My mum is 90 with Alzheimer's. She has the appetite of a mouse but a very sweet tooth! - getting her to eat anything decent has been increasingly difficult over the past couple of years. She's naturally small & slim, but her weight is now down to 6 stone (stable for past 3 years) & she's very bony. She can't cook for herself, struggles with the toaster & microwave, & now can't even successfully make a cup of tea. The carers make her hot drinks & toast & jam or honey, or cereal.
She lives on cakes & biscuits, sweets, mini-trifles, choc-chip brioche buns, jam sponge puddings & custard - but if I'm lucky I occasionally tempt her with a tiny toasted cheese sandwich, or 2 fish fingers or 2 chiploatas in a sandwich (just one slice of bread) & even then she struggles to eat it all. I used to cook 'proper' meals & take them round every evening but she's gone off nearly everything she used to like, now only really wants sweet things. She does have 2 Aymes Complete Nutritional drinks every day, prescribed by her GP. So even on days she doesn't want to eat anything at least she has the drinks - good job she loves them!
She was seeing a dietician at hospital - now discharged - they are happy for her to eat as much of what she fancies as she can, but advised adding extra calories & fat wherever possible - switch to whole milk, mix in powdered skimmed milk to anything like likes soups, sauces, custard, milky drinks etc. & full-fat everything - biscuits with creamy filling, cream in coffee etc. But at 90 years old at least she's eating something - 'grazing' is a more appropriate word for it.