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Some critics point to lack of essential nutrients in this fast, citing a deficiency of protein, vitamins, and minerals.[5]
As a result of these deficiencies, individuals on the diet may experience dizziness, delirium, and fainting in the short term, with possible damage to the body occurring in longer-term applications.[5] Dr. Joel Fuhrman attributes these effects to detoxification, which he says passes after the toxins are eliminated.[6]
Many authors assert the benefits of fasting are related to its lack of nutrients, particularly macronutrients.[6][7][8][9]
Dr. Ed Zimney has asserted that, while toxins (such as mercury from the ingestion of fish) do accumulate over time, lemon juice and maple syrup could "not in any possible way eliminate any of these toxins." [10].
People with intestinal conditions such as Irritable Bowel Syndrome may experience added discomfort while on the cleanse. However note that this is in fact one of the treated conditions of the fast.[citation needed]
There is a risk that the saltwater "flush" may remove both beneficial and harmful bacteria from the body[5]. A no-food diet may cause the gut to stop passing food, resulting in constipation, or may make the consumption of food immediately after the fast painful. These are the important reasons to follow the fasts' instructions correctly.
I highly doubt the problems are due to "detoxification," but more the body reacting negatively to the sudden loss of expected nutrients and solid matter intake. Forced metabolism changes aren't going to happen painlessly.