Dr Johnson's recommendation is to eat until satisfied but not stuffed. You don't have to eat up to a certain number of calories, but neither do you have to stick to a certain limit.
At the same time, UD's are not a licence to stuff yourself silly, nor to fill yourself with sugar, processed carbs and fat - you will do better overall if most of what you eat is healthy. But you shouldn't need to count calories, nor do you need to limit yourself to low calorie/low carb/low fat food for JUDDD to work.
Eat real food, enough to satisfy, but don't pig out. End of.
Barbara