OK several things here.
Non-diet soft drinks are bad for your health for several reasons.
High caloric content/low satiety index - You can drink a lot of calories and still have room for more, meaning that soft drinks contribute to obesity. Nutritionists will often recommend cutting soft drinks from your diet as the first thing you should do to lose weight, as it is a huge source of non nutritive calories. 1 soda per day = 150 calories per day = 4500 calories per month = 54000 calories per year = about 15 pounds of fat per year.
Highly bioavailable sugar (eg high glycemic index) contributes to insulin resistance more readily than low glycemic index sugar. Granted, total sugar consumption is far more important than glycemic index. This bit is more speculative than the rest. Here is a cite, which is far from conclusive, in my opinion.
pH and chelating agents damage teeth - This one is pretty conclusive. There are two big ways soft drinks can go bad. Bacterial growth, and oxidation of volatile oil flavor compounds. Calcium is a potent catalyst for oxidation reactions. To prevent premature oxidation, manufacturers put citric and phosphoric acid into their soft drinks to chelate the calcium and prevent it from catalyzing the oxidation of volatile oils. The problem here is that your teeth have a lot of calcium in them as well, and the citric acid chelates that calcium just as well as it did in the can. The reason why fluoride is good for your teeth is that it forms stronger bonds than calcium does and resists this kind of decay. pH also acts in the same way.
Your stomach is meant to be at a low pH. Your mouth isn’t. Conditions which cause chronic vomiting, such as bulimia, also cause tooth decay by means of repeatedly exposing teeth to low pH. It doesn’t take a leap of faith to see how exposing your teeth to soft drinks might cause tooth decay over long periods of time.
Here is a fun experiment. Take a tooth and put it in a glass of coca cola for one week. At the end of the week, it will be completely dissolved. Here is a video of a tooth spending one day in coke:
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Artificial sweeteners are bad - FALSE (with some exceptions). There are a lot of sweeteners which have no media hype surrounding their negative health consequences. A short list would include acesulfame potassium, sucralose, and various sugar-alcohols. The big controversy regarding artificial sweeteners revolves around aspartame, which is a dipeptide consisting of aspartic acid and phenylalanine. Aspartic acid is an excitatory neurotransmitter which acts in a similar fashion as glutamate in the ventral spinal cord. High doses of aspartic acid can cause anxiety, headache, nausea, and vision problems. The problem is… is that you need a LOT of aspartic acid to cause these side effects. A can of diet coke contains about 130mg of aspartame. Only about 40% of that is aspartic acid, so there is roughly 50mg of aspartic acid per can of coke.
HOLY SHIT, you might say. Each can has 50mg of aspartic acid? Big freaking deal. 50 grams of chicken has around 1000mg of aspartic acid. It is a common amino acid and its presence in soft drinks is not terribly alarming. You would drown in coca cola before you kill yourself from the aspartic acid content. The LD50 of aspartic acid in rats is 5000mg/kg. Assuming that number translates to humans, it would take .9 pounds of aspartic acid, or roughly 8000 cans of soda consumed in one sitting, to kill 50% of the humans exposed. If you don’t feel like drinking that much soda, you could also do just as well by eating 45 pounds of chicken in one sitting (digesting it perfectly, mind you).
Whats the take home message? Soft drinks aren’t good for you. Regular soft drinks contribute to obesity and all soft drinks damage your teeth over time. That being said, soft drinks aren’t made of rat poison either and the hype about the dangers of aspartame is just bullshit. So go ahead and enjoy your soft drinks, but enjoy them sparingly.
Side notes:
Saccharin and cyclamate have been shown to cause bladder cancer in rats. Some problems with that finding is that the concentrations you need to cause bladder are much higher than one would reasonably expect in real life, and that rats are predisposed to bladder cancer to begin with. Even still, I personally avoid these sweeteners as there are good substitutes available.
Here is what coca-cola does to polyethylene terepthalate utensils:
