Re: ~ 100 oz. of soda per day: Long-term effects?
I know a few people who have been lucky and drink 10+ cans of soda a day and haven't had ANY problems, but not everybody is nearly this lucky. Unfortunately there is no easy answer to your question b/c it really depends on your body.
Some people get cavities very easily even with good teeth cleaning and a good diet. Other people can eat lots of candy and sodas and never have a cavity. I understand that it's not easy to make a big change in your soda habits, so I'd say it's best to make sure to keep regular dentist appointments to keep an eye on your teeth. A lot of sugar isn't good for them, so make sure to get regular cleanings and x-rays.
I am a diet soda drinker, but I try to limit myself to 1-2 drinks a day. Studies do show that some people crave more sweets after having diet sodas, but this never happens to me. I can actually be craving something sweet, have a diet soda, and feel happy and not want sweets for the rest of the day. It just depends on your body's own reaction. You may want to experiment some. Try swapping some of those regular sodas for diet and see how you handle it. You can cut out a lot of the extra calories and sugar that way if it works for you.
I've also tried to swap some sodas for a cup or morning coffee or even green ta. I just need that extra boost from caffeine. They have antioxidants, plus I put some skim milk in my coffee and get some calcium.
Be sure that you are getting enough water as well! Too much soda can cause urinary problems and can cause dehydration. Be sure to balance it out. I do know some people who had problems with their urine from only drinking sodas all day.
Studies have also shown that too much soda (diet or regular) may be linked to lower bone density. I'm not too sure how far this study goes, so be sure to have plenty of calcium to keep your bones healthy. The article I read about it said that this was true for any caramel-colored sodas, not the clear ones or other colors.
If anything, I'd suggest trying to slightly lower the amount of soda you have. I know many people who drank lots of it throughout the years and are fine, but there are always those risks of tooth decay, diabetes, obesity, etc. I find that if you are a very active person, you can get away with more sugar/calories, but the typical person probably can not.