Halakhah su Deuteronomio 4:15

The question of whether smoking is prohibited not only on Yom Tov but at all times hinges upon the general halachic requirement that we refrain from dangerous and unhealthy activities. The source for this requirement is Devarim 4:15, where we are instructed, “V’nishmartem me’od l’nafshoteichem,” “You shall guard your souls exceedingly carefully.”⁵For a full discussion of this matter, see the essay written by Dr. Shalom Buchbinder and Dr. James DiPoce in The Journal of Halacha and Contemporary Society 42:70-99. The Rambam seems to divide this requirement into two different categories. He lists (Hilchot Dei’ot 4:1) certain foods and activities that, because they weaken the body, one needs (“tzarich”) to avoid, but also mentions (Hilchot Rotzeiach Ushmirat Nefesh 11:5) numerous dangerous activities that Chazal outright prohibited. The activities listed in Hilchot Rotzeiach Ushmirat Nefesh appear to be strictly forbidden, while those in Hilchot Dei’ot seem to be discouraged, but not technically forbidden. Rav Waldenberg (Teshuvot Tzitz Eliezer 15:39) understands that this is because the former are far more dangerous than the latter. Thus, while it is technically prohibited to drink from water in which a snake may have placed its venom, it is not outright prohibited to overindulge in fattening foods.

Because the maintenance of a complete and healthy body is a G-dly path—since it is impossible to understand or apprehend any knowledge of the Creator when one is sick—therefore you must keep away from things that damage the body, and develop habits that improve the body and heal it. Similarly, it is said: “You shall guard yourselves very well.”¹Devarim 4:15.