The Girls Aloud singer - who is a slender UK size 10 - insists she has insecurities about her body but dresses carefully in order to hide her flaws.
She said: "I hate my muffin tops - that's why I like leggings. They're good at disguising them. People never believe I have muffin tops, but I'm just very good at hiding the fact."
The 'Biology' hitmaker admits her weight often yo-yos, particularly as she is currently on hiatus from the group, but refuses to moderate her food intake to stay "unreasonably" thin.
She explained in an interview with heat magazine: "I've put on a bit of weight in the last year as we haven't been touring. I was a 12 when Girls Aloud formed.
"I've definitely become increasingly conscious of my size as time's gone on, especially being in front of the camera so much. But you need to remember that you're a role model for young girls and being skinny-tastic is unreasonable and just doesn't look nice.
"If your body wants a McDonald's, give it one. I live in the country now and it's easier to eat healthily. We have a veg patch - I grow leeks, carrots, strawberries and lettuce."
Sarah - who is in a relationship with DJ Tom Crane - also insisted she eats more when on tour, despite criticism of the group's weight.
She added: "When we tour, people always think we're not eating enough, but actually we're eating more. If I put on weight, it's all muscle and I tend to look thinner."
