1. You Will Shorten Your Life
Drinking nothing but Coke or Pepsi for the rest of your life might mean that you're going to have less time to enjoy those sodas than you would otherwise have. It turns out, soda can shorten our lives, and the effects build up over time.
We age because our chromosomes have something called telomeres at the ends, and over time, as the cells replicate, the telomeres get smaller and smaller. Once they are all used up, our cells can no longer replicate, and we die of old age. It happens to everyone, but that doesn't mean you should speed the process up if you don't have to.
A study concluded that a person's telomeres shorten at the same rate for someone who consumes 600 ml of soda a day as it does someone who smokes regularly. Essentially, drinking less than a liter of Coke or Pepsi each day has the same life-shortening impact on your cells as smoking.
This means that drinking soda will age you faster than drinking water does, so if you stopped drinking everything but Coke or Pepsi, you can assume your expiration date has moved up from what it would naturally have been otherwise.