I found in the early days, My Mother was advised to eat healthily, supposedly to slow down her dementia! She was, as we all are, also advised to drink more as her brain was dehydrated! She ignored all of this advice even though we stickered almost every surface with reminders and when she did eat she did so with gusto. Later changed - she literally lost all motivation and forgot to eat. Struggled with holding cutlery
My advice would be (if your loved one is losing weight)
Don’t worry about set mealtimes
Don’t remove food or take food away just because they say no initially.
Offer bright coloured food
Stop worrying about healthy food let them eat anything they fancy even if that’s Jaffa cakes or bacon for every meal. You can always give build up drinks or add vitamins in other ways.