First of all, have a think about why you want a low carb beer. If you're on a diet then you want to lower your intake, increase your exercise or skip beer altogether. Full bodied, full flavoured and low carb beer is simply a myth. Most beer is already low in carbs because that's what the yeast eat up. However, the alcohol produced still contains calories so the difference in carbs is insignificant.
As Pollux suggested, you could also look at a lower alcohol beer (and hence lower calories) which can still have plenty of body and flavour. It's a bit harder with an extract beer as the malt has already been converted, you may need to add maltodextrin to give it some body. The other better alternative would be to steep some speciality grains (eg crystal malts or carapils), which will add body and flavour without too many extra fermentables.
The low carb fad is just a marketing ploy, unfortunately they get away with it. Do a search on the forums here for more info, it'll be well worth your while.