I think it's incredibly reductive to look at 2/3 of the population and say 'they've all got psychological problems with food'.
It's the food industry and;
- I think UPF's drive cravings that whole/natural foods don't
- everyone is running on sugar and carbs which makes you want to eat more sugar and carbs
- the glucose rollar coaster many people are on
- the normalisation of ever increasing portion sizes
- the cheapness of UPF food
- the extra hours working and demands placed on most of us means we're rushing back from work to get something 'stuck on for dinner' that will be as quick and easy as possible - rather than one person being stay at home making food from scratch
- the lack of a 'village' - quite literally. Alot of people don't live walking distance to a butcher/green grocer - so we're all getting in our cars to hit Sainsbury's/Tesco
- people are just fucking tired these days - driving poor food choices even further
- a whole billion pound diet industry giving mixed messages about what we should be doing/eating. It's all conflicting info.
- the retail sector increasing the size of clothes so we still feel we're an acceptable size (e.g current size 12 - would probably have been a size 16 - 20-30yrs ago)
- the downward fall of fat shaming - which is good but now most people are overweight we don't feel the pressure to lose weight because we feel normal compared to most people we see around and it's unlikely your manager at work/your bestmate is ever going to say - bloody hell you packed on a few pounds recently haven't you?
- the fitness industry becoming so over the top it's off putting
But if i had to boil it down to a couple of things - the crap in our food is leading us to feel hungrier more often, this along with large portions and large sized clothing being normalised is what's causing obesity.
So why do I think slim people are slim? If we put to one side the people who work really hard to stay in shape - those who are extra careful about what they eat and always exercise, then I think the slim people who don't seem to gain weight but who are not people obsessed about 'being slim' - probably did luck out genetically and probably don't eat ready meals.
But I also want to flag the point that most people who think they are slim are probably not as slim as they think. They fit into size 10 M&S jeans and feel great about it. Failing to recognise that those size 10 jeans were likely a size 14-16 back in the 70s. If you roll back to that time, they themselves may have been considered 'a larger lady'.
It's a false sense of accomplishment to bask in slim smugness when the population around you is growing larger and larger.
We have family in the USA who think DH and I are 'slim' and by their measure we are. In the UK - we're firmly 'overweight'. I'm a size 16 UK sizing (now) in the USA that's a size 12. My DH wears XL tops in the USA he was a medium. If we moved to the USA we could feel smug about how 'slim we are' and what good control we have over our eating.
Essentially everyone's perception of slim is now skewed.
I wonder how many self proclaimed slim people on this thread might get a shock if they spent some time in Japan.....
The slim people in the UK are not exempt from the issue - they are getting larger along with everyone else they are just slim in comparison. If you have a BMI of 23 and you delight in your own slimness just remember you'd be considered average (not slim) in Japan and might be told to exercise a bit more or have someone wide eyed looking at the size of your portion when eating lunch.
So to boil it down to psychological problems /no will power/ they don't eat right is to spectacularly fail to understand your own place in this quite literally growing problem.....which starts with the food industry, and is aided by the deprioritisation of family meal time, long working hours, dual parental incomes required to live etc etc etc.
Willpower/diet motivation is a small part of a much more complex issue. If 2/3 of the population were unemployed no one would say 'they all don't have the motivation to find work'. You'd say the system is broken.
Our food industry is broken but only for the people. For those running it - it's hugely profitable and as a result we'll continue to get fatter (including the slim people).....until something snaps.