In a candid interview with Seventeen Magazine, Bella explained, "I eat a lot of pizza and really unhealthy food. I definitely gain weight and I'm not naturally thin. I'm really self-conscious if I go to trainers, so I just do stuff on my own. I go on the treadmill or do yoga and Pilates if I can."
Meanwhile, her sister Gigi "can eat whatever she wants. It's really annoying."
But Bella said that despite the fact that they share the same career, the two aren't competitive with one another.
"I just have to remind myself that she's been doing this forever," Bella said. "I can't keep comparing myself to her because we're so different. But people still love to compare and contrast us — what's better about her or what's not that good about me — and it's hard because people are really mean. But I'm her biggest supporter, and she's my biggest supporter. We're not competitive at all."
Bella also gets compared to another famous face: Jennifer Lawrence. And that seems to be a comparison she could do without.
"I never saw it. But there are some photos that it's really weird and we look very similar," Bella admitted. "People say it all the time. I'll walk onto set and five people will say, 'You know who you look like?' and I'm like, 'Jennifer Lawrence?' Then they'll say, 'How'd you know I was going to say that?' and I'll go, 'Because I hear it five times a day.'"
You can find out what else Bella had to say about her famous family and her rising career in the new issue of Seventeen, which hits stands Tuesday, Oct. 20.
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