I suppose this is how someone who has never had to diet eats?
I've never been on a typical diet, but have excluded things in the past due to IBS and for health reasons.
I came to the conclusion that we are all different, as my experiences never seem to match those of most mumsnetters!
I gained a stone from simply drinking wine, as the weight fell back off again back to my default after quitting it, yet my food intake didn't alter.
A further weight gain also occurred during the three years I had gone very low carb. I didn't eat large portions or a silly amount of fat either. When I had established that my IBS hadn't got any better, I returned to eating decent bread and pasta and lost 9lbs. It's a fucking mystery to me, all of it!
I think the only sure fire way to avoid having to diet on and off throughout our lives is to not become too overweight in the first place. I am referring to the 'set point' thing, which I am sure most of you have come across. But I am no expert - can only say what I have seen in myself. People who don't diet tend to remain within a stone or so of their default long term. So enjoying treats without designating foods as 'good' or 'bad' seems to be a positive mindset. All things enjoyed in moderation, that old cliche, I suppose.
The knack would be long term balance, without the associated guilt or self loathing that a diet cycle can create. I also believe exercise is underrated these days. With so much conflicting information online it is difficult to parse anything anymore. I have always lost tone and gained fat when sedentary. So in answer to the question, I have always been in healthy weight range and am almost 50 now. I think the only thing I have noticed between myself and people who struggle is the perception of certain foods as bad. Life is too short to worry about carbs, the odd fizzy drink or cheeseburger. An excess of processed foods might be an issue, but most people who don't diet still enjoy them sometimes. Perhaps the deprivation encourages to binge cycle, which becomes difficult to step out of.
Food as a solitary focus seems to add fuel to the fire also.
Imagine a scenario that is bigger than the urge to loose weight (apocalypse, loss, etc). A person would likely forget to isolate food as a life issue, which in many cases could facilitate healthy weight loss or gain. I think what I am saying in my own garbled way is I believe there is a correlation between not being able to eat moderately and fixation. The less one fixates on food, the more likely a stable weight/relationship with it will occur.
Of course, some people restrict, I am not including them here as this is still fixation, even if the person is slim.