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Diet plays an important role in the management of kidney disease.
The diet your physician will ask you to follow will be based upon your level of kidney function, your body size, and any other medical conditions you may have. Your diet may be helpful in delaying the need for dialysis.
Mineral water does contain variable amounts of sodium and potassium in it. Hence consuming it might increase the solute load on the kidney. Typical potassium content in bottled water is less than 5 mg/l, but some can have as much as 50 mg/L. Sodium in bottled water ranges from 10 mg/l in most bottled waters to 1,200 mg/L. Hence it has been advised by your doctors to avoid mineral water.
Raw vegetables and fruits contain more potassium. The kidneys are responsible for helping to keep the correct amount of potassium in your body. It can be very dangerous if your potassium level is too high. Too much potassium can make your hear beat irregularly or even stop without warning. Hence you need to avoid foods that contain too much of potassium (Including - fruits, vegetables, banana, broccoli, tomatoes, prunes, mushrooms, raisins, dried fruits, mustard, beet, apricots, etc).
In case of any doubt, you may consult with your treating physician who can advice you accordingly.