Sugar-sweetened drinks are associated with worse health outcomes across a very large body of observational research. Caffeine is genuinely contested — it increases urine output, which helps, while some analyses suggest it nudges stone risk indices the other way. And the near-universal instruction to drink more water rests on a thinner trial base than its confidence implies.
Sugar-sweetened drinks
An umbrella review published in 2024 pooled 47 meta-analyses covering more than 22 million people. Across those analyses, 79% found direct associations between higher sugar-sweetened beverage consumption and higher risk of an adverse health outcome.
That is a strong and consistent signal about sugary drinks generally. Be precise about what it is, though: these are observational studies. They show that people who drink more of these things have worse outcomes — not, on their own, that the drink caused it. People who drink a lot of soda differ from people who do not in many other ways.
For kidney stones specifically the evidence is of that same observational kind, and it points the same direction.
Caffeine is not the same question
This is where most coverage goes wrong, because soda, coffee, tea, and energy drinks are lumped together when they differ in what they contain.
A 2018 review examined caffeine specifically and found the picture genuinely contradictory:
- Caffeine is a diuretic, so it increases urine output — which is the direction you want, since diluted urine is less likely to form crystals
- But it may slightly raise stone risk indices through other mechanisms
- Meanwhile three large cohort studies suggested a protective association
So "caffeine is bad for stones" and "coffee prevents stones" are both overstatements of a literature that has not settled. If someone tells you confidently either way, they are ahead of the evidence.
The thing the fluid literature admits about itself
Everyone with a kidney stone is told to drink more water. Keeping urine volume above about two litres a day has been the standard prescription for decades.
Here is what a 2017 review of that literature says plainly: the recommendation rests on only one randomised controlled trial. The rest of the support comes from epidemiological studies and basic science, which point the same way but are not the same thing as trial evidence.
That does not make it wrong. Increasing urine volume has the most mechanistic sense behind it of any intervention in stone prevention, the epidemiology is consistent, and the same review notes it is still the cornerstone. But the confidence with which it is delivered outruns the evidence base behind it, and you are entitled to know that.
It also means the more interesting open question is not whether to drink more, but what to drink — where the evidence is thinner still.
What none of this settles
Not one study here tracked what happens if a specific person stops drinking a specific drink. They measured populations, or urine chemistry, or both.
What your own fluid intake is doing to your urine is measurable, precisely, on a 24-hour urine collection — the volume figure answers in one number what no amount of reading can. That is the conversation worth having.