Aren't a lot of people already doing exactly this because they have a disease or disability that makes them unable to chew and swallow food? Roger Ebert hasn't

Aren't a lot of people already doing exactly this because they have a disease or disability that makes them unable to chew and swallow food? Roger Ebert hasn't been able to eat solid food in years and is still kicking, so what's in the stuff that's keeping him alive?