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Rihanna, Alexandra Burke, Rochelle from The Saturdays are among a numbers of stars fuming at tweets from reality TV star Kenneth Tong.
The Big Brother contestant is criticising women who aren't size zero.
He's been using Twitter to post messages about his "Size Zero Pill and Campaign" and has been a world wide trending topic but celebs are not impressed.
Tong's tweets include "Thankful for this global opportunity to help girls all over the world know that to be skinny is to be perfect & to be fat is unacceptable."
Rihanna snapped back: "This is exactly why girls are doing everything to destroy their bodies! Girls are dying all over the world because of ignorant individuals like this!"
She later added: "Young ladies, love yourself! Your skin, your booty, your hair... You're all beautiful! Keep your hearts pure! Love and laugh, and live life," which was retweeted by Katy Perry who added: "PREACH!"
Rochelle of The Saturdays said: "Your tweets are upsetting a lot of people, including myself! It's very vile! Twitter isn't meant for people like you!!"
Alexandra Burke added, "It isn't nice to make other girls feel inferior . How dare you put others down! No one follow this guy Kenneth ... It just isn't cool."