How can one balance the necessity of eating to gain weight with avoiding gluttony, which is blameworthy in Islamic law, especially given the feeling of quick satiety and sluggishness in performing acts of worship resulting from overeating?

If you do not fear harm from excessive thinness, adhere to the Prophet’s (peace be upon him) recommendation regarding eating, which is not to eat more than one-third, as this is more beneficial for the body and the religion. It is permissible to eat until satiety sometimes, especially if you fear harm from severe thinness, because restricting oneself to one-third is for those whom it does not weaken. However, for those whom it does weaken, they should eat what provides them with energy and a balanced physique.

The jurists mentioned that eating has stages: 1. Obligatory (Fard): What averts destruction. 2. Rewarded (Ma'joor 'alayh): What exceeds that, enabling one to perform acts of obedience. 3. Permissible (Mubah): What exceeds that, up to satiety, to increase bodily strength. 4. Forbidden (Haram): Eating beyond satiety, unless it is intended for strengthening oneself for the fast of the morrow or so that the guest does not feel ashamed.

Eating beyond satiety is disliked if it leads to indigestion.