Eating to one's fill not sin
7-9-2017 | IslamWeb
Question:
Assalaamu alaykum. I take medication to protect my bones due to a condition I have. I am unsure about eating extra food, in light of Islam. I was advised to do things like eat an extra slice of toast in the morning and so on. However, most of the time, I tend to hold back from eating too much of one thing. I would like to know; if I do eat extra portions of food, would this be seen as permissible in Islam? We are supposed to eat and sleep less. However, I sometimes sleep too much or not at all when I should, which is linked to habits or problems like depression. As for food, I do eat extra sometimes. Does this harm my soul and faith? I do not feel right when I eat too much, but if it helps my physical health as long as I exercise, could it be permissible in islam? I worry that it causes problems with my heart and soul, affecting my faith further, as I have trouble with it sometimes. Last year, I struggled when fasting whilst I was working and traveling. I felt weakness and used to feel sick often. I also managed to skip the pre-dawn meal in the last weeks and was affected with something regarding my relatives. Skipping the pre-dawn meal meant not eating food and not taking my medication for my bones. I have been anxious about fasting ever since whereas I used to look forward to it very much, and I did not use to work then. I do not want to miss any fasts, and I am also unsure about whether I could be exempt from fasting in such cases. I look forward to your advice. May Allaah reward you.
Answer:
All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad 
is His slave and Messenger.
There is nothing wrong for you to eat what you need to eat, and you are not sinful for eating what suffices you. You are not sinful even if you eat until you are full. What is forbidden is that a person eats beyond his needs and more than his fill, which may harm him.
Iyaadh said: [The following words from a hadeeth]:
“'They ate until they were full' is evidence of the permissibility of eating until one is full. What was reported from the Prophet and the Salaf (righteous predecessors) about the dislike of eating until one is full applies to doing this all the time, as this hardens the heart, makes one forget about the needy and their suffering, and makes him held accountable for more things. What is permitted is to eat one’s fill as long as he does not exceed the limits and it does not prevent him from fulfilling his obligations and does not constrict his breathing and cause indigestion. Whatever exceeds this extent is not permissible. The Prophet said, '...but if he must (fill his stomach), then one third for food, one third for frink, and one third for his breath.'”
In light of the above, it becomes clear that there is nothing wrong for you to eat your fill, and you can eat what you need. Rather, you should not refrain from eating what you need to eat. So if you need to eat something for an act of worship that you do and eating this food will give you the strength to do it, or you need to take a medicine and the like, then abandoning what you need to eat is dispraised.
As regards missing the pre-dawn meal, then this is contrary to the Sunnah, as the Prophet commanded us to eat the pre-dawn meal and legislated it for his nation. The Prophet clarified that there is blessing in it and that it distinguished between our fasting and the fasting of the People of the Book. Hence, you should not abandon the pre-dawn meal in the future, and seek the Help of Allah in fasting, and He will help you.
If you have an excuse for not fasting, such as an illness or the like, then there is no harm on you to break the fast and then make up for it later.
Allah knows best.