well, firstly, we can't assume that every large person is a glutton. but many are walking in this. and also we can see a skin-and bones person, and we can't assume they are anorexic, the reality of what they some are doing is present on their faces, etc. but God made some people skinny, and that glorified Him in them.
it's really more of a question about the bottom line, which is: is God in charge, or me? am i honoring Him with my body, or am i thinking about what the world or my flesh says is ok? i think any body-obsession is sinful, because it is an obsession of self. this can be gluttony, anorexia, and a whole range of others. i worked with some women last year who had several eating disorders and saw the destruction in their lives having been wrought by the devil's twisted works of control gone horribly wrong. i've struggled with many different eating-related sins over my life, and really it came down to me trying to decide things that God's Word clearly spoke on. in a way, i think that anorexia is a form of gluttony, because it is an indulgence of self. there is also emotional starvation and emotional gluttony, these are not good either. (unwillingness to be vulnerable among the saints, inappropriate close relationships, etc.). only God should control us. in Galatians, when He shows us that self-control is a fruit of the Spirit, i believe that is a Biblical self-control, not a self-obsession. self-control in the Godly sense means death to self and a reality of living that knows and shows God is in control. self-control in the unGodly sense means that i, in my own strength, need to control things outside of God's control. i know what is beautiful, i don't trust God to make a man find me beautiful, i think God didn't make me right, etc. or i am upset so i'll turn to food instead of praying and crying out to the Lord. i love food, so i'll eat indulgently...see what i mean? it means me taking the control and telling God how He should have run the universe instead of obeying with self-control,still under the leadership of the Holy Spirit. so whether that is overeating or undereating, we are rejecting God's perfect plan for our bodies being a living sacrifice and that's really where the issue lies. will we trust Him to teach us how to eat, or will we lean on our own understanding?
that said, i do have compassion for these groups, the same as i have compassion for anyone, and perhaps more so because the churches are not speaking on this, so you have a whole lot of confused people. (granted, everyone is responsible to be reading the Word prayerfully, and God is faithful to convict when He is sought. but still). i have a fully experiential knowledge of these struggles, so i know what it is like. but i do think that churches should address these issues for what they really are, which boils down to a refusal to trust God in all things.
granted, we all have things the Lord is bringing us through. oh, may we throw down our reigns and beg at His feet for mercy!! none of us is perfect. :)
please know this was written with love and compassion. i just think it is really under-addressed.
love you all.