better. "You could say I've been going to the gym since before I was born," says Marisa with a laugh. "I have a photo of my mom the day before she went into labor with me wearing her unitard and leg warmers—very eighties." Her mother's dedication to physical fitness, as well as both parents' passion for surfing, have contributed to Marisa's health mantra: "Working out is not a luxury, it's a necessity."

2. Never run on empty. "I usually have steel-cut oatmeal with sliced bananas in the morning, but if I want something fast, I whip up a protein shake," says Marisa. "I mix soy or almond milk, yogurt, a banana, and a scoop of protein powder with frozen organic fruit, like mangoes or blueberries. I don't measure anything; I just throw it all in the blender. I also carry Gnu Flavor & Fiber bars with me in case I need to eat on the run."

3. Give in to temptation. "I prefer healthy food and try not to bring too many treats into my house. But I don't believe in depriving myself either," says Marisa. "When I go to the movies, I have a sugary soda, not a diet one. And if I want a burger, I'll have a burger. I just make it a point not to eat one five days in a row."

4. Be flexible with your workouts. "It's not easy for me to stick to a set routine, but if I can do something almost every day, I don't have to play catch-up before a big photo shoot," says Marisa. "I have a home gym and I take Spinning classes at my local health club. When I can, I box with a trainer, which helps me blast calories. If I'm going on the road, I bring resistance bands with me so I can strength-train anywhere. Every bit helps."

5. Don't eat like your guy. "My husband, Griffin, is tall and lean, so he can eat anything he wants," says Marisa. "Some nights he'll bring home french fries, and I have to resist them! I decide to say ‘no' and then make something else, like a veggie burger. It's not always an easy choice, but it's a healthier one."

Check out the summer issue of Shape for the rest of Marisa's simple look- and feel-fabulous secrets, along with an inside look at her surf-inspired workout.