Foods with a lot of simple carbs like White bread, Doughnut, Corn flakes, Cooked spaghetti, Raisins, etc. Have been proven to increase the blood sugar level your body naturally produces. This ends up in the production of more insulin (an oil producing hormone). The result you get are clogged pores, leading to pimples.
Conclusion: Aside taking in a balanced diet, you can also cut down excess intake of simple carbs.