I personally think condition would be a better word, it is caused by multiple factors and should be treated as more a mental issue as well and yes I'm talking from personal experience.
I am male and 11 years ago was touching 30 stone having struggled with weight all my life, I had no off switch when it came to food and could just eat and eat, I couldn't buy clothes in shops as nothing would fit and my back was in pain walking. My ex wife had an affair because I was so big and had no interest in anything and I don't blame her in that aspect, she felt unloved and felt lacking as even sex was impossible because of my size so I accept my part in why she did it.
Despite all that when I looked in the mirror I saw a thin person. That's why I say it's a condition.
I can't honestly say there was a light bulb moment that made me realise I had to do something
Fast forward now I have lost 12 stone through diet and exercise, I feel so much better and I have a life again, only last week I was Majorca with my lovely fiancee and went swimming in the sea and stood on the beach with no t-shirt on, something that I couldn't have dreamt of 11 years ago.
So OP my point is yes disease, illness, condition whatever you want to call it it is that. It's also complex and not easy, if anyone here is struggling please feel free to message me for support as I have been there..
Sorry for the long post