My mom has dementia and is down to 70 lbs. How long can a body sustain itself at such a low body weight?

I struggle with my moms weight as well. Honestly, I did a lot of trial and error. With her having dementia she would think that she ate when she didn't. So, I make sure she takes a multvitamin/day, I feed her 3 meals a day her portion size which is small but she manages to clean her plate after an hour of eating I make a big thing about her being such a "good girl" but I make sure is eats veggies, fruit, I give her milk and juice along with water. mom is able to feed herself so I have made a rital to eat with her(I eat super slow like her so she don't feel rushed) and she seems to eat better, I thought that giving her bigger portions would help her gain weight however, it overwhelmed her. she has been holding steady at 85-90 lbs for 6 months. I am more focused on her maintain that weight than gaining like the doctors wants. I keep her on a strict feeding time as well as small snacks in between like applesause, fruit or a cookie. Good luck!

Dementia patients are amazing people. My my has had Alz. for years and I go to feed her twice a day at NH. I give her her meals purreed, liquids thickened, cranberry juice, buttermilk, and mighty shake/ensure and lots of water at those meals. She gopt down to 80lbs. and had to go to hosp. for fluids at one time. If they are in a nursing home this can happen quickly they are the "forgotton" ones.