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What if the doctor determines that fasting would put a person’s life at risk, but that eating or drinking large amounts is not necessary? In such a case, some halakhic authorities say it is preferable to eat or drink small amounts periodically to minimize the transgression. This translates into drinking 1.3 fluid ounces (40 milliliters) of water every seven minutes or eating approximately an ounce (30 cubic centimeters) of food every seven minutes.
However, if there is any concern that eating and drinking this way may cause any deterioration in someone’s condition, they must eat and drink normally. For example, when a woman is in labor, she should drink freely. If a woman has just given birth and is exhausted, it is better she drink normally (so she will be able to sleep uninterruptedly), rather than drink small quantities over a long period of time (which would force her to stay awake).
Diabetics with unstable conditions also need to be very careful. If there is a concern that eating and drinking minimally may mean they will not eat what they need, they should eat normally. It is also better they pray in the synagogue with a minyan and eat substantial amounts every few hours rather than eat minimal amounts over a long time and be unable to come to the synagogue.
