One of the most powerful hormones signals the body to be hungry and eat — INSULIN. So they used to give anorexics shots of insulin — hunger too strong to resist.
Once a person has gone without eating for about 3 days, the appetite is suppressed - read this when reading about Gandhi hunger strikes. Giving a shot of insulin would interfere with the no appetite issue.
And I agree that mental health treatment is needed. However, it is equally important at this point to get some nutrition into this person. Even a pic line could help.