A significant factor that determines if a crystal will develop into a kidney stone is the saturation of the urine with stone-forming salts. From my understanding, supersaturation leads to precipitates which result in stones. Undersaturation does not lead to stones. So my question is what determines super/undersaturation from a dietary perspective? Does increased water intake help dilute the concentration of the crystals (eg. calcium oxalate, calcium phosphate), thus preventing the formation of stones?
If you have kidney stones or you are at increased risk of developing them, ask a doctor if your urine is super- or under-saturated with any substance, such as calcium, oxalate, uric acid, cystine or citrate; this is a crucial info that can tell if any diet can help. Explanation at-a-glance: Eating, Diet, & Nutrition for Kidney Stones by NIDDK.
Evidence about dietary measures that may help prevent CALCIUM OXALATE stones:
1. High water intake
Other fluids, such as tea, coffee, wine and beer might also help, but milk, soda and fruit juices might not, according to one 2015 systematic review of studies.
2. High citrus/citrates intake
Potassium citrate supplements and possibly (?) citrus juices (PubMed 2017, 2016), which alkalize the urine, can decrease the risk of stones, but this 2015 Cochrane review does not strongly support this evidence. Additionally, potassium citrate supplements may have a lot of side effects.
3. High dietary calcium intake
Surprisingly, high intake of calcium from foods was associated with lower risk of kidney stones in several big observational studies. On the other hand, calcium supplements may increase the risk. According to Linus Pauling Institute, calcium may inhibit the absorption of oxalate in the intestine and thus its accumulation in the urine.
4. Low sodium (salt) intake
Low sodium intake (< 3.8 g salt/day) decreases calcium excretion in the kidneys and thus the risk of stones (Linus Pauling Institute).
5. Low oxalate intake
For URATE stones, apart from above measures, diet low in animal proteins can help (PubMed, 2004).