Islam ordered us to maintain our bodies and to take care of them. We are responsible for that as we are merely trustees and Allah will ask us about our health and youth. Thus, both the Qur’an and sunna urge us to follow a moderate way in everything especially in issues relate to eating and drinking.
It is not and it cannot be a sin at all because you are fat. Just you need to follow the moderate way in eating and drinking as the Holy Qur’an ordered us. For Allah says: [O Children of Adam! wear your beautiful apparel at every time and place of prayer: eat and drink: But waste not by excess, for Allah loveth not the wasters.] ( AlA’raf 7:31)

The Prophet (peace and blessings be upon him is reported to have said:one third for his (her) food, one third for his (her) drinking, and one third for his (her) breath.”

For the time being, an oversized person needs to see a specialist as this could cause loads of health problems that could be avoided if there was an honest and efficient consultant.

May Allah guide us to the right path in this life and the hereafter.Ameen.