The 19-year-old actress defended the 22-year-old singer in a lengthy blog post after critics slammed Gomez for her perceived weight gain. Many called Gomez "fat" or worse after the former Disney star was photographed in a pink bikini earlier this month.
"Everyone is always saying how we shouldn't judge each other, so why are you commenting on a gorgeous, talented and smart young girls body when she's on the beach having fun with her friends AND SHE LOOKS AMAZING," Breslin wrote on Tumblr.
"How are young girls supposed to grow up normally and not feel bad about themselves and not developing eating disorders if it's literally national headline news that a THIN girl may or may not have put on a few pounds, and YET still remains THIN?" she continued.
"I think if we all took the time we spend making each other feel bad about ourselves and used it to make each other feel good, the world would be a better place," she opined. "Selena, you look amazing and more importantly look like you're having fun. Keep rocking those bikinis."
Gomez previously responded to the criticism by sharing a swimsuit photo of herself on Instagram, and captioned the picture, "I love being happy with me yall #theresmoretolove." The photo received over 1.4 million likes.
Breslin is best known for portraying Olive Hoover in Little Miss Sunshine (2006), and also starred in Zombieland and Ender's Game. The actress is scheduled for Maggie with Arnold Schwarzenegger, and will play Sarah Tourse on new Fox series Scream Queens.