Is a chronically ill cancer patient required to fast if a non-Muslim doctor advises against it, even if the patient feels capable of fasting?

If a Muslim is unable to consult a Muslim doctor, it is permissible for him to accept the opinion of a non-Muslim doctor if he is truthful and trustworthy, even if he is not a Muslim. This is based on personal experience or the information provided by a skilled doctor, for what matters is truthfulness, not justice. This is restricted to cases where a knowledgeable Muslim doctor is not available, unless the non-Muslim doctor is more knowledgeable than him. This ruling applies to matters such as tayammum (dry ablution) and fasting.