You do not ruin the fast by taking supplements. But you will not get of all the benefits of the water fast. Why throw away those benefits? A lot of research has showed the mental benefits of fasting. There are Christian churches that do it for the mental benefits. This site on Fasting that has quotes by 18 MDs. Three of them are psychiatrists. It tells about the mental benefits which are as profound as the mental benefits. Actually it is the best way to heal mental problems. http://www.phifoundation.org/fast.html