Jeni, heck no. There is no "one piece of cake" for me either. I just don't buy a full cake unless I accept that one cake is one serving.
I do that with other food too, though. French Bread. Cereal. Definitely sugar and flour, but other things too. And natural sugar is not safe really either. I've eaten a whole watermelon in a day or an entire bag of dried apricots, two pounds of bing cherries, or a whole 1500 calorie bag of trail mix. 3000 calories in ice cream. I'm not focused on just sugar and flour. Fruit IS sugar - so - I'm not eliminating fruit.
I've gotten better. I'm not willing to go the rest of my life without ice cream or cherries. So I just don't beat myself up over it any more. I know I'll binge on certain foods. I just don't start on those every day, because I know. I have a lot of foods I know will set me off.
I'm at 22 BMI and my bloodwork is spot on. Has been for years. I exercise. I still have these mini-binges, but I know how to recover now.
I've been working on this for twelve years. Complete restriction doesn't work for me long-term, I just limit my intake by logging calories over TIME. I know that if I eat an entire pumpkin pie I've gone way over my calories, fiber, salt and fat and I'll pay for it in discomfort. I just don't get down on myself about it...move on with lower fat and lower salt and more vegetables *not* in pie form in the next few days. What? Pumpkin pie is a vegetable. Isn't it?