These halakhot are generally addressed to doctors, who must determine, based on their medical expertise and experience, when there is concern of endangerment, and when there is not. The problem is that many doctors, whether out of excessive caution or lack of respect for the mitzva of fasting on Yom Kippur, always tell anyone who is sick to eat and drink. Some doctors mistakenly believe that if they tell a sick person to eat or drink only minimal quantities (le-shi’urim), there is no prohibition. In truth, the Torah forbids eating and drinking even in small quantities. Only in the case of a patient deemed dangerously ill enough to eat and drink is it preferable, when possible, to eat and drink le-shi’urim (as explained in the next section).
Therefore, questions about fasting must be posed to a God-fearing doctor. This does not mean asking a doctor who wears a particular type of head-covering; rather, the doctor must be moral and ethical, and reach decisions responsibly, factoring in both the sanctity of the day and the sanctity of human life. Patients have the responsibility to approach the doctor out of reverence for God, for if they pressure the doctor to permit them to eat and drink, they are putting the doctor in a very difficult position: He already bears great responsibility, and they are now making it difficult for him to determine whether they are really at risk, or if they simply want to get out of fasting even though there is no risk to life at all. A critical amount of the doctor’s information comes from patient input, so when a patient presses for a dispensation, the doctor may conclude that he is in bad shape and permit him to eat and drink minimal quantities, whereas if the patient had reported honestly, it may have clarified that the situation is not life-threatening at all. In cases of misrepresentation, responsibility for the erroneous ruling lies primarily with the patient.
A God-fearing doctor who is uncertain as to whether a person must fast should consider: “What would I do on Yom Kippur were I to find out that this person was fasting? Would I be willing to violate Yom Kippur by driving for ten minutes to instruct the patient to eat and drink, thus possibly saving his life?” If the answer is yes, it indicates that the doctor believes that there is a true danger to life, and he should instruct the patient beforehand to eat and drink on Yom Kippur. If, however, despite the responsibility he feels for his patient’s well-being, he would not be willing to drive on Yom Kippur for him, it indicates that the doctor believes there is no real danger to life, and he should instruct the patient to fast. This suggestion is effective for the average doctor, who is not lazy but also prefers not to rush from one patient to another.
If a patient mistakenly consulted a doctor who is not God-fearing, and the doctor instructed him to eat and drink, then the patient must make every effort to ask a God-fearing doctor before Yom Kippur. If the patient did not ask, and Yom Kippur has begun, he should eat and drink. Although we are uncertain whether the doctor answered in accordance with halakha, it nevertheless remains a case of uncertainty (safek) in which life is at stake. We therefore are stringent and instruct the patient to eat and drink.
It is important to know that even though these halakhic decisions are in the hands of doctors, if a patient thinks that his life may be in danger, and that eating and drinking can save him, then even if the doctors disagree, he should eat and drink. This is because sometimes a person can sense the gravity of his condition more than doctors can, as it is written, “The heart alone knows its bitterness (Mishlei 14:10)” (Yoma 83a; SA 618:1). However, if the patient says he must eat, and the doctor thinks that eating would endanger his life, we pay heed to the doctor (AHS 618:5-6; SSK 39:4).
Accordingly, if conventional medicine dictates that one should fast, while alternative practitioners say he should eat, we disregard the alternative practitioners, and the patient must fast; conventional doctors are considered more expert because they rely on comprehensive research, and they also constitute a majority. However, if the patient is convinced that the alternative practitioner is correct, he may eat. (See Rema 618:4.)
In Peninei Halakha: Shabbat 27:2, I explain that we listen to the patient over the doctors as long as there is some logic to the patient’s claims. However, if the disease and its treatment are known, but the patient demands treatment that the doctors deem ineffective and that entails Shabbat desecration by someone other than the patient, we listen to the doctors (BHL 328:10 s.v. “ve-rofeh”). Likewise, if the patient is known to be excessively fearful, and the attending caregiver is certain that he is not in danger, the patient should not eat. If, despite the doctor’s view, and despite being aware of his own tendency to worry excessively, he remains sure that he must eat, he may act accordingly. (See Tzitz Eliezer 8:15:7:25, which states that sometimes it is permissible for the patient to desecrate Shabbat on his own behalf, even when it would be forbidden for a doctor.)