Kudos to Lady Gaga - if she really means it. Don't put any money on her feeling this way for long. In fact she is already saying she is dieting for her new tour. So don't be surprised when next week we may see her on a miracle diet in which she will have lost 20 pounds in two weeks. She may just go back to the 5 Factor Diet (see video).
In any case in an interview with radio host Elvis Duran, Lady Gaga explained that, despite people wondering about why she may have gained weight (i.e. is she pregnant?) she admitted that being a home body and eating home-cooked Italian meals means extra weight.
Lady Gaga, 26, has gained about 25 pounds (from a news story) and blames her dad who opened a restaurant. “My father opened a restaurant. It’s so amazing . . . it’s so freaking delicious, but I’m telling you I gain five pounds every time I go in there,” she told Duran, “So my dad wants me to eat at the restaurant, and I’m, like, I've got to go where I can drink green juice.” source
Gaga also loves pizza when she is on tour so she cannot just blame her dad. It seems that pasta and "Italian" food are her comfort foods of choice and she may just binge on fattening albeit yummy items.
In addition she is small and loves to eat so if she slips on her work outs the weight piles on quickly.