Alzheimer's is normally the opposite, people forget to eat. That's why you give them food on dark crockery so there is more contrast to notice the food. In the uk there's a thing called "deprivation of liberty" legislation with people with diminished capacity. You're not allowed to say to an adult that you care for that they can't do something in what amounts to their home, so you get a deprivation of liberty order. Example: we have an overweight man in one of the homes the charity I work for runs. He has downs so has a tendency to gain weight, and is therefore on a calorie controlled diet. There is an order which allows the carers to tell him he can't have high calorie foods, but even so the emphasis is on persuading him rather than laying the law down, so you would say "chocolate mousse is a bit high in calories John (not his real name but whatever), why don't you have a yoghurt instead?" and 9 times out of 10 he goes away happy. Decent carers should not let their patients be overweight!