Some have phosphoric acid, which leaches calcium from your bones. Not all soft drinks have phosphoric acid:
In a survey designed to measure the amount of phosphoric acid in twenty different soft drinks, the following were found to contain the highest amounts: Tab, Coke, Diet Coke, caffeine-free Coke, and Mr. Pibb. The formulas may have been changed for the better since this survey was conducted. . . . Pepsi Free, Diet Pepsi Free, Like Cola, 7-Up, and Mountain Dew had no phosphoric acid.
Female Fertility and the Body-Fat Connection (2004) by Rose Frisch, an excellent book, tells about a 25-year-old college tennis player nicknamed Miss Tab because she drank 8-10 bottles of Tab a day.
When her bone mass was measured, her tennis arm was normal for a 25-year-old woman (it should have been a greater mass from the exercise) and her other arm had the bone mass of a 70-year-old woman.
I started drinking Diet Coke a week ago. Oops. I will switch to Diet Pepsi. Eventually I will learn the Chinese for phosphoric acid.
Maybe it’s different in China, but Diet Pepsi has phosphoric acid here in North America. Maybe you meant you were going to switch to those other Pepsi products (Pepsi Free or Diet Pepsi Free) that I haven’t seen myself?
https://www.pepsiproductfacts.com/infobyproduct.php?brand_fam_id=1051&brand_id=1000&product=Diet%20Pepsi&prod_type=1026