I'm probably wrong as I am new to this low cal low carb diet thing.
As I understand it, you will loose weight on a low cal diet eating carbs (but slower), but reducing the carbs means you are forcing the body to turn fat into energy instead of using the carbs you are eating.
If you eat more carbs than the body requires for immediate energy, the excess will get stored around the body as fat.
If you can reduce carbs sufficiently to get your body into ketosis you will loose more weight than just using a low cal diet.
I am trying to go for low carb after a week on LT and so far I have managed to keep my body in ketosis, so hopefully I should see a few pounds go this week.
Hope this helps.