The 27-year-old singer, who recently moved to LA in the hope of landing a role as a judge on the US X Factor, is said to be trying to ditch the cigarettes.
But that, coupled with her loneliness, has led her finding comfort in food instead.
A source told Now! Magazine, 'Cheryl used to smoke when she was stressed. But she's been trying to quit, so she's been eating instead.
'As well as ordering rubbish late into the night, she's also loving Subway sandwiches, which Derek Hough introduced to her last year.
'Normally she's very health conscious, but after a tough day she hits the bad stuff. She knows she's gone up from a size 6 to 8 and put on 5lbs but she's so stressed she has to eat.'