My dad is 89 years old, has lung disease and is losing weight quickly. He says he’s always full. Any suggestions?

You may want him evaluated by his doctor. You can't make him eat. His brain no longer tells him when he is hungry or thirsty. You can try some Boost or ensure. Maybe some "good for him" snacks.

His body will eventually start to shut down. Trying to make him drink or eat will do more harm than good. You may want to consider Hospice. Its all about comfort.