Alicia Silverstone
Alicia Silverstone shot to fame as a spoiled valley girl with a heart of gold in the 1995 comedy classic Clueless. Off screen, the then-18-year-old was battling severe asthma, insomnia, full-blown acne and constipation.

Nearly three years after that film, Alicia switched from a "steak and doughnut diet" to a vegan lifestyle. Now, at 33, she says she sleeps like a baby, doesn't worry about her weight and has tons of energy. "I used to have all those white marks on my nails and they were very brittle, and now they're so strong I cannot bend them," she says. "My eyes got really white, and I feel like I look less puffy."

Still, becoming vegan wasn't an overnight transition. An avid animal lover, she says she had flirted with vegetarianism since childhood. "When I was 8 years old, my brother was making the noises of the animals I was eating, so I decided to go vegetarian," she says. "Then I would give up because I was 8."

At 21, Alicia says she saw a documentary about how animals were raised and slaughtered. "I just took a look at my dog and said, 'If I'm not willing to eat you, how can I continue to eat these other creatures that have the same desire to live, are just as funny, just as cute as my dogs?'"