Tzitz Eliezer - Nutritional Supplements On Erev Yom Kippur?
The Sdei Chemed says that since the Mitzva of fasting on Yom Kippur is because the Torah says "V'Inisem Es Nafshoseichem", you must afflict yourself, therefore it is not proper to ingest pills or do any segulos on Erev Yom Kippur that will minimize the natural effects of the Ta'anis.
The Chelkas Yaakov (2:58) and Tzitz Eliezer (7:32) argue and both hold that it is permissible to eat whatever you want on Erev Yom Kippur, as we see the Torah even gives us a Mitzva to eat on that day. The Mitzva of V'Inisem is fulfilled by not eating anything on Yom Kippur.
The Piskei Tshuvos (611:1:2) says that although it seems that the Shela HaKadosh was Machmir by other Taaneisim, he was not referring to Yom Kippur, which is a Yom Tov and is not a day of aveilus. Important Note: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. One should learn the tshuva to verify the accuracy of our interpretation. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.