The supermodel, who is dating Leonardo DiCaprio, has been modelling since she was a child.
Refaeli wrote on Twitter: "I get so sad when I see 15-year-old pale extremely skinny models at the agency looking all shaky and hungry… when will it end?!?!? (sic)"
The 25-year-old also condemned plastic surgery.
She added: "Seriously… Plastic surgery is not helping your impact on young women or your looks!… Some people are addicted to drugs and others addicted to alcohol. Me? I'm addicted to pomegranate juice."