Biting someone's head off - um, were you planning on eating it??
Once you are banded and at your 'sweet spot', the amount of food you will need to be 'full' will be less. Of course you are hungry now as you haven't yet been banded so your stomach is used to more, more and more food.
The nutritionist is trying to get you to eat this way now so that it will be second nature by the time you are banded thereby minimizing the overall adjustments and stress.
Reading the many posts on this site and others, most long-time banders consistently say they eat what they want, just less of it. Some seem to have one or 2 foods that are problematic, but not entire groups of foods.
Good luck on your journey, whatever your decision.