How do I know when my wife (Doris) has enough to eat & or drink?

MrJoeMerc: Perhaps Doris requires less food and drink than a well individual since unfortunately she suffers from dementia.

With dementia and age, Doris's appetite will likely diminish. If she's pretty sedentary, not getting much exercise running around, she requires very few calories to thrive. So even if she eats a few bites of protein for her meals, she's probably doing okay, unless she's losing a lot of weight. You may want to serve her 6 small, snack like meals a day rather than 3 larger meals. Dementia folks often prefer that. Liquids can come in the form of water, juice, coffee, tea, or fruits like watermelon and grapes. Smoothies in the blender with berries, ice cream and milk is also a good way to get calories and fluids into her.

I would discuss this with the doctor if there are concerns that you have.
Most medical plans will allow you to speak with a nutritionist to discuss individual issues if there is a problem.

Can you tell us a little bit about what worry has led you to ask us this question?

You will know she has enough to eat if her weight is stable. Is she eating a balanced diet? Does she take any nutritional supplements? If her weight is stable, I would ask her Primary Care provider if they want her to take any supplements.

As for fluids, she should urinate every 3-4 hours if she is well hydrated.