In the book, they talk about the conscious thought that's required up front to eat intuitively. At first, it feels like there's a whole lot to think about when identifying hunger and fullness. They compare it to a new driver. When you first start driving, you have to think through the steps - put your foot on the brake, turn the car on, put it in reverse, check the mirrors or camera, back out of the driveway, don't hit the trash can. Thinking, thinking, thinking, but with practice you can do all of that smoothly while your mind is elsewhere.
And yes, that thing about sugar. When I was restricting it, I couldn't stop eating it. It felt so dangerous and irresistible. I think dieting in general gave me that feeling. Restrict your food and you experience: obsessive food thoughts, cravings for high-calorie, high-reward foods, "now's my chance" eating when food is available, difficulty stopping eating, and eventual weight gain. Dieting was was making me a food-obsessed overeater. Oops! Not the result I was going for.