@trunumber Not my experience at all. I LOVE all things unhealthy and can easily over eat. Take-always, eating out, snacking on popcorn and chocolate in the evening. On a two week holiday I can put on a lot of weight if I eat what I want.
I've pretty much always been 'slim' but have had short periods of being slightly overweight. When overweight I need 'a diet' to get back to a healthy weight. To maintain my healthy weight I:
Don't even go down the snack/crisp/ready-meal/processed meat aisle on my weekly shop
Limit takeaways and eating out (but order what I want when I do)
Get out for more exercise
Try to get as much veg as I can into meals (hate veg!)
Don't snack - don't have things in the house to snack on
It is definitely a constant low-level effort rather than just not being bothered with food unless hungry. I could honestly happily eat crap all day long and be huge.
Like someone else said- knowing that when I put on a bit of weight, I will do something about it within a short time frame.
My small close group of friends range from slim to morbidly obese. Having spent lots of time with them over the last 20 years- including holidays- I'd say the differences are that the slim friends will move a lot more, always be up and out doing something whereas overweight friends will happily sit all day (Although this could be an effect rather than a cause); overweight friends have a very different idea of portion size and diet- will have 3 courses when out for a meal, or go back for more if a buffet, will constantly have snacks on the go, when doing a shop to bring for a group holiday it will be full of sausage rolls, pork pies, crisps, cans of drink, crisps, etc- nothing healthy in sight because 'we're on holiday', whereas slimmer friends will bring a range of food including fruit and bags of salad along with a small amount of 'junk food'.
So definitely within my group of friends and family I'd say it is about food choices and portions. The slimmer people are always making a conscious effort to eat reasonably healthily, stop when full and not eat unhealthy snacks. Although this is never an in-your-face 'I'm on a diet'. You have to look closely and know their routines to know that that is what they are doing.