I agree with Mike's logic (if not with all of his tone) but its right - ending ketosis is not only unhealthy (its muscle wasting) but its also more difficult to maintain the fast afterwards.
However there is a much more serious reason you shouldn't do it which is that if you eat carbohydrates while depleted of phosphorus, magnisum, and potassium (which are contained in fruit juice, fruit and vegetables - which is how most fasters who know how to end their fast avoid it) you risk potentially fatal complications called 'refeeding syndrome.'