Diet Coke
Diet Coke does not use a modified form of the Coca-Cola recipe, but instead an entirely different formula. The controversial New Coke, introduced in 1985, used a version of the Diet Coke recipe that contained high fructose corn syrup and had a slightly different balance of ingredients. In 2004, Coca-Cola introduced Coca-Cola C2, which it claims tastes much closer to Coca-Cola but contains half the carbohydrates. In 2005, the company introduced Coca-Cola Zero (replaced by "Coca-Cola Zero Sugar" in 2017), a sugar-free variation of regular Coca-Cola.
Diet Pepsi
Though Diet Pepsi is represented worldwide as a low- or no-calorie beverage, the ingredients comprising its makeup vary in some cases by the country of origin. In the US, its ingredients are recorded as "carbonated water, caramel color, aspartame, phosphoric acid, potassium benzoate (preserves freshness), caffeine, citric acid, natural flavor; phenylketonurics: contains phenylalanine". In Canada, the ingredient listing reads: "carbonated water, caramel color, phosphoric acid, aspartame (124 mg/355 ml, contains phenylalanine), sodium benzoate, caffeine, flavor, acesulfame potassium (32 mg/355ml), citric acid, dimethylpolysiloxane". Comparatively in the UK, Diet Pepsi is listed as consisting of "carbonated water, colour (caramel E150d), flavorings (including caffeine), phosphoric acid, sweeteners (aspartame, acesulfame K), acidity regulator (sodium citrate), preservative (sodium benzoate), citric acid, contains a source of phenylalanine".