I was slim all my life until I had my first child. Put on 6 stone in that pregnancy. Four stone fell off at once, and the last stone (I was a stone more, but that was fine as I was very thin orginally) took weaning, plus stopping finishing his meals off - he has food issues so there was a lot of waste.
I was a lot more careful with the second pregnancy and ate a lot more healthily. I still put on six stone.
It's a lot less to do with will power and a lot more to do with metabolism than I ever realised. I was starving in pregnancy and needed to eat a lot more, a lot more often. It was really humbling to understand that I was slim less because I was sensible about eating, and more because I just didn't get very hungry, usually.
Apparently we also have bacteria in our gut that they now believe drives food cravings, with those that thrive on unhealthy foods then overgrowing and making us crave more.
If you can afford it I think things like Hello Fresh are great as a short term step. They provide all pre-measured ingredients for a healthy diet so that you cook from scratch and eat well, but can't over-eat. We did that for a while because I realised my son's very restricted diet meant our daughter was developing a limited palate from underexposure, and yet I found balancing two sets of healthy meals exhausting to the point I wasn't doing it. That helped and we now use the recipes without paying for the weekly boxes.
The other big thing is that starch makes you fat, as does sugar. They are stored differently when you eat them to excess. I snack now on apples and cubes of cheddar, instead of biscuits, for example, and it seems to fill me up without making me crave more.
I also think we should have a rethink on what beauty is. Being overweight isn't that much of a health risk. Obesity yes; overweight no. My main reason now for wanting to watch my weight as I age is arthritis in my feet - it hurts to be fat. But I do honestly believe that people's metabolism is everything - I had birth injuries after my kids that in the second case led to abscesses, and I couldn't do much for a year while the NHS fannied around sorting them out. I was around the 13 stone mark. They fixed it, and now I am something between 9 and 10, which is right for a tall woman. I've not taken up more exercise - I just move faster, and more, and rest less... and crave less sugar, which I did when teetering close to sepsis all the time.
This is long and rambling: what I am trying to say is that it's less choice, in my experience, than messages sent from your body. Trying to alter your diet so you crave less carbs and sugar, in case the gut biome theory (that overgrown 'bad' bacteria want those foods, so you crave them, feed that bacteria, and then crave more) is correct seemed to work with me, and so did just being able to go out more. But mainly I just don't feel starving hungry, and when I did, weight was a battle. I think I spent years feeling virtuous about my weight, and like I controlled it, when I found that easy. The years I didn't find it easy I was fat. It was less about will power than I would ever have believed. So I take my hat off to women who feel that deep hunger, and still manage to maintain a healthy weight. It was beyond me at those times.
My son is constantly starving and about to be seen for endochrine testing as a result. We're hoping it's just a sensory need, and not some sort of syndrome, but again, the fact some medical conditions leave patients starving hungry when their calorie needs are more than met does indicate there's a lot more going on metabolically than we understand as yet. Hopefully medical science will move on and help in the future - meanwhile, willpower seems all there is. And it's tough.