Less than you'd think. On the plan I described you pretty much just eat when hungry, until you're full.
You do need to say "potato chips and candy bars are not things I eat", or have some other mechanism for limiting those without willpower (dessert used to fill this function).
But I hardly need willpower to eat this way, because the body's system handle telling me when to eat.
Well, anecdotally, as someone who lost 100 pounds and kept it off for several years, the mechanisms in place don't work for everyone. I can easily eat a whole "American-sized" restaurant meal without thinking, whereas lean people tend to feel completely stuffed after eating, say, half a sandwich and a few fries.
Also, I get hunger sensations pretty much all the time, no matter how much I eat or how satiating the food is. The worst is that I actually get hunger sensations for quite a while after I eat. I suspect this can be the case for many obese people. For me, I need to use my eyes to regulate my eating rather than my hormones.
The amount of willpower necessary can vary considerably from one person to another, and for people like me just 'eating when hungry until I'm full' is not an option.
But you're definitely right about focusing on better food quality rather than simply eating less. It's far too easy to go overboard eating plates of spaghetti and meatballs than it is grilled-chicken atop salad. After I lost weight and cleaned up my diet, I now perfer the latter to the former. When my diet is consistently clean, it's easier to maintain the cleanliness. There's a lot of inertia when it comes to eating and controlling the velocity is far more valuable than just changing the speed.
Very interesting, thank you for your comment. I'd like to know more about hunger disregulation: does it cause initial weight gain, or is it the result of carrying extra adipose tissue, and does it reverse under any conditions.
Also I agree with your point about consistent cleanliness. I find it very easy to avoid eating something if it's a habit. I find it very hard to "limit" a food except by hunger. And hunger doesn't work well with junk, even when hunger is functioning normally.
You do need to say "potato chips and candy bars are not things I eat", or have some other mechanism for limiting those without willpower (dessert used to fill this function).
But I hardly need willpower to eat this way, because the body's system handle telling me when to eat.