It's my basic understanding that, all things being equal, which they never are, on low carb you will reduce the amount of carbohydrate you consume, you only need a certain amount of protein a day for body maintenance another controversial topic on exact amount for the "average person" of which I have met none.

So, without throwing weight loss into the matter (metabolizing your own fat) you will need to eat the 3rd macro to meet your daily, ever changing, sustenance - You will eat FAT.

Sorry for the convolutions but there you have it from my perspective today.