Country star Carrie Underwood is so paranoid about gaining weight, she keeps a strict food diary in a bid to keep herself slim.

The singer admits that her obsession borders on Obsessive Compulsive Disorder (OCD) - which sees sufferers indulge in irrational, compulsive behavior.

Underwood often thinks of herself as ugly and refuses to leave the house without make-up. And she admits to following strict guidelines when it comes to her diet to make her feel better about herself.

She tells U.S. InStyle magazine, "I think about what I look like probably more than I should. But I think everybody is her own worst critic.

"Some days I step out of the shower, put my lotion on, and I’ll be like ‘Ugh, ew, ew.’ "If I put on five pounds, it’s noticed immediately. I’m OCD like that. I count calories, fat and fiber - which is important in making you feel fuller faster - and protein, especially when I’m working out."