Allah commands: "Eat and drink, but do not be excessive; indeed He does not love the excessive" (Qurʾān 7:31). The Prophet ﷺ said: "No human being fills a vessel worse than his stomach. It is enough for the son of Ādam to take a few morsels to keep his back straight; but if he must, then a third for his food, a third for his drink, and a third for his breath" (al-Tirmidhī 2380, graded ḥasan ṣaḥīḥ). Overeating is therefore blameworthy isrāf rather than a sin of the same class as eating ḥarām — it is disliked, harms the body which is an amānah from Allah, and dulls worship. Moderation in food is the prophetic norm, and a Muslim who is overweight for medical or hereditary reasons is not sinful; the accountability is on deliberate excess.
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.