All diets do ensure you eat no more than you need. Some of us can't just eat less, and need to switch to the two macro nutrients that we have limits on. You can overeat protein, but it's hard and doesn't taste good after you've had enough, and it will be balanced by your eating less the next day. You simply can't eat more fat than you need, it will make you sick if you overeat by a lot, but overeat fat at all and you will excrete the excess
There is no limit but the size of your stomach and the hours in the day for carbohydrates
So it's easy to do no more calories than you need on low carb