Giving up sugary carbonated drinks is one of the few dietary changes with a clean before-and-after, which is exactly why it attracts exaggerated claims in both directions. It is worth separating what follows reliably from what depends entirely on what replaces it.
The calorie arithmetic is the least interesting part, and the most dependable
A daily can carries roughly 140 calories with no satiety to show for it — liquid sugar does not blunt appetite the way the same calories in food would. Remove it and replace it with water and the deficit is real. Replace it with juice or a sweetened coffee and there may be no deficit at all. Most disappointed people are in the second group.
Dental benefit is the best-established outcome and the least discussed
Both the sugar and the acidity matter for enamel, and the effect depends on how often the exposure happens rather than the total volume. Sipping one drink across an afternoon is harder on teeth than drinking it in ten minutes. Dentists have been consistent on this for decades.
Diet versions are a different question, not a settled one
Swapping to a zero-calorie version removes the sugar and, in trials, usually produces modest weight change compared with continuing. Whether long-term use of non-sugar sweeteners has other effects is still argued over, and anyone claiming the matter is closed is overstating in one direction or the other.
The headache in the first week is usually caffeine
Many colas carry a meaningful caffeine dose. Stopping abruptly produces the ordinary withdrawal headache, which resolves in a few days and is often misattributed to "detox". Tapering avoids most of it.
Carbonation itself is largely a red herring
Plain sparkling water is not the problem in a sugary drink; the sugar and the acid are. For people who mainly miss the fizz, unsweetened sparkling water is a genuinely close substitute, and one of the few swaps that tends to stick.
How to judge the claims you will read
Ask what the drink was replaced with, over how long, and whether the outcome measured was weight, a blood marker or a feeling. Most of the disagreement in this topic is people answering three different questions with one number.
If you are pregnant, manage a medical condition, or take medication affected by fluid or caffeine intake, check with your doctor before making a large change.