I hope I'm wrong. I just remember knowing exactly what he meant when Chris Voigt said the docs had to test his kidneys before he embarked on his potato fast.
I don't know what the policy is for posting links, but just google the following words and you will get hits on what I am talking about. The potato hack is not for anyone with kidney problems.
chris voigt potassium kidneys
Also, if you google salt substitutes for kidney disease, you will see that kidney patients are to beware because these contain a lot of potassium. My husband was supposed to avoid salt because of heart problems, so I bought salt substitute. I had no idea it was dangerous because of kidney problems. No one told him until he landed in the hospital - it was the early days of his kidneys going down hill. He had gained over 10 pounds in a few days. His diuretics for his heart problems were kicking his kidneys. Hydroclorathiazide and Zaroxalyn are particularly harsh, but a lot of people are on diuretics for high blood pressure. Also, potassium-sparing diuretics like spironolactone (popular, I believe) or amiloride actually make the body hang onto potassium, so eating an unusually high potassium diet is not a good thing with these drugs. It's called hyperkalemia. There are other causes of hyperkalemia, this is just the one I am familiar with. Other drugs or conditions can do it, I see.
I might be paranoid because of personal experience, but a person is not supposed to gain more than 10 pounds within a few days without going to get it checked out urgently.