I've felt slightly uncomfortable if I've gone to stay places and they are absolutely constantly trying to feed me. Not just at conventional mealtimes but inbetween as well. (Have these chocolates/crisps. Oh go on. I bought them specially.)
If I am visiting friends it's to see them. To talk and catch up on their news. Maybe to go out and see places in the area as well. I enjoy food and talking over a meal is lovely. But for me maybe snacking and grazing is associated with boredom. It's what you do more when life is frankly a bit dull or you're feeling slightly low. So constantly wanting/expecting to be fed at somebody's house - to me- implies 'It's a bit boring here. I want more stimulus. Your house, your books, your children, your games and suggested actitvities, your music, your conversation and DVD collection. They're not enough.'
Obviously children need feeding more regularly and if a visitor was diabetic, I'd be mindful of their needs. Both offering them something more regularly and indicating that they must help themselves.
It maybe a slightly old-fashioned feeling that the 'proper' way to behave is to offer three meals plus something akin to afternoon tea, and that most civilised adults - unless they have medical needs - will have the maturity and flexibility to make the best of what's on offer and even show gratitude. It is - or was - a fairly normal way of eating and living.
I suspect that I'd put up with friends who have rather different needs - and were insistent on making those needs known - for a short period. But would be quite glad when they left!