Dry Enzyme’s will help make a low carb beer, as it is designed to turn carbohydrates into fermentable sugars & let your yeast ferment them then into alcohol. You will find you get a dry crisp beer when using the enzyme, and should get a lot less unfermented sugars in your finished product and in turn a lower carb beer than normal fermentation. However consult a doctor if you are a diabetic, to make an informed decision on you diet, and what is ok for your circumstances.
Diet and Diabetic Beer must conform to regulations and the main requirement is that they contain no unfermented sugars, no matter what the alcohol level is. In home brewing we assume that fermentation (both primary and secondary) ferments all the sugars available; however, the yeast cells usually leave a small percentage just as you don’t eat all the crumbs on your plate, & some higher sugars are un-fermentable.
Special formulation and treatments are necessary to ensure that regulations are met, when breweries make diet beer. Home brewed beers will always contain some minute quantities of unfermented sugars: however, many diabetics will tell you that well matured home brews give them fewer problems than non diabetic commercial beers.