Scientific study linking acne with low glycemic load: http://ajcn.nutrition.org/content/86/1/107.full
Commonly tout as healthy food but has high glycemic index(avoid it, if u are acne-prone): rice, noodles, potatoes, watermelon, bread, crons, carrot, banana, raisin plus all sugary stuffs.
Glycemic index food list: http://www.health.harvard.edu/newsweek/Glycemic_index_and_glycemic_load_for_100_foods.htm
Food with glycemic index rapidly increase your blood sugar level after you eat it, which somehow cause acne.