Along with the good advice you've been given about giving the shot after a meal, I think you may want to change how food is referred to for the moment. Kids pick up on our own "anxieties", even if we think we control them. So, I can imagine my own kid hearing me say to eat his carbs, well, he'll ask why and refuse, just because he can. I would avoid the term "carbs" for a while. I know, sounds silly, but it's causing a power struggle between you and him. You want him to have the carbs, well, he'll just avoid the carbs. Did I make sense? Anyway, and yes replace the candy with some yummy no-flavour glucose tabs. And definitely reward when it's needed. On the slow-eater front...sigh...I know the feeling.