liver and kidney function tests should reveal any indications of the onset of disease and their stage of development, so if function is too poor, then dietary advice pre-fast would be advisable to improve their function before the commencement of a fast proper.
This does not necessarily mean being forced into Allopathic treatment, but targeted nutrition such as carrot juicing
to cleanse and heal the liver and lighten the load on the kidneys. These organs are also given an added rest on a juice-feast, allowing them to heal more before the intense detox of a water-only-fast and the overworking of both organs.
Much would depend on the levels of toxemia as to whether to begin a water-only-fast would be appropriate or not in this state. The best method in determining this is to drink pure water according to thirst for only 48 hours; during time if one experiences headaches, general malaise, weakness, bad breath, a coated tongue, and so on, then toxemia is high; but on the other hand, if the experience is one of elation, growing strength, mental clarity and none of the above, then toxemic levels are low or non-existent, and precautions for the Liver and kidney can be ignored.