Would you offer a gin and tonic to a recovering alcoholic? What about some heroin to a recovering heroine addict? I don't know too many people who would. It's frowned upon. It's not politically correct, aggressive, rude and you are viewed as an enabler.
Why is it OK to offer, heckle and shame people that refuse food for whatever reason they might have?
If someone is trying to lose weight - LET THEM.
If someone refused a plate of bread and they are allergic to gluten - LET IT GO.
If someone doesn't feel like dessert - DON'T PUSH IT.
If you want to eat a doughnut filled with empty calories, don't do whatever you can to entice me so I eat one too and make you feel better. Despite the fact that the Gluten in the sugar bomb will give me a 4 day asthma attack and bloat me two sizes, sugar is still hard to say no to. So if I say "No Thanks!" three times I probably mean it.