Shaykh Abdul-Muhsin Al-Abbaad was asked:

Question:

“Is a person sinful if they leave off a diet [i.e. take on a particular diet] until he is harmed by that? [by taking on this diet]”

Answer:

“It is not for a person to do something that leads to harm or increases his harm. As it is said, dieting is the best of cures, such that a person takes a protection in the form of a diet. As it is well-known, the occurrence of harm is by the permission of Allah. There can be harm and there may not be harm if Allah wills. However, Allah decreed means and He has made some of these means and things a cause for the increase in sickness. So the least thing [that can be said] is that even though he is not sinning, he should not expose himself to what causes him harm”. End translation. [Sharh Tirmidhi no. 222]

Translated by

Faisal Ibn Abdul Qaadir Ibn Hassan
Abu Sulayman