At what point does weight loss affect health?

Hello,
I know it is a difficult process to watch when a loved one is declining. As any dementia advances weight loss is expected. This is part of the end-stage process of the disease. His will eat when he wants to and there is not much to be done about it. 
I am so glad that he is getting hospice care. As long as the weight loss is not a concern to him, I would let it go.
I wish you the best.
Margaret

Dad has been in hospice since late May.

Same with my 95 year old mom, end stage Alzheimer's. She won't eat much and is loosing weight.
I suggested someone always supervisize her eating, offer food at non-meal times, bring high calorie foods (even if junk food) to pump up the calorie count. Try different textures of foods.

Mother has started waking up at 10 pm and wanting an Ensure. They give it to her.

Sometimes the body is just shutting down and they can't tolerate food. It's so hard to watch.

After Dad experienced quite a weight loss, hospice was suggested.

My mom is stage 7 Alzheimer's. She is 5'2" and now weights a whopping 75 lbs. She eats/drinks about about 700-900 calories a day. She is still pretty strong in spite if it all. She has always been a fighter. Beat cancer twice. I guess she will be here until she decides she is ready to leave this Earth.

His AL keeps track of all residents meals. He is eating pretty good but has been transitioning to finger foods. Staff is going to try add add more snacks into his daily schedule.

If he is not eating and/or eating much, weight loss could lead to malnutrition. At a certain, point, the body will start to use muscle and any stored fat to fuel itself.