Declining sales of both regular and diet Coca Cola have caused the company to launch a series of print ads that will defend the artificial sweetener aspartame, also known as NutraSweet. The ads begin Wednesday in USA Today in the Atlanta area, followed by the Atlanta Journal Constitution on Thursday and the Chicago Tribune next week. The ad says that diet drinks can help people manage their weight and stresses the scientific evidence showing the safety of aspartame. It is a second phase of a campaign Coca-Cola launched in January to defend regular Coke from obesity concerns. But there has been declining sales of the diet drinks as well. Last year, for example, sales volume for Coke fell 1 per cent, while Diet Coke fell 3 per cent. Pepsi fell 3.4 per cent, while Diet Pepsi fell 6.2 per cent.