Christina Aguilera
Christina Aguilera acknowledges the applause at the end of her display for Dsquared2 in 2004 Reuters

Stars are under a lot of pressure to be thin these days, and like most women, they too struggle with their weight. The media, fans, and even other celebrities hold these women to a standard higher than what may be normal. If they gain a pound, or lose one, they are considered too fat, or too thin. And it doesn't help when other stars say they are "fat."

On a recent episode of E!'s "Fashion Police" Kelly Osbourne took some enjoyment in Christina Aguilera's recent weight gain calling Aguilera "fat."

"Maybe she is just becoming the fat b**** she was born to be. I don't know. She was a b**** to me. And she bought my house!"

And Osbourne didn't stop at that. "She called me fat for so many years," Osbourne continued, "so you know what? F*** you! You're fat too."

The reality star, and daughter of Ozzie Osbourne wasn't shy to talk about her issues with weight, either. "I took more hell for being fat than I did for being an absolute raging drug addict. I will never understand that."

Another celebrity who has felt the constant need to be a size zero is Kim Kardashian. The reality television star stated on a recent episode of "Keeping Up With The Kardashians," "My career is doing ad campaigns and swimsuit photo shoots. People don't understand the pressure on me to look perfect.

"When I gain a pound, it's in the headlines. Imagine what the tabloids would do to me if they saw all these spots?" The 30-year-old Kardashian was recently diagnosed with psoriasis, a skin disease which causes rashes to appear on the body.

Last month Jessica Simpson had to shoot down rumors that she was pregnant after photos of her surfaced looking more curvy than usual. "This photo agency is full of malarkey," her publicist reportedly said. "She is not pregnant."

And on the opposite side of the spectrum is Kate Middleton, who many believe is too thin. After the Royal couple toured North America, statements of Kate being "too thin" began to circulate. Kate was seen standing beside Nicole Kidman, and looked surprisingly skinnier than the tall and lean Kidman. Anorexic rumors also started brewing, though Kate has not been diagnosed with an eating disorder.

The reality is that these women are constantly in the spotlight, and their weight will fluctuate, especially with age. The once rail-thin Aguilera is no longer an 18-year-old teeny bopper who lives her live performing on-stage. It's understandable that celebrities, like other women, will not always remain a size zero.

Must Read: Kim Kardashian Revealed Secrets Before Wedding (PHOTOS)