While fasting is a measure of self-restraint, it is not meant to be a measure of self-torture, as an exemption is granted for elderly, infirm and travellers. It was prescribed for pre-Islamic Ummahs’ also, however in a varied form as laid down:
‘’O ye who believe! fasting is prescribed to you as it was prescribed to those before you, that ye may (learn) self-restraint—-(2:183)
Fasting being prescribed for pre-Islamic Ummahs’ does not translate to mean that it was contextually the same or had the same form as was prescribed for Muslims, however it could be said that the principle of self-restraint held true in case of pre-Islamic Ummahs’. The variation was marked in number of days prescribed for fasting, as also in its timing, manner as well. A different regimen was prescribed with a different set of do’s and don’ts.
On who has to take the spiritual exercise and who may not is based on a set of condition, wherein an exemption is granted:
‘’(Fasting) for a fixed number of days, but if anyone of you is ill or on a journey, the prescribed number (should be made up) from days later. For those who can do it (with hardship), is a ransom, the feeding of one that is indigent. But he that will give more, of his own free will,—it is better for him. And it is better for you that ye fast, if only you know’’ (2:184)
Those who can do it with hardship include aged people or specially circumstanced. Some jurists believe that specially circumstanced include women who are expecting or the ones nursing a baby, however some opine that they need to make it up later.