Often what is used to 'replace' salt is potassium chloride, which would be dangerous for those with kidney issues. I take a popular medication for high blood pressure control, lisinopril, which can interfere with potassium elimination by the kidneys so I have to be careful with it myself. I haven't needed to avoid potassium-rich foods which contain it naturally (periodic testing of potassium serum levels confirms this), but artificial supplementation with potassium chloride can be especially dangerous; V-8 vegetable juice is an excellent example: it's processed so heavily during production that nutrient are destroyed, so supplements are added, including enough potassium chloride to bring potassium levels to > 700mg in a 6 oz serving, so it's best avoided.