Is unhealthy eating or overeating (to the point of fullness) considered a sin?

Eating beyond satiety is makrooh tanzeehan (reprehensible in a minor degree) as long as it does not cause harm. However, if it leads to certain harm for the eater, then it is haram (forbidden). As for unhealthy eating, it is not forbidden in itself unless its harm is confirmed by the testimony of specialists.

Scholars have mentioned categories for eating: - Obligatory (Fard): What prevents destruction. - Rewarded (Ma'joor 'alayh): What is increased to support worship. - Permissible (Mubah): What is increased to satiety without harm. - Forbidden (Haram): Eating beyond satiety, except for a legitimate purpose such as fasting the next day or honoring a guest.

The Sunnah states that the stomach should be divided into three parts: one-third for food, one-third for drink, and one-third for air.