Kristin Cavallari feels "too thin".
The former 'The Hills' star has revealed she is trying to bulk up after giving birth to her sons, Camden, two, and eight-month-old Jaxon, with her husband Jay Cutler, as she doesn't like looking too skinny.
She said: "I don't know why or how but after I had children my body literally changed and now, for me, it's about trying to keep muscle on so I don't look too thin.
"Because it's very easy, especially because I have no curves, that I can look really skinny and I don't like that look."
The blonde beauty, 28, insists there is "no secret" to her impressive figure and tries to "workout four to five times a week" and stick to an "incredibly healthy" diet in order to stay in shape.
She told E! News: "There's no real secret, I work my butt off in the gym...[but] I'm trying to gain some muscle so I've been working out with really heavy weights...and then I drink a protein shake right afterwards."
Kristin is also helped by her NFL quarterback husband, 31, who is always giving her "workout tips."
She said: "He helps with giving me certain moves. Like I want to make my butt bigger so he's telling me what to do."