Emmerdale star Lucy Pargeter joined in, telling Willerton that pressure on young girls to look a certain way had made her "ill" when she was young.
Adlington added: "And it's also making me very, very insecure that I have to look a certain way. For me, I was an athlete, I wasn't trying to be a model, but pretty much every single week on Twitter I get somebody commenting on the way I look."
The swimmer was comforted by former EastEnder Laila Morse, who told her she was "beautiful", saying: "Much better than her. A hundred times, do you hear me?"
Willerton, who represented Great Britain at the Miss Universe 2013 pageant, has regularly appeared in the camp in one of her bikinis.
Adlington told Morse the model "doesn't know what it's like on a day to day basis".
She said: "She's stick thin, she's got these push-up bras that make her boobs seem massive. She's stunning."
The new series of I'm A Celebrity... Get Me Out Of Here! begins tonight in typically dramatic fashion as the two teams race each other across a snake-infested island in a bid to win one last night of luxury.
Among the celebrities taking part is Conservative Nadine Dorries, who is the first sitting Westminster Member of Parliament to participate in a reality television show since George Galloway's appearance in Celebrity Big Brother in 2006.