Alexei Vella Junk-food giant PepsiCo is preparing to make the biggest change to its Diet Pepsi brand in three decades, Bloomberg News reports: it's nixing the controversial low-calorie sweetener aspartame. In its place, Diet Pepsi will get its sweet jolt from a mix of sucralose and acesulfame potassium. The apparent reason for the shake-up: Diet Pepsi sales plunged 5.2 percent last year, Bloomberg noted.