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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?

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    Welcome to MedicalSciences.SE! Please take the tour and read the help center. For reasons mentioned in this post and in How to Ask, we require prior research information when asking questions. Please help us to help you and edit your question to provide more information on what you have read on this subject, particularly when you say you read that supersaturation leads to precipitates which result in stones. – Chris Rogers Dec 27 '18 at 23:42
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    I am voting to close this question as there has been no indication of prior research despite the fact that there are requests for it – Chris Rogers Dec 29 '18 at 12:19
  • Obviously, the OP has done some research, but in the case of kidney stones, translating the dietary changes into urine concentration changes and stone formation risk is more tricky than it seems. – Jan Dec 29 '18 at 12:27
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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

According to several studies, drinking 3-4 liters of water per day (to produce at least 2 liters of urine/day) can decrease the risk of stones (PubMed, 1999, 2016).

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.

It is not clear if hard water (high in Ca and/or Mg) is a risk factor for kidney stones (PubMed, 2018, 2002).

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

Diet low in oxalates can reduce the risk of stones if your urine has too much oxalate (PubMed, 2016).

For URATE stones, apart from above measures, diet low in animal proteins can help (PubMed, 2004).

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