Diet sodas are composed primarily of the same ingredients as their regular counterparts, with the exception of sweeteners. While regular sodas use corn syrup or cane sugar, diet sodas use artificial sweeteners such as aspartame, Stevia and sucralose. Other minor differences include which preservatives are used.
Aspartame, Stevia and other sugar substitutes have long been considered health risks, with claims that they cause various forms of cancer. Some medical resources cite these artificial sweeteners as FDA-approved for those suffering from diabetes, since they do not raise blood sugar levels.
Aspartame has undergone scrutiny in many studies, and health scares have surrounded the substance. Some studies say that aspartame is safe in small amounts, while others suggest it could be linked to certain forms of cancer. Aspartame is the sugar substitute used in a few major diet soda brands, though some brands have recently removed it.
Stevia has had fewer health scares but is less common in diet sodas. Stevia is only safe once processed and not in its raw form. Ultimately, regular soda has nearly identical ingredients to diet soda, with the main differences being how many calories the sweetener contains and the variations in flavoring from brand to brand.