It's not uncommon if you drink a lot of soft drink actually. When I used to drink a can or two of pepsi a day water did give me heart burn. I used to be on proton pump inhibitors for my heartburn (now since off them as I got back down to human size, knocked off drinking so much soft drink and learned that apple cider vinegar helps clear up heart burn immediately and get stomach acid production back to normal). Legitimately it's because your stomach acid production is fucked from the soda. Soft drink is acidic which means when you drink it a lot your stomach doesn't produce as much acid as it should. But it is not the same kind of acid your stomach produces, it is much weaker so it's also unhelpful in digesting food. Since you're not producing enough stomach acid your stomach has to crunch up the contents itself and churns harder than it should be. With added weight p  3ffa  utting pressure on the stomach, plus the gases from the soft drink, the valve that stops stomach acid from getting into the oesophagus becomes leaky from the pressure build up (also if your stomach pH is not low enough bacteria can thrive in there, chewing up carbs and excreting ammonia that makes the problem worse and also gases that increase the pressure on the valve). Water being slightly alkaline causes your stomach to produce more acid to counteract, but since it's still not enough, (if ypu have chronic heartburn), the stomach churns just as hard, but now more stomach acid is getting up into the oesophagus. I did a lot of research on how to fix my stomach acid production. My doctor told me I was producing too much acid so put me on proton pump inhibitors which limit stomach acid production. In reality my stomach wasn't producing enough. The pills worked because my stomach wasn't producing enough acid to have it get to my oesophagus... in reality the pills were making the problem worse.  Fortunately you can reverse this easily and retrain your body to start producing stomach acid normally, which is what I did using HCL pills. I later found out that is also kind of dangerous, if a pill gets stuck and dissolves it can do some serious damage to your throat. BUT there is a much less expensive and simpler way to fix stomach acid production. Drinking apple cider vinegar when you get heart burn will not only immediately stop your stomach from churning so hard, but it also helps to bring stomach acid production levels back to normal over time, in much the same way HCL pills did for me. Now I can drink water with no issues. I have not had heartburn for years despite used to getting it chronically every day. I only get heartburn these days if I eat too much. I drink soft drink very rarely now. A can every so often isn't going to be a problem, but drinking a can or more every day is going to cause some issues for your body no matter what size you are.  Hope that explains that mystery for ya 😉