My father in law is about 81 years old and he has difficulty in swallowing. His food consumption is very low and often accompanied by nausea. He feels that food get stuck on his throat

I had the same problem, I'm 44, until I started on Nexium. Have him ask his doctor to test him for GERD.

That can be a symptom of Alzheimer's, among other things.

Is he showing signs of forgetfulness?