@Planet42
My sister is slim whereas I could do with losing a couple of stone.She eats whatever she wants and enjoys her food as much as I do. She loves to snack.The difference between her and myself is she always feels full much before I do and just stops. Her portion sizes are smaller because she genuinely has had enough. I can carry on eating loads before I get really full. It’s not fair that I didn’t get that genetically as well
See I'm just not sure that that is a genuine argument (although I know I could be completely wrong if a load of scientists want to give me some reliable research).
If I start eating a lot over a few weeks: two courses instead of 1, ordering nan and popadoms and chips with an Indian, slipping in more puddings after meals, upping portion size generally - especially of carbs, then I start feeling like I'm not full with just a normal sized meal. If I do a short term diet like the 5:2, then it doesn't take too long for me to feel satisfied with much smaller portions and to struggle with a full meal out at a pub and not be able to manage a desert - whereas if I've had a month of over eating, I'd manage it no problem.
As you say - you can eat more until you're 'really full'. I think a lot of people eat until they get to that feeling of 'couldn't eat another bite', whereas others just eat until they are full. I know that I do both. I dont think its genetics, i think its habbit.
I do think that it's about what portion size you are used to to feel full and think people (myself included) can be totally deluded about what a normal portion size is. Stayed with my SIL and I cooked a curry. She had those boil in the bag rice packets and I was shocked at how small it looked on the plate when I cooked one bag each.