Preventing kidney stones starts with your urine volume, and the rest is secondary. A systematic review and meta-analysis found that high fluid intake lowers the risk of both first and recurrent kidney stones (PMID 26022722). In athletes that is harder than it sounds, because every session costs you fluid you never count.
Drinking two litres and passing two litres are not the same thing. That gap is exactly where it goes wrong.
Why are athletes at higher risk of kidney stones?
Four factors stack: significant fluid loss through sweat, a high protein intake, plenty of oxalate from vegetables and nuts, and heat or sauna on top of your training volume. Each alone is manageable. All four together concentrate your urine, and concentrated urine is where crystals form.
Picture the classic physique lifter who drinks 3 litres a day. That sounds like a lot, but he sweats one and a half out in the gym and another half in the sauna.
On top of that he eats 220 grams of protein and drinks a daily smoothie with a large handful of spinach. Spinach is among the richest oxalate sources there is.
The Nierstichting describes kidney stones as crystals that form when substances in your urine become too concentrated. Diluting is therefore the most direct lever.
How much should you drink to prevent kidney stones?
The target is not a number of litres you drink but a urine volume of roughly 2 to 2.5 litres per day. That is the measure the prevention studies keep returning to. As an athlete that almost always means drinking more than a non-athlete with the same target.
A systematic review in Annals of Internal Medicine lists increased water intake as a measure for calcium oxalate and calcium phosphate stones (PMID 41871357).
In practice you do not need a measuring jug. The colour of your urine through the day tells you plenty, and I work that out in dark urine after training.
Should you eat less protein to protect your kidneys?
Not if your kidneys are healthy. A meta-analysis of 28 trials with 1,358 healthy adults found no adverse effect of higher protein intake on kidney function (PMID 30383278). What protein does do is raise the acid load of your urine, which can work against you if you already form stones.
The distinction matters. Protein causes no damage in a healthy kidney, but it can shift the chemical climate in a stone former.
If you have never met a stone, your protein intake is not your biggest worry. Your fluid intake is. More on that in protein intake and your kidneys.
What works and what is nonsense?
Diluting works, cutting salt helps with calcium stones, and cutting dietary calcium does not. That last one surprises many people. Calcium in your meal binds oxalate in your gut, so less of it reaches your urine.
| Measure | What it does | Practical for an athlete |
|---|---|---|
| Urine volume 2 to 2.5 litres per day | Dilutes the substances that crystallise | Add your sweat losses, not just what you drink |
| Less salt | Lowers calcium excretion in urine | Watch ready meals and electrolyte drinks |
| Keep calcium with the meal | Binds oxalate in your gut | Quark or milk with your spinach rather than after it |
| Spread out oxalate bombs | Prevents peaks in your urine | Not the same spinach smoothie every single day |
| Lemon or lime in water | Citrate inhibits crystal formation | Easiest addition to your bottle |
| Cutting dietary calcium | Backfires, more oxalate reaches your urine | Do not do this without medical advice |
That last row is there deliberately. It is the advice people most often give themselves and it works in the wrong direction.
Which blood values belong here?
Uric acid, calcium, creatinine and eGFR together give a usable picture. Uric acid matters because some stones are made of urate, and because a meat-heavy diet raises that value. With repeated stones, urine analysis belongs in the workup too.
Our 360 Health test includes uric acid, creatinine and eGFR.
How to read those values as an athlete, including what your muscle mass does to them, sits in kidney values in athletes.
If you have already had a stone, find out what it was made of. Prevention differs by stone type, and without that detail you are guessing. In that situation I would sit down with a GP before adjusting my diet.
References
- Cheungpasitporn W, et al. Treatment effect, adherence, and safety of high fluid intake for the prevention of incident and recurrent kidney stones. J Nephrol. 2016. PMID 26022722.
- Prevention of Recurrent Nephrolithiasis in Adults and Children: A Systematic Review. Ann Intern Med. 2026. PMID 41871357.
- Devries MC, et al. Changes in Kidney Function Do Not Differ between Healthy Adults Consuming Higher- Compared with Lower- or Normal-Protein Diets. J Nutr. 2018. PMID 30383278.
- Nierstichting. Symptoms and investigation in kidney problems. Accessed 2026.
Disclaimer
Every blood test result includes a professional assessment from a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. A blood test is a tool to walk into the conversation with your GP better informed, not a diagnosis in itself. Discuss any abnormal value with your GP.
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