Although some diet soft drinks contain slightly more sodium than their sugary counterparts, the difference is typically negligible. Most diet sodas are low in sodium, which, according to the Food and Drug Administration's guidelines, means that they contain 140 or fewer milligrams per serving.
One major brand's diet cola contains 35 milligrams of sodium per 12-ounce can, while another major brand's version contains 40 milligrams per can. That's about 5 to 10 milligrams more sodium per can than regular cola. Diet lemon-lime soda may contain more sodium, at 45 milligrams per 8-ounce serving, the same amount as its regular counterpart. Most healthy adults should limit sodium intake to no more than 2,300 milligrams per day, while those with cardiovascular problems should get no more than 1,500 milligrams of sodium each day.