I am no expert and this is just a comment. But I think that portion size has a lot to do with weight gain plus not listening to your body. Are you really hungry, for example? Or has it become habit to have three large meals a day at set times, especially when one is, like me, retired? I have always eaten little to no breakfast, even when younger, working and with young children and was busy. I still rarely have more than a small banana. Why? I am simply never hungry in the morning so I can’t see the point of forcing something down, even though we are lectured about it being the most important meal of the day. Similarly with lunch. Never that hungry, might have a yoghurt or piece of toast. In the evening I eat a small meal. My hungry time is later when I might eat a bar of chocolate, a packet of crisps, a sandwich or cheese and crackers or my favourite, yoghurt and muesli. I know I possibly have a smaller appetite compared to others but I rarely feel hungry with what I eat. When I see other members of my family, or when I eat out, I wonder at the huge platefuls of food they consume. With my own family, I think it’s habit. My parents were very food conscious and ate large potions. Both were overweight. I struggled with keeping up but was somewhat ridiculed if I didn’t. My sibling and her family kept up the tradition and are overweight now too. When I stay I’m astonished at how much and how often they eat! At 65 I am slimmer than I was at 18 with no effort other than listening to my body and only eating what I feel I need when I need it. And I deny myself NO treats whatsoever, I must add!