Frosty - I never have said unhealthy snacks are needed and I too suggested healthy alternative snacks/smaller meals in my first post. But I also think suggesting fruit/crudités is ridiculous in the other extreme as they don't provide enough calories.
"I think it’s important to have a balance and to provide healthy snacks and meals 80% of the time and allow some not so healthy choices the rest of the time." On this we agree and you've also said going to the too restrictive end of things isn't the answer either.
I'll be honest I'm overweight now but I was slim until mid 30's. Siblings are still both slim, parents are slim.
In my case it's partially due to:
medication (on 2 kinds which can reduce metabolic rate),
reduced mobility due to disability
mh issues mean I tend to feast or famine - anxiety makes me unable to eat - stomach "in knots" then when the anxiety goes I'm starving and crave stodge. So that will have messed with my metabolism too. I do tend to try and keep to a healthy diet but eg going through a period of high anxiety at the moment and if I manage a sandwich a day, maybe a yogurt too, I'm doing well.
Despite this I did actually lose 1.5 stone a few years ago and have kept it off.
Moderation is the key. Dd does far better than me. Low sugar high fibre cereal or wholemeal toast for breakfast, sandwich at work for lunch or maybe a baked potato or salad (there's a canteen), I'll cook her tea at home and that will be something healthy usually, stir fry with lots of veg served with plain rice or cous cous, pasta with sauce, casserole, stew, frittata, salads in the summer with boiled eggs or Ham for protein. But she does like crisps (as I said tends to crave them at time of month), the tiny bags of haribo, sweet breads (malt loaf, teacakes, cinnamon bread), and sometimes burger or kfc or similar (but hates chips so it's JUST a burger or chicken wings or whatever she has and a drink). So not perfect - but balanced.